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
 697         private bool OnInterruptTouchingChildTouched(object source, View.TouchEventArgs args)
 698         {
 699             if (args.Touch.GetState(0) == PointStateType.Down)
 700             {
 701                 if (scrolling && !SnapToPage)
 702                 {
 703                     StopScroll();
 704                 }
 705             }
 706             return true;
 707         }
 708
 709         private void OnPropertyChanged(object source, PropertyNotification.NotifyEventArgs args)
 710         {
 711             OnScroll();
 712         }
 713
 714         /// <summary>
 715         /// Called after a child has been added to the owning view.
 716         /// </summary>
 717         /// <param name="view">The child which has been added.</param>
 718         /// <since_tizen> 8 </since_tizen>
 719         public override void Add(View view)
 720         {
 721             ContentContainer.Add(view);
 722         }
 723
 724         /// <summary>
 725         /// Called after a child has been removed from the owning view.
 726         /// </summary>
 727         /// <param name="view">The child which has been removed.</param>
 728         /// <since_tizen> 8 </since_tizen>
 729         public override void Remove(View view)
 730         {
 731             if (SnapToPage && CurrentPage == Children.IndexOf(view) && CurrentPage == Children.Count - 1 && Children.Count > 1)
 732             {
 733                 // Target View is current page and also last child.
 734                 // CurrentPage should be changed to previous page.
 735                 ScrollToIndex(CurrentPage - 1);
 736             }
 737
 738             ContentContainer.Remove(view);
 739         }
 740
 741         private void OnScrollingChildRelayout(object source, EventArgs args)
 742         {
 743             // Size is changed. Calculate maxScrollDistance.
 744             bool isSizeChanged = previousContainerSize.Width != ContentContainer.Size.Width || previousContainerSize.Height != ContentContainer.Size.Height ||
 745                 previousSize.Width != Size.Width || previousSize.Height != Size.Height;
 746
 747             if (isSizeChanged)
 748             {
 749                 maxScrollDistance = CalculateMaximumScrollDistance();
 750                 if (!ReviseContainerPositionIfNeed())
 751                 {
 752                     UpdateScrollbar();
 753                 }
 754             }
 755
 756             previousContainerSize = ContentContainer.Size;
 757             previousSize = Size;
 758         }
 759
 760         private bool ReviseContainerPositionIfNeed()
 761         {
 762             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 763             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 764
 765             if (Math.Abs(currentPosition) > maxScrollDistance)
 766             {
 767                 StopScroll();
 768                 var targetPosition = BoundScrollPosition(-maxScrollDistance);
 769                 if (isHorizontal) ContentContainer.PositionX = targetPosition;
 770                 else ContentContainer.PositionY = targetPosition;
 771                 return true;
 772             }
 773
 774             return false;
 775         }
 776
 777         /// <summary>
 778         /// The composition of a Scrollbar can vary depending on how you use ScrollableBase.
 779         /// Set the composition that will go into the ScrollableBase according to your ScrollableBase.
 780         /// </summary>
 781         /// <since_tizen> 8 </since_tizen>
 782         [EditorBrowsable(EditorBrowsableState.Never)]
 783         protected virtual void SetScrollbar()
 784         {
 785             if (Scrollbar)
 786             {
 787                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 788                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 789                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 790                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 791                 Scrollbar.Initialize(contentLength, viewportLength, -currentPosition, isHorizontal);
 792             }
 793         }
 794
 795         /// Update scrollbar position and size.
 796         [EditorBrowsable(EditorBrowsableState.Never)]
 797         protected virtual void UpdateScrollbar()
 798         {
 799             if (Scrollbar)
 800             {
 801                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 802                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 803                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 804                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 805                 Scrollbar.Update(contentLength, viewportLength, -currentPosition);
 806             }
 807         }
 808
 809         /// <summary>
 810         /// Scrolls to the item at the specified index.
 811         /// </summary>
 812         /// <param name="index">Index of item.</param>
 813         /// <since_tizen> 8 </since_tizen>
 814         public void ScrollToIndex(int index)
 815         {
 816             if (ContentContainer.ChildCount - 1 < index || index < 0)
 817             {
 818                 return;
 819             }
 820
 821             if (SnapToPage)
 822             {
 823                 CurrentPage = index;
 824             }
 825
 826             float targetPosition = Math.Min(ScrollingDirection == Direction.Vertical ? Children[index].Position.Y : Children[index].Position.X, maxScrollDistance);
 827             AnimateChildTo(ScrollDuration, -targetPosition);
 828         }
 829
 830         private void OnScrollDragStarted()
 831         {
 832             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 833             ScrollDragStarted?.Invoke(this, eventArgs);
 834         }
 835
 836         private void OnScrollDragEnded()
 837         {
 838             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 839             ScrollDragEnded?.Invoke(this, eventArgs);
 840         }
 841
 842         private void OnScrollAnimationStarted()
 843         {
 844             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 845             ScrollAnimationStarted?.Invoke(this, eventArgs);
 846         }
 847
 848         private void OnScrollAnimationEnded()
 849         {
 850             scrolling = false;
 851             this.InterceptTouchEvent -= OnInterruptTouchingChildTouched;
 852
 853             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 854             ScrollAnimationEnded?.Invoke(this, eventArgs);
 855         }
 856
 857         private void OnScroll()
 858         {
 859             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 860             Scrolling?.Invoke(this, eventArgs);
 861
 862             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 863             float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 864             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 865
 866             scrollBar?.Update(contentLength, Math.Abs(currentPosition));
 867             CheckPreReachedTargetPosition();
 868         }
 869
 870         private void CheckPreReachedTargetPosition()
 871         {
 872             // Check whether we reached pre-reached target position
 873             if (readyToNotice &&
 874                 ContentContainer.CurrentPosition.Y <= finalTargetPosition + NoticeAnimationEndBeforePosition &&
 875                 ContentContainer.CurrentPosition.Y >= finalTargetPosition - NoticeAnimationEndBeforePosition)
 876             {
 877                 //Notice first
 878                 readyToNotice = false;
 879                 OnPreReachedTargetPosition(finalTargetPosition);
 880             }
 881         }
 882
 883         /// <summary>
 884         /// This helps developer who wants to know before scroll is reaching target position.
 885         /// </summary>
 886         /// <param name="targetPosition">Index of item.</param>
 887         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
 888         [EditorBrowsable(EditorBrowsableState.Never)]
 889         protected virtual void OnPreReachedTargetPosition(float targetPosition)
 890         {
 891
 892         }
 893
 894         private void StopScroll()
 895         {
 896             if (scrollAnimation != null)
 897             {
 898                 if (scrollAnimation.State == Animation.States.Playing)
 899                 {
 900                     Debug.WriteLineIf(LayoutDebugScrollableBase, "StopScroll Animation Playing");
 901                     scrollAnimation.Stop(Animation.EndActions.Cancel);
 902                     OnScrollAnimationEnded();
 903                 }
 904                 scrollAnimation.Clear();
 905             }
 906         }
 907
 908         private void AnimateChildTo(int duration, float axisPosition)
 909         {
 910             Debug.WriteLineIf(LayoutDebugScrollableBase, "AnimationTo Animation Duration:" + duration + " Destination:" + axisPosition);
 911             finalTargetPosition = axisPosition;
 912
 913             StopScroll(); // Will replace previous animation so will stop existing one.
 914
 915             if (scrollAnimation == null)
 916             {
 917                 scrollAnimation = new Animation();
 918                 scrollAnimation.Finished += ScrollAnimationFinished;
 919             }
 920
 921             scrollAnimation.Duration = duration;
 922             scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.EaseOutSquare);
 923             scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", axisPosition, ScrollAlphaFunction);
 924             scrolling = true;
 925             OnScrollAnimationStarted();
 926             scrollAnimation.Play();
 927         }
 928
 929         /// <summary>
 930         /// Scroll to specific position with or without animation.
 931         /// </summary>
 932         /// <param name="position">Destination.</param>
 933         /// <param name="animate">Scroll with or without animation</param>
 934         /// <since_tizen> 8 </since_tizen>
 935         public void ScrollTo(float position, bool animate)
 936         {
 937             StopScroll();
 938             float currentPositionX = ContentContainer.CurrentPosition.X != 0 ? ContentContainer.CurrentPosition.X : ContentContainer.Position.X;
 939             float currentPositionY = ContentContainer.CurrentPosition.Y != 0 ? ContentContainer.CurrentPosition.Y : ContentContainer.Position.Y;
 940             float delta = ScrollingDirection == Direction.Horizontal ? currentPositionX : currentPositionY;
 941             // The argument position is the new pan position. So the new position of ScrollableBase becomes (-position).
 942             // To move ScrollableBase's position to (-position), it moves by (-position - currentPosition).
 943             delta = -position - delta;
 944
 945             ScrollBy(delta, animate);
 946         }
 947
 948         private float BoundScrollPosition(float targetPosition)
 949         {
 950             if (ScrollAvailableArea != null)
 951             {
 952                 float minScrollPosition = ScrollAvailableArea.X;
 953                 float maxScrollPosition = ScrollAvailableArea.Y;
 954
 955                 targetPosition = Math.Min(-minScrollPosition, targetPosition);
 956                 targetPosition = Math.Max(-maxScrollPosition, targetPosition);
 957             }
 958             else
 959             {
 960                 targetPosition = Math.Min(0, targetPosition);
 961                 targetPosition = Math.Max(-maxScrollDistance, targetPosition);
 962             }
 963
 964             return targetPosition;
 965         }
 966
 967         private void ScrollBy(float displacement, bool animate)
 968         {
 969             if (GetChildCount() == 0 || maxScrollDistance < 0)
 970             {
 971                 return;
 972             }
 973
 974             float childCurrentPosition = (ScrollingDirection == Direction.Horizontal) ? ContentContainer.PositionX : ContentContainer.PositionY;
 975
 976             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy childCurrentPosition:" + childCurrentPosition +
 977                 " displacement:" + displacement,
 978                 " maxScrollDistance:" + maxScrollDistance);
 979
 980             childTargetPosition = childCurrentPosition + displacement; // child current position + gesture displacement
 981
 982             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy currentAxisPosition:" + childCurrentPosition + "childTargetPosition:" + childTargetPosition);
 983
 984             if (animate)
 985             {
 986                 // Calculate scroll animation duration
 987                 float scrollDistance = Math.Abs(displacement);
 988                 readyToNotice = true;
 989
 990                 AnimateChildTo(ScrollDuration, BoundScrollPosition(AdjustTargetPositionOfScrollAnimation(BoundScrollPosition(childTargetPosition))));
 991             }
 992             else
 993             {
 994                 StopScroll();
 995                 finalTargetPosition = BoundScrollPosition(childTargetPosition);
 996
 997                 // Set position of scrolling child without an animation
 998                 if (ScrollingDirection == Direction.Horizontal)
 999                 {
1000                     ContentContainer.PositionX = finalTargetPosition;
1001                 }
1002                 else
1003                 {
1004                     ContentContainer.PositionY = finalTargetPosition;
1005                 }
1006             }
1007         }
1008
1009         /// <summary>
1010         /// you can override it to clean-up your own resources.
1011         /// </summary>
1012         /// <param name="type">DisposeTypes</param>
1013         /// This will be public opened in tizen_5.5 after ACR done. Before ACR, need to be hidden as inhouse API.
1014         [EditorBrowsable(EditorBrowsableState.Never)]
1015         protected override void Dispose(DisposeTypes type)
1016         {
1017             if (disposed)
1018             {
1019                 return;
1020             }
1021
1022             if (type == DisposeTypes.Explicit)
1023             {
1024                 StopOverShootingShadowAnimation();
1025                 StopScroll();
1026
1027                 if (mPanGestureDetector != null)
1028                 {
1029                     mPanGestureDetector.Detected -= OnPanGestureDetected;
1030                     mPanGestureDetector.Dispose();
1031                     mPanGestureDetector = null;
1032                 }
1033
1034                 propertyNotification.Dispose();
1035             }
1036             base.Dispose(type);
1037         }
1038
1039         private float CalculateMaximumScrollDistance()
1040         {
1041             float scrollingChildLength = 0;
1042             float scrollerLength = 0;
1043             if (ScrollingDirection == Direction.Horizontal)
1044             {
1045                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Horizontal");
1046
1047                 scrollingChildLength = ContentContainer.Size.Width;
1048                 scrollerLength = Size.Width;
1049             }
1050             else
1051             {
1052                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Vertical");
1053                 scrollingChildLength = ContentContainer.Size.Height;
1054                 scrollerLength = Size.Height;
1055             }
1056
1057             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy maxScrollDistance:" + (scrollingChildLength - scrollerLength) +
1058                 " parent length:" + scrollerLength +
1059                 " scrolling child length:" + scrollingChildLength);
1060
1061             return Math.Max(scrollingChildLength - scrollerLength, 0);
1062         }
1063
1064         private void PageSnap(float velocity)
1065         {
1066             float destination;
1067
1068             Debug.WriteLineIf(LayoutDebugScrollableBase, "PageSnap with pan candidate totalDisplacement:" + totalDisplacementForPan +
1069                 " currentPage[" + CurrentPage + "]");
1070
1071             //Increment current page if total displacement enough to warrant a page change.
1072             if (Math.Abs(totalDisplacementForPan) > (mPageWidth * ratioOfScreenWidthToCompleteScroll))
1073             {
1074                 if (totalDisplacementForPan < 0)
1075                 {
1076                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1077                 }
1078                 else
1079                 {
1080                     CurrentPage = Math.Max(0, --CurrentPage);
1081                 }
1082             }
1083             else if (Math.Abs(velocity) > PageFlickThreshold)
1084             {
1085                 if (velocity < 0)
1086                 {
1087                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1088                 }
1089                 else
1090                 {
1091                     CurrentPage = Math.Max(0, --CurrentPage);
1092                 }
1093             }
1094
1095             // Animate to new page or reposition to current page
1096             if (ScrollingDirection == Direction.Horizontal)
1097                 destination = -(Children[CurrentPage].Position.X + Children[CurrentPage].CurrentSize.Width / 2 - CurrentSize.Width / 2); // set to middle of current page
1098             else
1099                 destination = -(Children[CurrentPage].Position.Y + Children[CurrentPage].CurrentSize.Height / 2 - CurrentSize.Height / 2);
1100
1101             AnimateChildTo(ScrollDuration, destination);
1102         }
1103
1104         /// <summary>
1105         /// Enable/Disable overshooting effect. default is disabled.
1106         /// </summary>
1107         [EditorBrowsable(EditorBrowsableState.Never)]
1108         public bool EnableOverShootingEffect { get; set; } = false;
1109
1110         private void AttachOverShootingShadowView()
1111         {
1112             if (!EnableOverShootingEffect)
1113                 return;
1114
1115             // stop animation if necessary.
1116             StopOverShootingShadowAnimation();
1117
1118             if (ScrollingDirection == Direction.Horizontal)
1119             {
1120                 base.Add(leftOverShootingShadowView);
1121                 base.Add(rightOverShootingShadowView);
1122
1123                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1124                 leftOverShootingShadowView.Opacity = 1.0f;
1125                 leftOverShootingShadowView.RaiseToTop();
1126
1127                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1128                 rightOverShootingShadowView.Opacity = 1.0f;
1129                 rightOverShootingShadowView.RaiseToTop();
1130             }
1131             else
1132             {
1133                 base.Add(topOverShootingShadowView);
1134                 base.Add(bottomOverShootingShadowView);
1135
1136                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1137                 topOverShootingShadowView.Opacity = 1.0f;
1138                 topOverShootingShadowView.RaiseToTop();
1139
1140                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1141                 bottomOverShootingShadowView.Opacity = 1.0f;
1142                 bottomOverShootingShadowView.RaiseToTop();
1143             }
1144
1145             // at the beginning, height or width of overshooting shadow is 0, so it is invisible.
1146             isOverShootingShadowShown = false;
1147         }
1148
1149         private void DragOverShootingShadow(float totalPanDisplacement, float panDisplacement)
1150         {
1151             if (!EnableOverShootingEffect)
1152                 return;
1153
1154             if (totalPanDisplacement > 0) // downwards
1155             {
1156                 // check if reaching at the top / left.
1157                 if ((int)finalTargetPosition != 0)
1158                 {
1159                     isOverShootingShadowShown = false;
1160                     return;
1161                 }
1162
1163                 // save start displacement, and re-calculate displacement.
1164                 if (!isOverShootingShadowShown)
1165                 {
1166                     startShowShadowDisplacement = totalPanDisplacement;
1167                 }
1168                 isOverShootingShadowShown = true;
1169
1170                 float newDisplacement = (int)totalPanDisplacement < (int)startShowShadowDisplacement ? 0 : totalPanDisplacement - startShowShadowDisplacement;
1171
1172                 if (ScrollingDirection == Direction.Horizontal)
1173                 {
1174                     // scale limit of height is 60%.
1175                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1176                     leftOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1177
1178                     // scale limit of width is 300%.
1179                     leftOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1180
1181                     // trigger event
1182                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1183                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1184                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1185                 }
1186                 else
1187                 {
1188                     // scale limit of width is 60%.
1189                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1190                     topOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1191
1192                     // scale limit of height is 300%.
1193                     topOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1194
1195                     // trigger event
1196                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1197                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1198                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1199                 }
1200             }
1201             else if (totalPanDisplacement < 0) // upwards
1202             {
1203                 // check if reaching at the bottom.
1204                 if (-(int)finalTargetPosition != (int)maxScrollDistance)
1205                 {
1206                     isOverShootingShadowShown = false;
1207                     return;
1208                 }
1209
1210                 // save start displacement, and re-calculate displacement.
1211                 if (!isOverShootingShadowShown)
1212                 {
1213                     startShowShadowDisplacement = totalPanDisplacement;
1214                 }
1215                 isOverShootingShadowShown = true;
1216
1217                 float newDisplacement = (int)startShowShadowDisplacement < (int)totalPanDisplacement ? 0 : startShowShadowDisplacement - totalPanDisplacement;
1218
1219                 if (ScrollingDirection == Direction.Horizontal)
1220                 {
1221                     // scale limit of height is 60%.
1222                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1223                     rightOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1224
1225                     // scale limit of width is 300%.
1226                     rightOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1227
1228                     // trigger event
1229                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1230                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1231                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1232                 }
1233                 else
1234                 {
1235                     // scale limit of width is 60%.
1236                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1237                     bottomOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1238
1239                     // scale limit of height is 300%.
1240                     bottomOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1241
1242                     // trigger event
1243                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1244                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1245                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1246                 }
1247             }
1248             else
1249             {
1250                 // if total displacement is 0, shadow would become invisible.
1251                 isOverShootingShadowShown = false;
1252             }
1253         }
1254
1255         private void PlayOverShootingShadowAnimation()
1256         {
1257             if (!EnableOverShootingEffect)
1258                 return;
1259
1260             // stop animation if necessary.
1261             StopOverShootingShadowAnimation();
1262
1263             if (overShootingShadowAnimation == null)
1264             {
1265                 overShootingShadowAnimation = new Animation(overShootingShadowAnimationDuration);
1266                 overShootingShadowAnimation.Finished += OnOverShootingShadowAnimationFinished;
1267             }
1268
1269             if (ScrollingDirection == Direction.Horizontal)
1270             {
1271                 View targetView = totalDisplacementForPan < 0 ? rightOverShootingShadowView : leftOverShootingShadowView;
1272                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", SizeHeight);
1273                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", 0.0f);
1274                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1275             }
1276             else
1277             {
1278                 View targetView = totalDisplacementForPan < 0 ? bottomOverShootingShadowView : topOverShootingShadowView;
1279                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", SizeWidth);
1280                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", 0.0f);
1281                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1282             }
1283             overShootingShadowAnimation.Play();
1284         }
1285
1286         private void StopOverShootingShadowAnimation()
1287         {
1288             if (overShootingShadowAnimation == null || overShootingShadowAnimation.State != Animation.States.Playing)
1289                 return;
1290
1291             overShootingShadowAnimation.Stop(Animation.EndActions.Cancel);
1292             OnOverShootingShadowAnimationFinished(null, null);
1293             overShootingShadowAnimation.Clear();
1294         }
1295
1296         private void OnOverShootingShadowAnimationFinished(object sender, EventArgs e)
1297         {
1298             if (ScrollingDirection == Direction.Horizontal)
1299             {
1300                 base.Remove(leftOverShootingShadowView);
1301                 base.Remove(rightOverShootingShadowView);
1302
1303                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1304                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1305             }
1306             else
1307             {
1308                 base.Remove(topOverShootingShadowView);
1309                 base.Remove(bottomOverShootingShadowView);
1310
1311                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1312                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1313             }
1314
1315             // after animation finished, height/width & opacity of vertical shadow both are 0, so it is invisible.
1316             isOverShootingShadowShown = false;
1317         }
1318
1319         private void OnScrollOutOfBound(ScrollOutOfBoundEventArgs.Direction direction, float displacement)
1320         {
1321             ScrollOutOfBoundEventArgs args = new ScrollOutOfBoundEventArgs(direction, displacement);
1322             ScrollOutOfBound?.Invoke(this, args);
1323         }
1324
1325         private void OnPanGestureDetected(object source, PanGestureDetector.DetectedEventArgs e)
1326         {
1327             OnPanGesture(e.PanGesture);
1328         }
1329
1330         private void OnPanGesture(PanGesture panGesture)
1331         {
1332             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1333             {
1334                 return;
1335             }
1336
1337             if (panGesture.State == Gesture.StateType.Started)
1338             {
1339                 readyToNotice = false;
1340                 //Interrupt touching when panning is started
1341                 this.InterceptTouchEvent += OnInterruptTouchingChildTouched;
1342                 AttachOverShootingShadowView();
1343                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Gesture Start");
1344                 if (scrolling && !SnapToPage)
1345                 {
1346                     StopScroll();
1347                 }
1348                 totalDisplacementForPan = 0.0f;
1349                 OnScrollDragStarted();
1350             }
1351             else if (panGesture.State == Gesture.StateType.Continuing)
1352             {
1353                 if (ScrollingDirection == Direction.Horizontal)
1354                 {
1355                     // if vertical shadow is shown, does not scroll.
1356                     if (!isOverShootingShadowShown)
1357                     {
1358                         ScrollBy(panGesture.Displacement.X, false);
1359                     }
1360                     totalDisplacementForPan += panGesture.Displacement.X;
1361                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.X);
1362                 }
1363                 else
1364                 {
1365                     // if vertical shadow is shown, does not scroll.
1366                     if (!isOverShootingShadowShown)
1367                     {
1368                         ScrollBy(panGesture.Displacement.Y, false);
1369                     }
1370                     totalDisplacementForPan += panGesture.Displacement.Y;
1371                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.Y);
1372                 }
1373                 Debug.WriteLineIf(LayoutDebugScrollableBase, "OnPanGestureDetected Continue totalDisplacementForPan:" + totalDisplacementForPan);
1374             }
1375             else if (panGesture.State == Gesture.StateType.Finished || panGesture.State == Gesture.StateType.Cancelled)
1376             {
1377                 PlayOverShootingShadowAnimation();
1378                 OnScrollDragEnded();
1379                 StopScroll(); // Will replace previous animation so will stop existing one.
1380
1381                 if (scrollAnimation == null)
1382                 {
1383                     scrollAnimation = new Animation();
1384                     scrollAnimation.Finished += ScrollAnimationFinished;
1385                 }
1386
1387                 float panVelocity = (ScrollingDirection == Direction.Horizontal) ? panGesture.Velocity.X : panGesture.Velocity.Y;
1388
1389                 if (SnapToPage)
1390                 {
1391                     PageSnap(panVelocity);
1392                 }
1393                 else
1394                 {
1395                     if (panVelocity == 0)
1396                     {
1397                         float currentScrollPosition = (ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1398                         scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
1399                         scrollAnimation.Duration = 0;
1400                         scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", currentScrollPosition);
1401                         scrollAnimation.Play();
1402                     }
1403                     else
1404                     {
1405                         Decelerating(panVelocity, scrollAnimation);
1406                     }
1407                 }
1408
1409                 totalDisplacementForPan = 0;
1410                 scrolling = true;
1411                 readyToNotice = true;
1412                 OnScrollAnimationStarted();
1413             }
1414         }
1415
1416         internal void BaseRemove(View view)
1417         {
1418             base.Remove(view);
1419         }
1420
1421         internal override bool OnAccessibilityPan(PanGesture gestures)
1422         {
1423             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1424             {
1425                 return false;
1426             }
1427
1428             OnPanGesture(gestures);
1429             return true;
1430         }
1431
1432         private float CustomScrollAlphaFunction(float progress)
1433         {
1434             if (panAnimationDelta == 0)
1435             {
1436                 return 1.0f;
1437             }
1438             else
1439             {
1440                 // Parameter "progress" is normalized value. We need to multiply target duration to calculate distance.
1441                 // Can get real distance using equation of deceleration (check Decelerating function)
1442                 // After get real distance, normalize it
1443                 float realDuration = progress * panAnimationDuration;
1444                 float realDistance = velocityOfLastPan * ((float)Math.Pow(decelerationRate, realDuration) - 1) / logValueOfDeceleration;
1445                 float result = Math.Min(realDistance / Math.Abs(panAnimationDelta), 1.0f);
1446                 return result;
1447             }
1448         }
1449
1450         /// <summary>
1451         /// you can override it to custom your decelerating
1452         /// </summary>
1453         /// <param name="velocity">Velocity of current pan.</param>
1454         /// <param name="animation">Scroll animation.</param>
1455         [EditorBrowsable(EditorBrowsableState.Never)]
1456         protected virtual void Decelerating(float velocity, Animation animation)
1457         {
1458             // Decelerating using deceleration equation ===========
1459             //
1460             // V   : velocity (pixel per millisecond)
1461             // V0  : initial velocity
1462             // d   : deceleration rate,
1463             // t   : time
1464             // X   : final position after decelerating
1465             // log : natural logarithm
1466             //
1467             // V(t) = V0 * d pow t;
1468             // X(t) = V0 * (d pow t - 1) / log d;  <-- Integrate the velocity function
1469             // X(∞) = V0 * d / (1 - d); <-- Result using infinite T can be final position because T is tending to infinity.
1470             //
1471             // Because of final T is tending to infinity, we should use threshold value to finish.
1472             // Final T = log(-threshold * log d / |V0| ) / log d;
1473
1474             velocityOfLastPan = Math.Abs(velocity);
1475
1476             float currentScrollPosition = -(ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1477             panAnimationDelta = (velocityOfLastPan * decelerationRate) / (1 - decelerationRate);
1478             panAnimationDelta = velocity > 0 ? -panAnimationDelta : panAnimationDelta;
1479
1480             float destination = -(panAnimationDelta + currentScrollPosition);
1481             float adjustDestination = AdjustTargetPositionOfScrollAnimation(destination);
1482             float maxPosition = ScrollAvailableArea != null ? ScrollAvailableArea.Y : maxScrollDistance;
1483             float minPosition = ScrollAvailableArea != null ? ScrollAvailableArea.X : 0;
1484
1485             if (destination < -maxPosition || destination > minPosition)
1486             {
1487                 panAnimationDelta = velocity > 0 ? (currentScrollPosition - minPosition) : (maxPosition - currentScrollPosition);
1488                 destination = velocity > 0 ? minPosition : -maxPosition;
1489
1490                 if (panAnimationDelta == 0)
1491                 {
1492                     panAnimationDuration = 0.0f;
1493                 }
1494                 else
1495                 {
1496                     panAnimationDuration = (float)Math.Log((panAnimationDelta * logValueOfDeceleration / velocityOfLastPan + 1), decelerationRate);
1497                 }
1498
1499                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1500                     "OverRange======================= \n" +
1501                     "[decelerationRate] " + decelerationRate + "\n" +
1502                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1503                     "[Velocity] " + velocityOfLastPan + "\n" +
1504                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1505                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1506                     "[Destination] " + destination + "\n" +
1507                     "[Duration] " + panAnimationDuration + "\n" +
1508                     "================================ \n"
1509                 );
1510             }
1511             else
1512             {
1513                 panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1514
1515                 if (adjustDestination != destination)
1516                 {
1517                     destination = adjustDestination;
1518                     panAnimationDelta = destination + currentScrollPosition;
1519                     velocityOfLastPan = Math.Abs(panAnimationDelta * logValueOfDeceleration / ((float)Math.Pow(decelerationRate, panAnimationDuration) - 1));
1520                     panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1521                 }
1522
1523                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1524                     "================================ \n" +
1525                     "[decelerationRate] " + decelerationRate + "\n" +
1526                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1527                     "[Velocity] " + velocityOfLastPan + "\n" +
1528                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1529                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1530                     "[Destination] " + destination + "\n" +
1531                     "[Duration] " + panAnimationDuration + "\n" +
1532                     "================================ \n"
1533                 );
1534             }
1535
1536             finalTargetPosition = destination;
1537
1538             customScrollAlphaFunction = new UserAlphaFunctionDelegate(CustomScrollAlphaFunction);
1539             animation.DefaultAlphaFunction = new AlphaFunction(customScrollAlphaFunction);
1540             GC.KeepAlive(customScrollAlphaFunction);
1541             animation.Duration = (int)panAnimationDuration;
1542             animation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", destination);
1543             animation.Play();
1544         }
1545
1546         private void ScrollAnimationFinished(object sender, EventArgs e)
1547         {
1548             OnScrollAnimationEnded();
1549         }
1550
1551         /// <summary>
1552         /// Adjust scrolling position by own scrolling rules.
1553         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1554         /// </summary>
1555         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
1556         [EditorBrowsable(EditorBrowsableState.Never)]
1557         protected virtual float AdjustTargetPositionOfScrollAnimation(float position)
1558         {
1559             return position;
1560         }
1561
1562         /// <summary>
1563         /// Scroll position given to ScrollTo.
1564         /// This is the position in the opposite direction to the position of ContentContainer.
1565         /// </summary>
1566         /// <since_tizen> 8 </since_tizen>
1567         public Position ScrollPosition
1568         {
1569             get
1570             {
1571                 return new Position(-ContentContainer.Position);
1572             }
1573         }
1574
1575         /// <summary>
1576         /// Current scroll position in the middle of ScrollTo animation.
1577         /// This is the position in the opposite direction to the current position of ContentContainer.
1578         /// </summary>
1579         /// <since_tizen> 8 </since_tizen>
1580         public Position ScrollCurrentPosition
1581         {
1582             get
1583             {
1584                 return new Position(-ContentContainer.CurrentPosition);
1585             }
1586         }
1587
1588         /// <summary>
1589         /// Remove all children in ContentContainer.
1590         /// </summary>
1591         /// <param name="dispose">If true, removed child is disposed.</param>
1592         [EditorBrowsable(EditorBrowsableState.Never)]
1593         public void RemoveAllChildren(bool dispose = false)
1594         {
1595             RecursiveRemoveChildren(ContentContainer, dispose);
1596         }
1597
1598         private void RecursiveRemoveChildren(View parent, bool dispose)
1599         {
1600             if (parent == null)
1601             {
1602                 return;
1603             }
1604             int maxChild = (int)parent.GetChildCount();
1605             for (int i = maxChild - 1; i >= 0; --i)
1606             {
1607                 View child = parent.GetChildAt((uint)i);
1608                 if (child == null)
1609                 {
1610                     continue;
1611                 }
1612                 RecursiveRemoveChildren(child, dispose);
1613                 parent.Remove(child);
1614                 if (dispose)
1615                 {
1616                     child.Dispose();
1617                 }
1618             }
1619         }
1620
1621     }
1622
1623 } // namespace