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