src/Tizen.NUI.Components/Controls/ScrollableBase.cs

   1 /* Copyright (c) 2021 Samsung Electronics Co., Ltd.
   2  *
   3  * Licensed under the Apache License, Version 2.0 (the "License");
   4  * you may not use this file except in compliance with the License.
   5  * You may obtain a copy of the License at
   6  *
   7  * http://www.apache.org/licenses/LICENSE-2.0
   8  *
   9  * Unless required by applicable law or agreed to in writing, software
  10  * distributed under the License is distributed on an "AS IS" BASIS,
  11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12  * See the License for the specific language governing permissions and
  13  * limitations under the License.
  14  *
  15  */
  16 using System;
  17 using Tizen.NUI.BaseComponents;
  18 using System.Collections.Generic;
  19 using System.ComponentModel;
  20 using System.Diagnostics;
  21 using System.Runtime.InteropServices;
  22 using Tizen.NUI.Accessibility;
  23
  24 namespace Tizen.NUI.Components
  25 {
  26     /// <summary>
  27     /// ScrollEventArgs is a class to record scroll event arguments which will sent to user.
  28     /// </summary>
  29     /// <since_tizen> 8 </since_tizen>
  30     public class ScrollEventArgs : EventArgs
  31     {
  32         private Position position;
  33         private Position scrollPosition;
  34
  35         /// <summary>
  36         /// Default constructor.
  37         /// </summary>
  38         /// <param name="position">Current container position</param>
  39         /// <since_tizen> 8 </since_tizen>
  40         public ScrollEventArgs(Position position)
  41         {
  42             this.position = position;
  43             this.scrollPosition = new Position(-position);
  44         }
  45
  46         /// <summary>
  47         /// Current position of ContentContainer.
  48         /// </summary>
  49         /// <since_tizen> 8 </since_tizen>
  50         public Position Position
  51         {
  52             get
  53             {
  54                 return position;
  55             }
  56         }
  57         /// <summary>
  58         /// Current scroll position of scrollableBase pan.
  59         /// This is the position in the opposite direction to the current position of ContentContainer.
  60         /// </summary>
  61         [EditorBrowsable(EditorBrowsableState.Never)]
  62         public Position ScrollPosition
  63         {
  64             get
  65             {
  66                 return scrollPosition;
  67             }
  68         }
  69     }
  70
  71     /// <summary>
  72     /// ScrollOutofBoundEventArgs is to record scroll out-of-bound event arguments which will be sent to user.
  73     /// </summary>
  74     [EditorBrowsable(EditorBrowsableState.Never)]
  75     public class ScrollOutOfBoundEventArgs : EventArgs
  76     {
  77         /// <summary>
  78         /// The direction to be touched.
  79         /// </summary>
  80         [EditorBrowsable(EditorBrowsableState.Never)]
  81         public enum Direction
  82         {
  83             /// <summary>
  84             /// Upwards.
  85             /// </summary>
  86             [EditorBrowsable(EditorBrowsableState.Never)]
  87             Up,
  88
  89             /// <summary>
  90             /// Downwards.
  91             /// </summary>
  92             [EditorBrowsable(EditorBrowsableState.Never)]
  93             Down,
  94
  95             /// <summary>
  96             /// Left bound.
  97             /// </summary>
  98             [EditorBrowsable(EditorBrowsableState.Never)]
  99             Left,
 100
 101             /// <summary>
 102             /// Right bound.
 103             /// </summary>
 104             [EditorBrowsable(EditorBrowsableState.Never)]
 105             Right,
 106         }
 107
 108         /// <summary>
 109         /// Constructor.
 110         /// </summary>
 111         /// <param name="direction">Current pan direction</param>
 112         /// <param name="displacement">Current total displacement</param>
 113         [EditorBrowsable(EditorBrowsableState.Never)]
 114         public ScrollOutOfBoundEventArgs(Direction direction, float displacement)
 115         {
 116             PanDirection = direction;
 117             Displacement = displacement;
 118         }
 119
 120         /// <summary>
 121         /// Current pan direction of ContentContainer.
 122         /// </summary>
 123         [EditorBrowsable(EditorBrowsableState.Never)]
 124         public Direction PanDirection
 125         {
 126             get;
 127         }
 128
 129         /// <summary>
 130         /// Current total displacement of ContentContainer.
 131         /// if its value is greater than 0, it is at the top/left;
 132         /// if less than 0, it is at the bottom/right.
 133         /// </summary>
 134         [EditorBrowsable(EditorBrowsableState.Never)]
 135         public float Displacement
 136         {
 137             get;
 138         }
 139     }
 140
 141     /// <summary>
 142     /// This class provides a View that can scroll a single View with a layout. This View can be a nest of Views.
 143     /// </summary>
 144     /// <since_tizen> 8 </since_tizen>
 145     public class ScrollableBase : Control
 146     {
 147         static bool LayoutDebugScrollableBase = false; // Debug flag
 148         private Direction mScrollingDirection = Direction.Vertical;
 149         private bool mScrollEnabled = true;
 150         private int mScrollDuration = 125;
 151         private int mPageWidth = 0;
 152         private float mPageFlickThreshold = 0.4f;
 153         private float mScrollingEventThreshold = 0.001f;
 154
 155         private class ScrollableBaseCustomLayout : AbsoluteLayout
 156         {
 157             protected override void OnMeasure(MeasureSpecification widthMeasureSpec, MeasureSpecification heightMeasureSpec)
 158             {
 159                 MeasuredSize.StateType childWidthState = MeasuredSize.StateType.MeasuredSizeOK;
 160                 MeasuredSize.StateType childHeightState = MeasuredSize.StateType.MeasuredSizeOK;
 161
 162                 Direction scrollingDirection = Direction.Vertical;
 163                 ScrollableBase scrollableBase = this.Owner as ScrollableBase;
 164                 if (scrollableBase != null)
 165                 {
 166                     scrollingDirection = scrollableBase.ScrollingDirection;
 167                 }
 168
 169                 float totalWidth = 0.0f;
 170                 float totalHeight = 0.0f;
 171
 172                 // measure child, should be a single scrolling child
 173                 foreach (LayoutItem childLayout in LayoutChildren)
 174                 {
 175                     if (childLayout != null && childLayout.Owner.Name == "ContentContainer")
 176                     {
 177                         // Get size of child
 178                         // Use an Unspecified MeasureSpecification mode so scrolling child is not restricted to it's parents size in Height (for vertical scrolling)
 179                         // or Width for horizontal scrolling
 180                         if (scrollingDirection == Direction.Vertical)
 181                         {
 182                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(heightMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 183                             MeasureChildWithMargins(childLayout, widthMeasureSpec, new LayoutLength(0), unrestrictedMeasureSpec, new LayoutLength(0)); // Height unrestricted by parent
 184                         }
 185                         else
 186                         {
 187                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(widthMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 188                             MeasureChildWithMargins(childLayout, unrestrictedMeasureSpec, new LayoutLength(0), heightMeasureSpec, new LayoutLength(0)); // Width unrestricted by parent
 189                         }
 190
 191                         totalWidth = (childLayout.MeasuredWidth.Size + (childLayout.Padding.Start + childLayout.Padding.End)).AsDecimal();
 192                         totalHeight = (childLayout.MeasuredHeight.Size + (childLayout.Padding.Top + childLayout.Padding.Bottom)).AsDecimal();
 193
 194                         if (childLayout.MeasuredWidth.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 195                         {
 196                             childWidthState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 197                         }
 198                         if (childLayout.MeasuredHeight.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 199                         {
 200                             childHeightState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 201                         }
 202                     }
 203                 }
 204
 205                 MeasuredSize widthSizeAndState = ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 206                 MeasuredSize heightSizeAndState = ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 207                 totalWidth = widthSizeAndState.Size.AsDecimal();
 208                 totalHeight = heightSizeAndState.Size.AsDecimal();
 209
 210                 // Ensure layout respects it's given minimum size
 211                 totalWidth = Math.Max(totalWidth, SuggestedMinimumWidth.AsDecimal());
 212                 totalHeight = Math.Max(totalHeight, SuggestedMinimumHeight.AsDecimal());
 213
 214                 widthSizeAndState.State = childWidthState;
 215                 heightSizeAndState.State = childHeightState;
 216
 217                 SetMeasuredDimensions(ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, childWidthState),
 218                     ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, childHeightState));
 219
 220                 // Size of ScrollableBase is changed. Change Page width too.
 221                 if (scrollableBase != null)
 222                 {
 223                     scrollableBase.mPageWidth = (int)MeasuredWidth.Size.AsRoundedValue();
 224                     scrollableBase.OnScrollingChildRelayout(null, null);
 225                 }
 226             }
 227         } //  ScrollableBaseCustomLayout
 228
 229         /// <summary>
 230         /// The direction axis to scroll.
 231         /// </summary>
 232         /// <since_tizen> 8 </since_tizen>
 233         public enum Direction
 234         {
 235             /// <summary>
 236             /// Horizontal axis.
 237             /// </summary>
 238             /// <since_tizen> 8 </since_tizen>
 239             Horizontal,
 240
 241             /// <summary>
 242             /// Vertical axis.
 243             /// </summary>
 244             /// <since_tizen> 8 </since_tizen>
 245             Vertical
 246         }
 247
 248         /// <summary>
 249         /// Scrolling direction mode.
 250         /// Default is Vertical scrolling.
 251         /// </summary>
 252         /// <since_tizen> 8 </since_tizen>
 253         public Direction ScrollingDirection
 254         {
 255             get
 256             {
 257                 return mScrollingDirection;
 258             }
 259             set
 260             {
 261                 if (value != mScrollingDirection)
 262                 {
 263                     //Reset scroll position and stop scroll animation
 264                     ScrollTo(0, false);
 265
 266                     mScrollingDirection = value;
 267                     mPanGestureDetector.ClearAngles();
 268                     mPanGestureDetector.AddDirection(value == Direction.Horizontal ?
 269                         PanGestureDetector.DirectionHorizontal : PanGestureDetector.DirectionVertical);
 270
 271                     ContentContainer.WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent;
 272                     ContentContainer.HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent;
 273                     SetScrollbar();
 274                 }
 275             }
 276         }
 277
 278         /// <summary>
 279         /// Enable or disable scrolling.
 280         /// </summary>
 281         /// <since_tizen> 8 </since_tizen>
 282         public bool ScrollEnabled
 283         {
 284             get
 285             {
 286                 return mScrollEnabled;
 287             }
 288             set
 289             {
 290                 if (value != mScrollEnabled)
 291                 {
 292                     mScrollEnabled = value;
 293                     if (mScrollEnabled)
 294                     {
 295                         mPanGestureDetector.Detected += OnPanGestureDetected;
 296                     }
 297                     else
 298                     {
 299                         mPanGestureDetector.Detected -= OnPanGestureDetected;
 300                     }
 301                 }
 302             }
 303         }
 304
 305         /// <summary>
 306         /// Gets scrollable status.
 307         /// </summary>
 308         [EditorBrowsable(EditorBrowsableState.Never)]
 309         protected override bool AccessibilityIsScrollable()
 310         {
 311             return true;
 312         }
 313
 314         /// <summary>
 315         /// Pages mode, enables moving to the next or return to current page depending on pan displacement.
 316         /// Default is false.
 317         /// </summary>
 318         /// <since_tizen> 8 </since_tizen>
 319         public bool SnapToPage { set; get; } = false;
 320
 321         /// <summary>
 322         /// Get current page.
 323         /// Working property with SnapToPage property.
 324         /// </summary>
 325         /// <since_tizen> 8 </since_tizen>
 326         public int CurrentPage { get; private set; } = 0;
 327
 328         /// <summary>
 329         /// Duration of scroll animation.
 330         /// Default value is 125ms.
 331         /// </summary>
 332         /// <since_tizen> 8 </since_tizen>
 333         public int ScrollDuration
 334         {
 335             set
 336             {
 337                 mScrollDuration = value >= 0 ? value : mScrollDuration;
 338             }
 339             get
 340             {
 341                 return mScrollDuration;
 342             }
 343         }
 344
 345         /// <summary>
 346         /// Scroll Available area.
 347         /// </summary>
 348         /// <since_tizen> 8 </since_tizen>
 349         public Vector2 ScrollAvailableArea { set; get; }
 350
 351         /// <summary>
 352         /// An event emitted when user starts dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 353         /// </summary>
 354         /// <since_tizen> 8 </since_tizen>
 355         public event EventHandler<ScrollEventArgs> ScrollDragStarted;
 356
 357         /// <summary>
 358         /// An event emitted when user stops dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 359         /// </summary>
 360         /// <since_tizen> 8 </since_tizen>
 361         public event EventHandler<ScrollEventArgs> ScrollDragEnded;
 362
 363         /// <summary>
 364         /// An event emitted when the scrolling slide animation starts, user can subscribe or unsubscribe to this event handler.<br />
 365         /// </summary>
 366         /// <since_tizen> 8 </since_tizen>
 367         public event EventHandler<ScrollEventArgs> ScrollAnimationStarted;
 368
 369         /// <summary>
 370         /// An event emitted when the scrolling slide animation ends, user can subscribe or unsubscribe to this event handler.<br />
 371         /// </summary>
 372         /// <since_tizen> 8 </since_tizen>
 373         public event EventHandler<ScrollEventArgs> ScrollAnimationEnded;
 374
 375         /// <summary>
 376         /// An event emitted when scrolling, user can subscribe or unsubscribe to this event handler.<br />
 377         /// </summary>
 378         /// <since_tizen> 8 </since_tizen>
 379         public event EventHandler<ScrollEventArgs> Scrolling;
 380
 381         /// <summary>
 382         /// An event emitted when scrolling out of bound, user can subscribe or unsubscribe to this event handler.<br />
 383         /// </summary>
 384         [EditorBrowsable(EditorBrowsableState.Never)]
 385         public event EventHandler<ScrollOutOfBoundEventArgs> ScrollOutOfBound;
 386
 387         /// <summary>
 388         /// Scrollbar for ScrollableBase.
 389         /// </summary>
 390         /// <since_tizen> 8 </since_tizen>
 391         public ScrollbarBase Scrollbar
 392         {
 393             get
 394             {
 395                 return scrollBar;
 396             }
 397             set
 398             {
 399                 if (scrollBar)
 400                 {
 401                     base.Remove(scrollBar);
 402                 }
 403                 scrollBar = value;
 404
 405                 if (scrollBar != null)
 406                 {
 407                     scrollBar.Name = "ScrollBar";
 408                     base.Add(scrollBar);
 409
 410                     if (hideScrollbar)
 411                     {
 412                         scrollBar.Hide();
 413                     }
 414                     else
 415                     {
 416                         scrollBar.Show();
 417                     }
 418
 419                     SetScrollbar();
 420                 }
 421             }
 422         }
 423
 424         /// <summary>
 425         /// Always hide Scrollbar.
 426         /// </summary>
 427         /// <since_tizen> 8 </since_tizen>
 428         public bool HideScrollbar
 429         {
 430             get
 431             {
 432                 return hideScrollbar;
 433             }
 434             set
 435             {
 436                 hideScrollbar = value;
 437
 438                 if (scrollBar)
 439                 {
 440                     if (value)
 441                     {
 442                         scrollBar.Hide();
 443                     }
 444                     else
 445                     {
 446                         scrollBar.Show();
 447                     }
 448                 }
 449             }
 450         }
 451
 452         /// <summary>
 453         /// Container which has content of ScrollableBase.
 454         /// </summary>
 455         /// <since_tizen> 8 </since_tizen>
 456         public View ContentContainer { get; private set; }
 457
 458         /// <summary>
 459         /// Set the layout on this View. Replaces any existing Layout.
 460         /// </summary>
 461         /// <since_tizen> 8 </since_tizen>
 462         public new LayoutItem Layout
 463         {
 464             get
 465             {
 466                 return ContentContainer.Layout;
 467             }
 468             set
 469             {
 470                 ContentContainer.Layout = value;
 471             }
 472         }
 473
 474         /// <summary>
 475         /// List of children of Container.
 476         /// </summary>
 477         /// <since_tizen> 8 </since_tizen>
 478         public new List<View> Children
 479         {
 480             get
 481             {
 482                 return ContentContainer.Children;
 483             }
 484         }
 485
 486         /// <summary>
 487         /// Deceleration rate of scrolling by finger.
 488         /// Rate should be bigger than 0 and smaller than 1.
 489         /// Default value is 0.998f;
 490         /// </summary>
 491         /// <since_tizen> 8 </since_tizen>
 492         public float DecelerationRate
 493         {
 494             get
 495             {
 496                 return decelerationRate;
 497             }
 498             set
 499             {
 500                 decelerationRate = (value < 1 && value > 0) ? value : decelerationRate;
 501                 logValueOfDeceleration = (float)Math.Log(value);
 502             }
 503         }
 504
 505         /// <summary>
 506         /// Threshold not to go infinite at the end of scrolling animation.
 507         /// </summary>
 508         [EditorBrowsable(EditorBrowsableState.Never)]
 509         public float DecelerationThreshold { get; set; } = 0.1f;
 510
 511         /// <summary>
 512         /// Scrolling event will be thrown when this amount of scroll position is changed.
 513         /// If this threshold becomes smaller, the tracking detail increases but the scrolling range that can be tracked becomes smaller.
 514         /// If large sized ContentContainer is required, please use larger threshold value.
 515         /// Default ScrollingEventThreshold value is 0.001f.
 516         /// </summary>
 517         [EditorBrowsable(EditorBrowsableState.Never)]
 518         public float ScrollingEventThreshold
 519         {
 520             get
 521             {
 522                 return mScrollingEventThreshold;
 523             }
 524             set
 525             {
 526                 if (mScrollingEventThreshold != value && value > 0)
 527                 {
 528                     ContentContainer.RemovePropertyNotification(propertyNotification);
 529                     propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(value));
 530                     propertyNotification.Notified += OnPropertyChanged;
 531                     mScrollingEventThreshold = value;
 532                 }
 533             }
 534         }
 535
 536         /// <summary>
 537         /// Page will be changed when velocity of panning is over threshold.
 538         /// The unit of threshold is pixel per millisecond.
 539         /// </summary>
 540         /// <since_tizen> 8 </since_tizen>
 541         public float PageFlickThreshold
 542         {
 543             get
 544             {
 545                 return mPageFlickThreshold;
 546             }
 547             set
 548             {
 549                 mPageFlickThreshold = value >= 0f ? value : mPageFlickThreshold;
 550             }
 551         }
 552
 553         /// <summary>
 554         /// Padding for the ScrollableBase
 555         /// </summary>
 556         [EditorBrowsable(EditorBrowsableState.Never)]
 557         public new Extents Padding
 558         {
 559             get
 560             {
 561                 return ContentContainer.Padding;
 562             }
 563             set
 564             {
 565                 ContentContainer.Padding = value;
 566             }
 567         }
 568
 569         /// <summary>
 570         /// Alphafunction for scroll animation.
 571         /// </summary>
 572         [EditorBrowsable(EditorBrowsableState.Never)]
 573         public AlphaFunction ScrollAlphaFunction { get; set; } = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
 574
 575         private bool hideScrollbar = true;
 576         private float maxScrollDistance;
 577         private float childTargetPosition = 0.0f;
 578         private PanGestureDetector mPanGestureDetector;
 579         private ScrollbarBase scrollBar;
 580         private bool scrolling = false;
 581         private float ratioOfScreenWidthToCompleteScroll = 0.5f;
 582         private float totalDisplacementForPan = 0.0f;
 583         private Size previousContainerSize = new Size();
 584         private Size previousSize = new Size();
 585         private PropertyNotification propertyNotification;
 586         private float noticeAnimationEndBeforePosition = 0.0f;
 587         private bool readyToNotice = false;
 588
 589         /// <summary>
 590         /// Notice before animation is finished.
 591         /// </summary>
 592         [EditorBrowsable(EditorBrowsableState.Never)]
 593         // Let's consider more whether this needs to be set as protected.
 594         public float NoticeAnimationEndBeforePosition
 595         {
 596             get => noticeAnimationEndBeforePosition;
 597             set => noticeAnimationEndBeforePosition = value;
 598         }
 599
 600         // Let's consider more whether this needs to be set as protected.
 601         private float finalTargetPosition;
 602
 603         private Animation scrollAnimation;
 604         // Declare user alpha function delegate
 605         [UnmanagedFunctionPointer(CallingConvention.StdCall)]
 606         private delegate float UserAlphaFunctionDelegate(float progress);
 607         private UserAlphaFunctionDelegate customScrollAlphaFunction;
 608         private float velocityOfLastPan = 0.0f;
 609         private float panAnimationDuration = 0.0f;
 610         private float panAnimationDelta = 0.0f;
 611         private float logValueOfDeceleration = 0.0f;
 612         private float decelerationRate = 0.0f;
 613
 614         private View topOverShootingShadowView;
 615         private View bottomOverShootingShadowView;
 616         private View leftOverShootingShadowView;
 617         private View rightOverShootingShadowView;
 618         private const int overShootingShadowScaleHeightLimit = 64 * 3;
 619         private const int overShootingShadowAnimationDuration = 300;
 620         private Animation overShootingShadowAnimation;
 621         private bool isOverShootingShadowShown = false;
 622         private float startShowShadowDisplacement;
 623
 624         /// <summary>
 625         /// Default Constructor
 626         /// </summary>
 627         /// <since_tizen> 8 </since_tizen>
 628         public ScrollableBase() : base()
 629         {
 630             DecelerationRate = 0.998f;
 631
 632             base.Layout = new ScrollableBaseCustomLayout();
 633             mPanGestureDetector = new PanGestureDetector();
 634             mPanGestureDetector.Attach(this);
 635             mPanGestureDetector.AddDirection(PanGestureDetector.DirectionVertical);
 636             if (mPanGestureDetector.GetMaximumTouchesRequired() < 2) mPanGestureDetector.SetMaximumTouchesRequired(2);
 637             mPanGestureDetector.Detected += OnPanGestureDetected;
 638
 639             ClippingMode = ClippingModeType.ClipToBoundingBox;
 640
 641             //Default Scrolling child
 642             ContentContainer = new View()
 643             {
 644                 Name = "ContentContainer",
 645                 WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent,
 646                 HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent,
 647             };
 648             ContentContainer.Relayout += OnScrollingChildRelayout;
 649             propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(mScrollingEventThreshold));
 650             propertyNotification.Notified += OnPropertyChanged;
 651             base.Add(ContentContainer);
 652
 653             Scrollbar = new Scrollbar();
 654
 655             //Show vertical shadow on the top (or bottom) of the scrollable when panning down (or up).
 656             topOverShootingShadowView = new View
 657             {
 658                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_top.png",
 659                 Opacity = 1.0f,
 660                 SizeHeight = 0.0f,
 661                 PositionUsesPivotPoint = true,
 662                 ParentOrigin = NUI.ParentOrigin.TopCenter,
 663                 PivotPoint = NUI.PivotPoint.TopCenter,
 664             };
 665             bottomOverShootingShadowView = new View
 666             {
 667                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_bottom.png",
 668                 Opacity = 1.0f,
 669                 SizeHeight = 0.0f,
 670                 PositionUsesPivotPoint = true,
 671                 ParentOrigin = NUI.ParentOrigin.BottomCenter,
 672                 PivotPoint = NUI.PivotPoint.BottomCenter,
 673             };
 674             //Show horizontal shadow on the left (or right) of the scrollable when panning down (or up).
 675             leftOverShootingShadowView = new View
 676             {
 677                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_left.png",
 678                 Opacity = 1.0f,
 679                 SizeWidth = 0.0f,
 680                 PositionUsesPivotPoint = true,
 681                 ParentOrigin = NUI.ParentOrigin.CenterLeft,
 682                 PivotPoint = NUI.PivotPoint.CenterLeft,
 683             };
 684             rightOverShootingShadowView = new View
 685             {
 686                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_right.png",
 687                 Opacity = 1.0f,
 688                 SizeWidth = 0.0f,
 689                 PositionUsesPivotPoint = true,
 690                 ParentOrigin = NUI.ParentOrigin.CenterRight,
 691                 PivotPoint = NUI.PivotPoint.CenterRight,
 692             };
 693
 694             AccessibilityManager.Instance.SetAccessibilityAttribute(this, AccessibilityManager.AccessibilityAttribute.Trait, "ScrollableBase");
 695
 696             SetKeyboardNavigationSupport(true);
 697         }
 698
 699         private bool OnInterruptTouchingChildTouched(object source, View.TouchEventArgs args)
 700         {
 701             if (args.Touch.GetState(0) == PointStateType.Down)
 702             {
 703                 if (scrolling && !SnapToPage)
 704                 {
 705                     StopScroll();
 706                 }
 707             }
 708             return true;
 709         }
 710
 711         private void OnPropertyChanged(object source, PropertyNotification.NotifyEventArgs args)
 712         {
 713             OnScroll();
 714         }
 715
 716         /// <summary>
 717         /// Called after a child has been added to the owning view.
 718         /// </summary>
 719         /// <param name="view">The child which has been added.</param>
 720         /// <since_tizen> 8 </since_tizen>
 721         public override void Add(View view)
 722         {
 723             ContentContainer.Add(view);
 724         }
 725
 726         /// <summary>
 727         /// Called after a child has been removed from the owning view.
 728         /// </summary>
 729         /// <param name="view">The child which has been removed.</param>
 730         /// <since_tizen> 8 </since_tizen>
 731         public override void Remove(View view)
 732         {
 733             if (SnapToPage && CurrentPage == Children.IndexOf(view) && CurrentPage == Children.Count - 1 && Children.Count > 1)
 734             {
 735                 // Target View is current page and also last child.
 736                 // CurrentPage should be changed to previous page.
 737                 ScrollToIndex(CurrentPage - 1);
 738             }
 739
 740             ContentContainer.Remove(view);
 741         }
 742
 743         private void OnScrollingChildRelayout(object source, EventArgs args)
 744         {
 745             // Size is changed. Calculate maxScrollDistance.
 746             bool isSizeChanged = previousContainerSize.Width != ContentContainer.Size.Width || previousContainerSize.Height != ContentContainer.Size.Height ||
 747                 previousSize.Width != Size.Width || previousSize.Height != Size.Height;
 748
 749             if (isSizeChanged)
 750             {
 751                 maxScrollDistance = CalculateMaximumScrollDistance();
 752                 if (!ReviseContainerPositionIfNeed())
 753                 {
 754                     UpdateScrollbar();
 755                 }
 756             }
 757
 758             previousContainerSize = ContentContainer.Size;
 759             previousSize = Size;
 760         }
 761
 762         private bool ReviseContainerPositionIfNeed()
 763         {
 764             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 765             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 766
 767             if (Math.Abs(currentPosition) > maxScrollDistance)
 768             {
 769                 StopScroll();
 770                 var targetPosition = BoundScrollPosition(-maxScrollDistance);
 771                 if (isHorizontal) ContentContainer.PositionX = targetPosition;
 772                 else ContentContainer.PositionY = targetPosition;
 773                 return true;
 774             }
 775
 776             return false;
 777         }
 778
 779         /// <summary>
 780         /// The composition of a Scrollbar can vary depending on how you use ScrollableBase.
 781         /// Set the composition that will go into the ScrollableBase according to your ScrollableBase.
 782         /// </summary>
 783         /// <since_tizen> 8 </since_tizen>
 784         [EditorBrowsable(EditorBrowsableState.Never)]
 785         protected virtual void SetScrollbar()
 786         {
 787             if (Scrollbar)
 788             {
 789                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 790                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 791                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 792                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 793                 Scrollbar.Initialize(contentLength, viewportLength, -currentPosition, isHorizontal);
 794             }
 795         }
 796
 797         /// Update scrollbar position and size.
 798         [EditorBrowsable(EditorBrowsableState.Never)]
 799         protected virtual void UpdateScrollbar()
 800         {
 801             if (Scrollbar)
 802             {
 803                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 804                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 805                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 806                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 807                 Scrollbar.Update(contentLength, viewportLength, -currentPosition);
 808             }
 809         }
 810
 811         /// <summary>
 812         /// Scrolls to the item at the specified index.
 813         /// </summary>
 814         /// <param name="index">Index of item.</param>
 815         /// <since_tizen> 8 </since_tizen>
 816         public void ScrollToIndex(int index)
 817         {
 818             if (ContentContainer.ChildCount - 1 < index || index < 0)
 819             {
 820                 return;
 821             }
 822
 823             if (SnapToPage)
 824             {
 825                 CurrentPage = index;
 826             }
 827
 828             float targetPosition = Math.Min(ScrollingDirection == Direction.Vertical ? Children[index].Position.Y : Children[index].Position.X, maxScrollDistance);
 829             AnimateChildTo(ScrollDuration, -targetPosition);
 830         }
 831
 832         private void OnScrollDragStarted()
 833         {
 834             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 835             ScrollDragStarted?.Invoke(this, eventArgs);
 836         }
 837
 838         private void OnScrollDragEnded()
 839         {
 840             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 841             ScrollDragEnded?.Invoke(this, eventArgs);
 842         }
 843
 844         private void OnScrollAnimationStarted()
 845         {
 846             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 847             ScrollAnimationStarted?.Invoke(this, eventArgs);
 848         }
 849
 850         private void OnScrollAnimationEnded()
 851         {
 852             scrolling = false;
 853             this.InterceptTouchEvent -= OnInterruptTouchingChildTouched;
 854
 855             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 856             ScrollAnimationEnded?.Invoke(this, eventArgs);
 857         }
 858
 859         private void OnScroll()
 860         {
 861             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 862             Scrolling?.Invoke(this, eventArgs);
 863
 864             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 865             float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 866             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 867
 868             scrollBar?.Update(contentLength, Math.Abs(currentPosition));
 869             CheckPreReachedTargetPosition();
 870         }
 871
 872         private void CheckPreReachedTargetPosition()
 873         {
 874             // Check whether we reached pre-reached target position
 875             if (readyToNotice &&
 876                 ContentContainer.CurrentPosition.Y <= finalTargetPosition + NoticeAnimationEndBeforePosition &&
 877                 ContentContainer.CurrentPosition.Y >= finalTargetPosition - NoticeAnimationEndBeforePosition)
 878             {
 879                 //Notice first
 880                 readyToNotice = false;
 881                 OnPreReachedTargetPosition(finalTargetPosition);
 882             }
 883         }
 884
 885         /// <summary>
 886         /// This helps developer who wants to know before scroll is reaching target position.
 887         /// </summary>
 888         /// <param name="targetPosition">Index of item.</param>
 889         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
 890         [EditorBrowsable(EditorBrowsableState.Never)]
 891         protected virtual void OnPreReachedTargetPosition(float targetPosition)
 892         {
 893
 894         }
 895
 896         private void StopScroll()
 897         {
 898             if (scrollAnimation != null)
 899             {
 900                 if (scrollAnimation.State == Animation.States.Playing)
 901                 {
 902                     Debug.WriteLineIf(LayoutDebugScrollableBase, "StopScroll Animation Playing");
 903                     scrollAnimation.Stop(Animation.EndActions.Cancel);
 904                     OnScrollAnimationEnded();
 905                 }
 906                 scrollAnimation.Clear();
 907             }
 908         }
 909
 910         private void AnimateChildTo(int duration, float axisPosition)
 911         {
 912             Debug.WriteLineIf(LayoutDebugScrollableBase, "AnimationTo Animation Duration:" + duration + " Destination:" + axisPosition);
 913             finalTargetPosition = axisPosition;
 914
 915             StopScroll(); // Will replace previous animation so will stop existing one.
 916
 917             if (scrollAnimation == null)
 918             {
 919                 scrollAnimation = new Animation();
 920                 scrollAnimation.Finished += ScrollAnimationFinished;
 921             }
 922
 923             scrollAnimation.Duration = duration;
 924             scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.EaseOutSquare);
 925             scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", axisPosition, ScrollAlphaFunction);
 926             scrolling = true;
 927             OnScrollAnimationStarted();
 928             scrollAnimation.Play();
 929         }
 930
 931         /// <summary>
 932         /// Scroll to specific position with or without animation.
 933         /// </summary>
 934         /// <param name="position">Destination.</param>
 935         /// <param name="animate">Scroll with or without animation</param>
 936         /// <since_tizen> 8 </since_tizen>
 937         public void ScrollTo(float position, bool animate)
 938         {
 939             StopScroll();
 940             float currentPositionX = ContentContainer.CurrentPosition.X != 0 ? ContentContainer.CurrentPosition.X : ContentContainer.Position.X;
 941             float currentPositionY = ContentContainer.CurrentPosition.Y != 0 ? ContentContainer.CurrentPosition.Y : ContentContainer.Position.Y;
 942             float delta = ScrollingDirection == Direction.Horizontal ? currentPositionX : currentPositionY;
 943             // The argument position is the new pan position. So the new position of ScrollableBase becomes (-position).
 944             // To move ScrollableBase's position to (-position), it moves by (-position - currentPosition).
 945             delta = -position - delta;
 946
 947             ScrollBy(delta, animate);
 948         }
 949
 950         private float BoundScrollPosition(float targetPosition)
 951         {
 952             if (ScrollAvailableArea != null)
 953             {
 954                 float minScrollPosition = ScrollAvailableArea.X;
 955                 float maxScrollPosition = ScrollAvailableArea.Y;
 956
 957                 targetPosition = Math.Min(-minScrollPosition, targetPosition);
 958                 targetPosition = Math.Max(-maxScrollPosition, targetPosition);
 959             }
 960             else
 961             {
 962                 targetPosition = Math.Min(0, targetPosition);
 963                 targetPosition = Math.Max(-maxScrollDistance, targetPosition);
 964             }
 965
 966             return targetPosition;
 967         }
 968
 969         private void ScrollBy(float displacement, bool animate)
 970         {
 971             if (GetChildCount() == 0 || maxScrollDistance < 0)
 972             {
 973                 return;
 974             }
 975
 976             float childCurrentPosition = (ScrollingDirection == Direction.Horizontal) ? ContentContainer.PositionX : ContentContainer.PositionY;
 977
 978             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy childCurrentPosition:" + childCurrentPosition +
 979                 " displacement:" + displacement,
 980                 " maxScrollDistance:" + maxScrollDistance);
 981
 982             childTargetPosition = childCurrentPosition + displacement; // child current position + gesture displacement
 983
 984             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy currentAxisPosition:" + childCurrentPosition + "childTargetPosition:" + childTargetPosition);
 985
 986             if (animate)
 987             {
 988                 // Calculate scroll animation duration
 989                 float scrollDistance = Math.Abs(displacement);
 990                 readyToNotice = true;
 991
 992                 AnimateChildTo(ScrollDuration, BoundScrollPosition(AdjustTargetPositionOfScrollAnimation(BoundScrollPosition(childTargetPosition))));
 993             }
 994             else
 995             {
 996                 StopScroll();
 997                 finalTargetPosition = BoundScrollPosition(childTargetPosition);
 998
 999                 // Set position of scrolling child without an animation
1000                 if (ScrollingDirection == Direction.Horizontal)
1001                 {
1002                     ContentContainer.PositionX = finalTargetPosition;
1003                 }
1004                 else
1005                 {
1006                     ContentContainer.PositionY = finalTargetPosition;
1007                 }
1008             }
1009         }
1010
1011         /// <summary>
1012         /// you can override it to clean-up your own resources.
1013         /// </summary>
1014         /// <param name="type">DisposeTypes</param>
1015         /// This will be public opened in tizen_5.5 after ACR done. Before ACR, need to be hidden as inhouse API.
1016         [EditorBrowsable(EditorBrowsableState.Never)]
1017         protected override void Dispose(DisposeTypes type)
1018         {
1019             if (disposed)
1020             {
1021                 return;
1022             }
1023
1024             if (type == DisposeTypes.Explicit)
1025             {
1026                 StopOverShootingShadowAnimation();
1027                 StopScroll();
1028
1029                 if (mPanGestureDetector != null)
1030                 {
1031                     mPanGestureDetector.Detected -= OnPanGestureDetected;
1032                     mPanGestureDetector.Dispose();
1033                     mPanGestureDetector = null;
1034                 }
1035
1036                 propertyNotification.Dispose();
1037             }
1038             base.Dispose(type);
1039         }
1040
1041         private float CalculateMaximumScrollDistance()
1042         {
1043             float scrollingChildLength = 0;
1044             float scrollerLength = 0;
1045             if (ScrollingDirection == Direction.Horizontal)
1046             {
1047                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Horizontal");
1048
1049                 scrollingChildLength = ContentContainer.Size.Width;
1050                 scrollerLength = Size.Width;
1051             }
1052             else
1053             {
1054                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Vertical");
1055                 scrollingChildLength = ContentContainer.Size.Height;
1056                 scrollerLength = Size.Height;
1057             }
1058
1059             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy maxScrollDistance:" + (scrollingChildLength - scrollerLength) +
1060                 " parent length:" + scrollerLength +
1061                 " scrolling child length:" + scrollingChildLength);
1062
1063             return Math.Max(scrollingChildLength - scrollerLength, 0);
1064         }
1065
1066         private void PageSnap(float velocity)
1067         {
1068             float destination;
1069
1070             Debug.WriteLineIf(LayoutDebugScrollableBase, "PageSnap with pan candidate totalDisplacement:" + totalDisplacementForPan +
1071                 " currentPage[" + CurrentPage + "]");
1072
1073             //Increment current page if total displacement enough to warrant a page change.
1074             if (Math.Abs(totalDisplacementForPan) > (mPageWidth * ratioOfScreenWidthToCompleteScroll))
1075             {
1076                 if (totalDisplacementForPan < 0)
1077                 {
1078                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1079                 }
1080                 else
1081                 {
1082                     CurrentPage = Math.Max(0, --CurrentPage);
1083                 }
1084             }
1085             else if (Math.Abs(velocity) > PageFlickThreshold)
1086             {
1087                 if (velocity < 0)
1088                 {
1089                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1090                 }
1091                 else
1092                 {
1093                     CurrentPage = Math.Max(0, --CurrentPage);
1094                 }
1095             }
1096
1097             // Animate to new page or reposition to current page
1098             if (ScrollingDirection == Direction.Horizontal)
1099                 destination = -(Children[CurrentPage].Position.X + Children[CurrentPage].CurrentSize.Width / 2 - CurrentSize.Width / 2); // set to middle of current page
1100             else
1101                 destination = -(Children[CurrentPage].Position.Y + Children[CurrentPage].CurrentSize.Height / 2 - CurrentSize.Height / 2);
1102
1103             AnimateChildTo(ScrollDuration, destination);
1104         }
1105
1106         /// <summary>
1107         /// Enable/Disable overshooting effect. default is disabled.
1108         /// </summary>
1109         [EditorBrowsable(EditorBrowsableState.Never)]
1110         public bool EnableOverShootingEffect { get; set; } = false;
1111
1112         private void AttachOverShootingShadowView()
1113         {
1114             if (!EnableOverShootingEffect)
1115                 return;
1116
1117             // stop animation if necessary.
1118             StopOverShootingShadowAnimation();
1119
1120             if (ScrollingDirection == Direction.Horizontal)
1121             {
1122                 base.Add(leftOverShootingShadowView);
1123                 base.Add(rightOverShootingShadowView);
1124
1125                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1126                 leftOverShootingShadowView.Opacity = 1.0f;
1127                 leftOverShootingShadowView.RaiseToTop();
1128
1129                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1130                 rightOverShootingShadowView.Opacity = 1.0f;
1131                 rightOverShootingShadowView.RaiseToTop();
1132             }
1133             else
1134             {
1135                 base.Add(topOverShootingShadowView);
1136                 base.Add(bottomOverShootingShadowView);
1137
1138                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1139                 topOverShootingShadowView.Opacity = 1.0f;
1140                 topOverShootingShadowView.RaiseToTop();
1141
1142                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1143                 bottomOverShootingShadowView.Opacity = 1.0f;
1144                 bottomOverShootingShadowView.RaiseToTop();
1145             }
1146
1147             // at the beginning, height or width of overshooting shadow is 0, so it is invisible.
1148             isOverShootingShadowShown = false;
1149         }
1150
1151         private void DragOverShootingShadow(float totalPanDisplacement, float panDisplacement)
1152         {
1153             if (!EnableOverShootingEffect)
1154                 return;
1155
1156             if (totalPanDisplacement > 0) // downwards
1157             {
1158                 // check if reaching at the top / left.
1159                 if ((int)finalTargetPosition != 0)
1160                 {
1161                     isOverShootingShadowShown = false;
1162                     return;
1163                 }
1164
1165                 // save start displacement, and re-calculate displacement.
1166                 if (!isOverShootingShadowShown)
1167                 {
1168                     startShowShadowDisplacement = totalPanDisplacement;
1169                 }
1170                 isOverShootingShadowShown = true;
1171
1172                 float newDisplacement = (int)totalPanDisplacement < (int)startShowShadowDisplacement ? 0 : totalPanDisplacement - startShowShadowDisplacement;
1173
1174                 if (ScrollingDirection == Direction.Horizontal)
1175                 {
1176                     // scale limit of height is 60%.
1177                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1178                     leftOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1179
1180                     // scale limit of width is 300%.
1181                     leftOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1182
1183                     // trigger event
1184                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1185                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1186                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1187                 }
1188                 else
1189                 {
1190                     // scale limit of width is 60%.
1191                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1192                     topOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1193
1194                     // scale limit of height is 300%.
1195                     topOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1196
1197                     // trigger event
1198                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1199                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1200                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1201                 }
1202             }
1203             else if (totalPanDisplacement < 0) // upwards
1204             {
1205                 // check if reaching at the bottom.
1206                 if (-(int)finalTargetPosition != (int)maxScrollDistance)
1207                 {
1208                     isOverShootingShadowShown = false;
1209                     return;
1210                 }
1211
1212                 // save start displacement, and re-calculate displacement.
1213                 if (!isOverShootingShadowShown)
1214                 {
1215                     startShowShadowDisplacement = totalPanDisplacement;
1216                 }
1217                 isOverShootingShadowShown = true;
1218
1219                 float newDisplacement = (int)startShowShadowDisplacement < (int)totalPanDisplacement ? 0 : startShowShadowDisplacement - totalPanDisplacement;
1220
1221                 if (ScrollingDirection == Direction.Horizontal)
1222                 {
1223                     // scale limit of height is 60%.
1224                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1225                     rightOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1226
1227                     // scale limit of width is 300%.
1228                     rightOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1229
1230                     // trigger event
1231                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1232                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1233                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1234                 }
1235                 else
1236                 {
1237                     // scale limit of width is 60%.
1238                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1239                     bottomOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1240
1241                     // scale limit of height is 300%.
1242                     bottomOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1243
1244                     // trigger event
1245                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1246                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1247                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1248                 }
1249             }
1250             else
1251             {
1252                 // if total displacement is 0, shadow would become invisible.
1253                 isOverShootingShadowShown = false;
1254             }
1255         }
1256
1257         private void PlayOverShootingShadowAnimation()
1258         {
1259             if (!EnableOverShootingEffect)
1260                 return;
1261
1262             // stop animation if necessary.
1263             StopOverShootingShadowAnimation();
1264
1265             if (overShootingShadowAnimation == null)
1266             {
1267                 overShootingShadowAnimation = new Animation(overShootingShadowAnimationDuration);
1268                 overShootingShadowAnimation.Finished += OnOverShootingShadowAnimationFinished;
1269             }
1270
1271             if (ScrollingDirection == Direction.Horizontal)
1272             {
1273                 View targetView = totalDisplacementForPan < 0 ? rightOverShootingShadowView : leftOverShootingShadowView;
1274                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", SizeHeight);
1275                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", 0.0f);
1276                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1277             }
1278             else
1279             {
1280                 View targetView = totalDisplacementForPan < 0 ? bottomOverShootingShadowView : topOverShootingShadowView;
1281                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", SizeWidth);
1282                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", 0.0f);
1283                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1284             }
1285             overShootingShadowAnimation.Play();
1286         }
1287
1288         private void StopOverShootingShadowAnimation()
1289         {
1290             if (overShootingShadowAnimation == null || overShootingShadowAnimation.State != Animation.States.Playing)
1291                 return;
1292
1293             overShootingShadowAnimation.Stop(Animation.EndActions.Cancel);
1294             OnOverShootingShadowAnimationFinished(null, null);
1295             overShootingShadowAnimation.Clear();
1296         }
1297
1298         private void OnOverShootingShadowAnimationFinished(object sender, EventArgs e)
1299         {
1300             if (ScrollingDirection == Direction.Horizontal)
1301             {
1302                 base.Remove(leftOverShootingShadowView);
1303                 base.Remove(rightOverShootingShadowView);
1304
1305                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1306                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1307             }
1308             else
1309             {
1310                 base.Remove(topOverShootingShadowView);
1311                 base.Remove(bottomOverShootingShadowView);
1312
1313                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1314                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1315             }
1316
1317             // after animation finished, height/width & opacity of vertical shadow both are 0, so it is invisible.
1318             isOverShootingShadowShown = false;
1319         }
1320
1321         private void OnScrollOutOfBound(ScrollOutOfBoundEventArgs.Direction direction, float displacement)
1322         {
1323             ScrollOutOfBoundEventArgs args = new ScrollOutOfBoundEventArgs(direction, displacement);
1324             ScrollOutOfBound?.Invoke(this, args);
1325         }
1326
1327         private void OnPanGestureDetected(object source, PanGestureDetector.DetectedEventArgs e)
1328         {
1329             OnPanGesture(e.PanGesture);
1330             if(!((SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing) || e.PanGesture.State == Gesture.StateType.Started))
1331             {
1332                 e.Handled = !((int)finalTargetPosition == 0 || -(int)finalTargetPosition == (int)maxScrollDistance);
1333             }
1334         }
1335
1336         private void OnPanGesture(PanGesture panGesture)
1337         {
1338             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1339             {
1340                 return;
1341             }
1342
1343             if (panGesture.State == Gesture.StateType.Started)
1344             {
1345                 readyToNotice = false;
1346                 //Interrupt touching when panning is started
1347                 this.InterceptTouchEvent += OnInterruptTouchingChildTouched;
1348                 AttachOverShootingShadowView();
1349                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Gesture Start");
1350                 if (scrolling && !SnapToPage)
1351                 {
1352                     StopScroll();
1353                 }
1354                 totalDisplacementForPan = 0.0f;
1355                 OnScrollDragStarted();
1356             }
1357             else if (panGesture.State == Gesture.StateType.Continuing)
1358             {
1359                 if (ScrollingDirection == Direction.Horizontal)
1360                 {
1361                     // if vertical shadow is shown, does not scroll.
1362                     if (!isOverShootingShadowShown)
1363                     {
1364                         ScrollBy(panGesture.Displacement.X, false);
1365                     }
1366                     totalDisplacementForPan += panGesture.Displacement.X;
1367                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.X);
1368                 }
1369                 else
1370                 {
1371                     // if vertical shadow is shown, does not scroll.
1372                     if (!isOverShootingShadowShown)
1373                     {
1374                         ScrollBy(panGesture.Displacement.Y, false);
1375                     }
1376                     totalDisplacementForPan += panGesture.Displacement.Y;
1377                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.Y);
1378                 }
1379                 Debug.WriteLineIf(LayoutDebugScrollableBase, "OnPanGestureDetected Continue totalDisplacementForPan:" + totalDisplacementForPan);
1380
1381             }
1382             else if (panGesture.State == Gesture.StateType.Finished || panGesture.State == Gesture.StateType.Cancelled)
1383             {
1384                 PlayOverShootingShadowAnimation();
1385                 OnScrollDragEnded();
1386                 StopScroll(); // Will replace previous animation so will stop existing one.
1387
1388                 if (scrollAnimation == null)
1389                 {
1390                     scrollAnimation = new Animation();
1391                     scrollAnimation.Finished += ScrollAnimationFinished;
1392                 }
1393
1394                 float panVelocity = (ScrollingDirection == Direction.Horizontal) ? panGesture.Velocity.X : panGesture.Velocity.Y;
1395
1396                 if (SnapToPage)
1397                 {
1398                     PageSnap(panVelocity);
1399                 }
1400                 else
1401                 {
1402                     if (panVelocity == 0)
1403                     {
1404                         float currentScrollPosition = (ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1405                         scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
1406                         scrollAnimation.Duration = 0;
1407                         scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", currentScrollPosition);
1408                         scrollAnimation.Play();
1409                     }
1410                     else
1411                     {
1412                         Decelerating(panVelocity, scrollAnimation);
1413                     }
1414                 }
1415
1416                 totalDisplacementForPan = 0;
1417                 scrolling = true;
1418                 readyToNotice = true;
1419                 OnScrollAnimationStarted();
1420             }
1421         }
1422
1423         internal void BaseRemove(View view)
1424         {
1425             base.Remove(view);
1426         }
1427
1428         internal override bool OnAccessibilityPan(PanGesture gestures)
1429         {
1430             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1431             {
1432                 return false;
1433             }
1434
1435             OnPanGesture(gestures);
1436             return true;
1437         }
1438
1439         private float CustomScrollAlphaFunction(float progress)
1440         {
1441             if (panAnimationDelta == 0)
1442             {
1443                 return 1.0f;
1444             }
1445             else
1446             {
1447                 // Parameter "progress" is normalized value. We need to multiply target duration to calculate distance.
1448                 // Can get real distance using equation of deceleration (check Decelerating function)
1449                 // After get real distance, normalize it
1450                 float realDuration = progress * panAnimationDuration;
1451                 float realDistance = velocityOfLastPan * ((float)Math.Pow(decelerationRate, realDuration) - 1) / logValueOfDeceleration;
1452                 float result = Math.Min(realDistance / Math.Abs(panAnimationDelta), 1.0f);
1453                 return result;
1454             }
1455         }
1456
1457         /// <summary>
1458         /// you can override it to custom your decelerating
1459         /// </summary>
1460         /// <param name="velocity">Velocity of current pan.</param>
1461         /// <param name="animation">Scroll animation.</param>
1462         [EditorBrowsable(EditorBrowsableState.Never)]
1463         protected virtual void Decelerating(float velocity, Animation animation)
1464         {
1465             // Decelerating using deceleration equation ===========
1466             //
1467             // V   : velocity (pixel per millisecond)
1468             // V0  : initial velocity
1469             // d   : deceleration rate,
1470             // t   : time
1471             // X   : final position after decelerating
1472             // log : natural logarithm
1473             //
1474             // V(t) = V0 * d pow t;
1475             // X(t) = V0 * (d pow t - 1) / log d;  <-- Integrate the velocity function
1476             // X(∞) = V0 * d / (1 - d); <-- Result using infinite T can be final position because T is tending to infinity.
1477             //
1478             // Because of final T is tending to infinity, we should use threshold value to finish.
1479             // Final T = log(-threshold * log d / |V0| ) / log d;
1480
1481             velocityOfLastPan = Math.Abs(velocity);
1482
1483             float currentScrollPosition = -(ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1484             panAnimationDelta = (velocityOfLastPan * decelerationRate) / (1 - decelerationRate);
1485             panAnimationDelta = velocity > 0 ? -panAnimationDelta : panAnimationDelta;
1486
1487             float destination = -(panAnimationDelta + currentScrollPosition);
1488             float adjustDestination = AdjustTargetPositionOfScrollAnimation(destination);
1489             float maxPosition = ScrollAvailableArea != null ? ScrollAvailableArea.Y : maxScrollDistance;
1490             float minPosition = ScrollAvailableArea != null ? ScrollAvailableArea.X : 0;
1491
1492             if (destination < -maxPosition || destination > minPosition)
1493             {
1494                 panAnimationDelta = velocity > 0 ? (currentScrollPosition - minPosition) : (maxPosition - currentScrollPosition);
1495                 destination = velocity > 0 ? minPosition : -maxPosition;
1496
1497                 if (panAnimationDelta == 0)
1498                 {
1499                     panAnimationDuration = 0.0f;
1500                 }
1501                 else
1502                 {
1503                     panAnimationDuration = (float)Math.Log((panAnimationDelta * logValueOfDeceleration / velocityOfLastPan + 1), decelerationRate);
1504                 }
1505
1506                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1507                     "OverRange======================= \n" +
1508                     "[decelerationRate] " + decelerationRate + "\n" +
1509                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1510                     "[Velocity] " + velocityOfLastPan + "\n" +
1511                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1512                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1513                     "[Destination] " + destination + "\n" +
1514                     "[Duration] " + panAnimationDuration + "\n" +
1515                     "================================ \n"
1516                 );
1517             }
1518             else
1519             {
1520                 panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1521
1522                 if (adjustDestination != destination)
1523                 {
1524                     destination = adjustDestination;
1525                     panAnimationDelta = destination + currentScrollPosition;
1526                     velocityOfLastPan = Math.Abs(panAnimationDelta * logValueOfDeceleration / ((float)Math.Pow(decelerationRate, panAnimationDuration) - 1));
1527                     panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1528                 }
1529
1530                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1531                     "================================ \n" +
1532                     "[decelerationRate] " + decelerationRate + "\n" +
1533                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1534                     "[Velocity] " + velocityOfLastPan + "\n" +
1535                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1536                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1537                     "[Destination] " + destination + "\n" +
1538                     "[Duration] " + panAnimationDuration + "\n" +
1539                     "================================ \n"
1540                 );
1541             }
1542
1543             finalTargetPosition = destination;
1544
1545             customScrollAlphaFunction = new UserAlphaFunctionDelegate(CustomScrollAlphaFunction);
1546             animation.DefaultAlphaFunction = new AlphaFunction(customScrollAlphaFunction);
1547             GC.KeepAlive(customScrollAlphaFunction);
1548             animation.Duration = (int)panAnimationDuration;
1549             animation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", destination);
1550             animation.Play();
1551         }
1552
1553         private void ScrollAnimationFinished(object sender, EventArgs e)
1554         {
1555             OnScrollAnimationEnded();
1556         }
1557
1558         /// <summary>
1559         /// Adjust scrolling position by own scrolling rules.
1560         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1561         /// </summary>
1562         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
1563         [EditorBrowsable(EditorBrowsableState.Never)]
1564         protected virtual float AdjustTargetPositionOfScrollAnimation(float position)
1565         {
1566             return position;
1567         }
1568
1569         /// <summary>
1570         /// Scroll position given to ScrollTo.
1571         /// This is the position in the opposite direction to the position of ContentContainer.
1572         /// </summary>
1573         /// <since_tizen> 8 </since_tizen>
1574         public Position ScrollPosition
1575         {
1576             get
1577             {
1578                 return new Position(-ContentContainer.Position);
1579             }
1580         }
1581
1582         /// <summary>
1583         /// Current scroll position in the middle of ScrollTo animation.
1584         /// This is the position in the opposite direction to the current position of ContentContainer.
1585         /// </summary>
1586         /// <since_tizen> 8 </since_tizen>
1587         public Position ScrollCurrentPosition
1588         {
1589             get
1590             {
1591                 return new Position(-ContentContainer.CurrentPosition);
1592             }
1593         }
1594
1595         /// <summary>
1596         /// Remove all children in ContentContainer.
1597         /// </summary>
1598         /// <param name="dispose">If true, removed child is disposed.</param>
1599         [EditorBrowsable(EditorBrowsableState.Never)]
1600         public void RemoveAllChildren(bool dispose = false)
1601         {
1602             RecursiveRemoveChildren(ContentContainer, dispose);
1603         }
1604
1605         private void RecursiveRemoveChildren(View parent, bool dispose)
1606         {
1607             if (parent == null)
1608             {
1609                 return;
1610             }
1611             int maxChild = (int)parent.GetChildCount();
1612             for (int i = maxChild - 1; i >= 0; --i)
1613             {
1614                 View child = parent.GetChildAt((uint)i);
1615                 if (child == null)
1616                 {
1617                     continue;
1618                 }
1619                 RecursiveRemoveChildren(child, dispose);
1620                 parent.Remove(child);
1621                 if (dispose)
1622                 {
1623                     child.Dispose();
1624                 }
1625             }
1626         }
1627
1628
1629         /// <inheritdoc/>
1630         [EditorBrowsable(EditorBrowsableState.Never)]
1631         public override View GetNextFocusableView(View currentFocusedView, View.FocusDirection direction, bool loopEnabled)
1632         {
1633             View nextFocusedView = null;
1634
1635             int currentIndex = ContentContainer.Children.IndexOf(currentFocusedView);
1636
1637             switch (direction)
1638             {
1639                 case View.FocusDirection.Left:
1640                 case View.FocusDirection.Up:
1641                 {
1642                     if (currentIndex > 0)
1643                     {
1644                         nextFocusedView = ContentContainer.Children[--currentIndex];
1645                     }
1646                     break;
1647                 }
1648                 case View.FocusDirection.Right:
1649                 case View.FocusDirection.Down:
1650                 {
1651                     if (currentIndex < ContentContainer.Children.Count - 1)
1652                     {
1653                         nextFocusedView =  ContentContainer.Children[++currentIndex];
1654                     }
1655                     break;
1656                 }
1657             }
1658
1659             if (nextFocusedView != null)
1660             {
1661                 // Check next focused view is inside of visible area.
1662                 // If it is not, move scroll position to make it visible.
1663                 Position scrollPosition = ContentContainer.CurrentPosition;
1664                 float targetPosition = -(ScrollingDirection == Direction.Horizontal ? scrollPosition.X : scrollPosition.Y);
1665
1666                 float left = nextFocusedView.Position.X;
1667                 float right = nextFocusedView.Position.X + nextFocusedView.Size.Width;
1668                 float top = nextFocusedView.Position.Y;
1669                 float bottom = nextFocusedView.Position.Y + nextFocusedView.Size.Height;
1670
1671                 float visibleRectangleLeft = -scrollPosition.X;
1672                 float visibleRectangleRight = -scrollPosition.X + Size.Width;
1673                 float visibleRectangleTop = -scrollPosition.Y;
1674                 float visibleRectangleBottom = -scrollPosition.Y + Size.Height;
1675
1676                 if (ScrollingDirection == Direction.Horizontal)
1677                 {
1678                     if (left < visibleRectangleLeft)
1679                     {
1680                         targetPosition = left;
1681                     }
1682                     else if (right > visibleRectangleRight)
1683                     {
1684                         targetPosition = right - Size.Width;
1685                     }
1686                 }
1687                 else
1688                 {
1689                     if (top < visibleRectangleTop)
1690                     {
1691                         targetPosition = top;
1692                     }
1693                     else if (bottom > visibleRectangleBottom)
1694                     {
1695                         targetPosition = bottom - Size.Height;
1696                     }
1697                 }
1698                 ScrollTo(targetPosition, true);
1699             }
1700
1701             return nextFocusedView;
1702         }
1703     }
1704
1705 } // namespace