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

   1 /* Copyright (c) 2020 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;
  18 using Tizen.NUI.BaseComponents;
  19 using System.Collections.Generic;
  20 using System.ComponentModel;
  21 using System.Diagnostics;
  22 using System.Runtime.InteropServices;
  23 using Tizen.NUI.Accessibility;
  24
  25 namespace Tizen.NUI.Components
  26 {
  27     /// <summary>
  28     /// ScrollEventArgs is a class to record scroll event arguments which will sent to user.
  29     /// </summary>
  30     /// <since_tizen> 8 </since_tizen>
  31     public class ScrollEventArgs : EventArgs
  32     {
  33         private Position position;
  34
  35         /// <summary>
  36         /// Default constructor.
  37         /// </summary>
  38         /// <param name="position">Current scroll position</param>
  39         /// <since_tizen> 8 </since_tizen>
  40         public ScrollEventArgs(Position position)
  41         {
  42             this.position = position;
  43         }
  44
  45         /// <summary>
  46         /// Current position of ContentContainer.
  47         /// </summary>
  48         /// <since_tizen> 8 </since_tizen>
  49         public Position Position
  50         {
  51             get
  52             {
  53                 return position;
  54             }
  55         }
  56     }
  57
  58     /// <summary>
  59     /// ScrollOutofBoundEventArgs is to record scroll out-of-bound event arguments which will be sent to user.
  60     /// </summary>
  61     [EditorBrowsable(EditorBrowsableState.Never)]
  62     public class ScrollOutOfBoundEventArgs : EventArgs
  63     {
  64         /// <summary>
  65         /// The direction to be touched.
  66         /// </summary>
  67         [EditorBrowsable(EditorBrowsableState.Never)]
  68         public enum Direction
  69         {
  70             /// <summary>
  71             /// Upwards.
  72             /// </summary>
  73             [EditorBrowsable(EditorBrowsableState.Never)]
  74             Up,
  75
  76             /// <summary>
  77             /// Downwards.
  78             /// </summary>
  79             [EditorBrowsable(EditorBrowsableState.Never)]
  80             Down,
  81
  82             /// <summary>
  83             /// Left bound.
  84             /// </summary>
  85             [EditorBrowsable(EditorBrowsableState.Never)]
  86             Left,
  87
  88             /// <summary>
  89             /// Right bound.
  90             /// </summary>
  91             [EditorBrowsable(EditorBrowsableState.Never)]
  92             Right,
  93         }
  94
  95         /// <summary>
  96         /// Constructor.
  97         /// </summary>
  98         /// <param name="direction">Current pan direction</param>
  99         /// <param name="displacement">Current total displacement</param>
 100         [EditorBrowsable(EditorBrowsableState.Never)]
 101         public ScrollOutOfBoundEventArgs(Direction direction, float displacement)
 102         {
 103             PanDirection = direction;
 104             Displacement = displacement;
 105         }
 106
 107         /// <summary>
 108         /// Current pan direction of ContentContainer.
 109         /// </summary>
 110         [EditorBrowsable(EditorBrowsableState.Never)]
 111         public Direction PanDirection
 112         {
 113             get;
 114         }
 115
 116         /// <summary>
 117         /// Current total displacement of ContentContainer.
 118         /// if its value is greater than 0, it is at the top/left;
 119         /// if less than 0, it is at the bottom/right.
 120         /// </summary>
 121         [EditorBrowsable(EditorBrowsableState.Never)]
 122         public float Displacement
 123         {
 124             get;
 125         }
 126     }
 127
 128     /// <summary>
 129     /// This class provides a View that can scroll a single View with a layout. This View can be a nest of Views.
 130     /// </summary>
 131     /// <since_tizen> 8 </since_tizen>
 132     public class ScrollableBase : Control
 133     {
 134         static bool LayoutDebugScrollableBase = false; // Debug flag
 135         private Direction mScrollingDirection = Direction.Vertical;
 136         private bool mScrollEnabled = true;
 137         private int mScrollDuration = 125;
 138         private int mPageWidth = 0;
 139         private float mPageFlickThreshold = 0.4f;
 140         private float mScrollingEventThreshold = 0.001f;
 141
 142         private class ScrollableBaseCustomLayout : AbsoluteLayout
 143         {
 144             protected override void OnMeasure(MeasureSpecification widthMeasureSpec, MeasureSpecification heightMeasureSpec)
 145             {
 146                 MeasuredSize.StateType childWidthState = MeasuredSize.StateType.MeasuredSizeOK;
 147                 MeasuredSize.StateType childHeightState = MeasuredSize.StateType.MeasuredSizeOK;
 148
 149                 Direction scrollingDirection = Direction.Vertical;
 150                 ScrollableBase scrollableBase = this.Owner as ScrollableBase;
 151                 if (scrollableBase != null)
 152                 {
 153                     scrollingDirection = scrollableBase.ScrollingDirection;
 154                 }
 155
 156                 float totalWidth = 0.0f;
 157                 float totalHeight = 0.0f;
 158
 159                 // measure child, should be a single scrolling child
 160                 foreach (LayoutItem childLayout in LayoutChildren)
 161                 {
 162                     if (childLayout != null && childLayout.Owner.Name == "ContentContainer")
 163                     {
 164                         // Get size of child
 165                         // Use an Unspecified MeasureSpecification mode so scrolling child is not restricted to it's parents size in Height (for vertical scrolling)
 166                         // or Width for horizontal scrolling
 167                         if (scrollingDirection == Direction.Vertical)
 168                         {
 169                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(heightMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 170                             MeasureChildWithMargins(childLayout, widthMeasureSpec, new LayoutLength(0), unrestrictedMeasureSpec, new LayoutLength(0)); // Height unrestricted by parent
 171                         }
 172                         else
 173                         {
 174                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(widthMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 175                             MeasureChildWithMargins(childLayout, unrestrictedMeasureSpec, new LayoutLength(0), heightMeasureSpec, new LayoutLength(0)); // Width unrestricted by parent
 176                         }
 177
 178                         totalWidth = (childLayout.MeasuredWidth.Size + (childLayout.Padding.Start + childLayout.Padding.End)).AsDecimal();
 179                         totalHeight = (childLayout.MeasuredHeight.Size + (childLayout.Padding.Top + childLayout.Padding.Bottom)).AsDecimal();
 180
 181                         if (childLayout.MeasuredWidth.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 182                         {
 183                             childWidthState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 184                         }
 185                         if (childLayout.MeasuredHeight.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 186                         {
 187                             childHeightState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 188                         }
 189                     }
 190                 }
 191
 192                 MeasuredSize widthSizeAndState = ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 193                 MeasuredSize heightSizeAndState = ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 194                 totalWidth = widthSizeAndState.Size.AsDecimal();
 195                 totalHeight = heightSizeAndState.Size.AsDecimal();
 196
 197                 // Ensure layout respects it's given minimum size
 198                 totalWidth = Math.Max(totalWidth, SuggestedMinimumWidth.AsDecimal());
 199                 totalHeight = Math.Max(totalHeight, SuggestedMinimumHeight.AsDecimal());
 200
 201                 widthSizeAndState.State = childWidthState;
 202                 heightSizeAndState.State = childHeightState;
 203
 204                 SetMeasuredDimensions(ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, childWidthState),
 205                     ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, childHeightState));
 206
 207                 // Size of ScrollableBase is changed. Change Page width too.
 208                 if (scrollableBase != null)
 209                 {
 210                     scrollableBase.mPageWidth = (int)MeasuredWidth.Size.AsRoundedValue();
 211                     scrollableBase.OnScrollingChildRelayout(null, null);
 212                 }
 213             }
 214         } //  ScrollableBaseCustomLayout
 215
 216         /// <summary>
 217         /// The direction axis to scroll.
 218         /// </summary>
 219         /// <since_tizen> 8 </since_tizen>
 220         public enum Direction
 221         {
 222             /// <summary>
 223             /// Horizontal axis.
 224             /// </summary>
 225             /// <since_tizen> 8 </since_tizen>
 226             Horizontal,
 227
 228             /// <summary>
 229             /// Vertical axis.
 230             /// </summary>
 231             /// <since_tizen> 8 </since_tizen>
 232             Vertical
 233         }
 234
 235         /// <summary>
 236         /// Scrolling direction mode.
 237         /// Default is Vertical scrolling.
 238         /// </summary>
 239         /// <since_tizen> 8 </since_tizen>
 240         public Direction ScrollingDirection
 241         {
 242             get
 243             {
 244                 return mScrollingDirection;
 245             }
 246             set
 247             {
 248                 if (value != mScrollingDirection)
 249                 {
 250                     mScrollingDirection = value;
 251                     mPanGestureDetector.ClearAngles();
 252                     mPanGestureDetector.AddDirection(value == Direction.Horizontal ?
 253                         PanGestureDetector.DirectionHorizontal : PanGestureDetector.DirectionVertical);
 254
 255                     ContentContainer.WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent;
 256                     ContentContainer.HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent;
 257                 }
 258             }
 259         }
 260
 261         /// <summary>
 262         /// Enable or disable scrolling.
 263         /// </summary>
 264         /// <since_tizen> 8 </since_tizen>
 265         public bool ScrollEnabled
 266         {
 267             get
 268             {
 269                 return mScrollEnabled;
 270             }
 271             set
 272             {
 273                 if (value != mScrollEnabled)
 274                 {
 275                     mScrollEnabled = value;
 276                     if (mScrollEnabled)
 277                     {
 278                         mPanGestureDetector.Detected += OnPanGestureDetected;
 279                     }
 280                     else
 281                     {
 282                         mPanGestureDetector.Detected -= OnPanGestureDetected;
 283                     }
 284                 }
 285             }
 286         }
 287
 288         /// <summary>
 289         /// Pages mode, enables moving to the next or return to current page depending on pan displacement.
 290         /// Default is false.
 291         /// </summary>
 292         /// <since_tizen> 8 </since_tizen>
 293         public bool SnapToPage { set; get; } = false;
 294
 295         /// <summary>
 296         /// Get current page.
 297         /// Working property with SnapToPage property.
 298         /// </summary>
 299         /// <since_tizen> 8 </since_tizen>
 300         public int CurrentPage { get; private set; } = 0;
 301
 302         /// <summary>
 303         /// Duration of scroll animation.
 304         /// Default value is 125ms.
 305         /// </summary>
 306         /// <since_tizen> 8 </since_tizen>
 307         public int ScrollDuration
 308         {
 309             set
 310             {
 311                 mScrollDuration = value >= 0 ? value : mScrollDuration;
 312             }
 313             get
 314             {
 315                 return mScrollDuration;
 316             }
 317         }
 318
 319         /// <summary>
 320         /// Scroll Available area.
 321         /// </summary>
 322         /// <since_tizen> 8 </since_tizen>
 323         public Vector2 ScrollAvailableArea { set; get; }
 324
 325         /// <summary>
 326         /// An event emitted when user starts dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 327         /// </summary>
 328         /// <since_tizen> 8 </since_tizen>
 329         public event EventHandler<ScrollEventArgs> ScrollDragStarted;
 330
 331         /// <summary>
 332         /// An event emitted when user stops dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 333         /// </summary>
 334         /// <since_tizen> 8 </since_tizen>
 335         public event EventHandler<ScrollEventArgs> ScrollDragEnded;
 336
 337         /// <summary>
 338         /// An event emitted when the scrolling slide animation starts, user can subscribe or unsubscribe to this event handler.<br />
 339         /// </summary>
 340         /// <since_tizen> 8 </since_tizen>
 341         public event EventHandler<ScrollEventArgs> ScrollAnimationStarted;
 342
 343         /// <summary>
 344         /// An event emitted when the scrolling slide animation ends, user can subscribe or unsubscribe to this event handler.<br />
 345         /// </summary>
 346         /// <since_tizen> 8 </since_tizen>
 347         public event EventHandler<ScrollEventArgs> ScrollAnimationEnded;
 348
 349         /// <summary>
 350         /// An event emitted when scrolling, user can subscribe or unsubscribe to this event handler.<br />
 351         /// </summary>
 352         /// <since_tizen> 8 </since_tizen>
 353         public event EventHandler<ScrollEventArgs> Scrolling;
 354
 355         /// <summary>
 356         /// An event emitted when scrolling out of bound, user can subscribe or unsubscribe to this event handler.<br />
 357         /// </summary>
 358         [EditorBrowsable(EditorBrowsableState.Never)]
 359         public event EventHandler<ScrollOutOfBoundEventArgs> ScrollOutOfBound;
 360
 361         /// <summary>
 362         /// Scrollbar for ScrollableBase.
 363         /// </summary>
 364         /// <since_tizen> 8 </since_tizen>
 365         public ScrollbarBase Scrollbar
 366         {
 367             get
 368             {
 369                 return scrollBar;
 370             }
 371             set
 372             {
 373                 if (scrollBar)
 374                 {
 375                     base.Remove(scrollBar);
 376                 }
 377                 scrollBar = value;
 378
 379                 if (scrollBar != null)
 380                 {
 381                     scrollBar.Name = "ScrollBar";
 382                     base.Add(scrollBar);
 383
 384                     if (hideScrollbar)
 385                     {
 386                         scrollBar.Hide();
 387                     }
 388                     else
 389                     {
 390                         scrollBar.Show();
 391                     }
 392
 393                     SetScrollbar();
 394                 }
 395             }
 396         }
 397
 398         /// <summary>
 399         /// Always hide Scrollbar.
 400         /// </summary>
 401         /// <since_tizen> 8 </since_tizen>
 402         public bool HideScrollbar
 403         {
 404             get
 405             {
 406                 return hideScrollbar;
 407             }
 408             set
 409             {
 410                 hideScrollbar = value;
 411
 412                 if (scrollBar)
 413                 {
 414                     if (value)
 415                     {
 416                         scrollBar.Hide();
 417                     }
 418                     else
 419                     {
 420                         scrollBar.Show();
 421                     }
 422                 }
 423             }
 424         }
 425
 426         /// <summary>
 427         /// Container which has content of ScrollableBase.
 428         /// </summary>
 429         /// <since_tizen> 8 </since_tizen>
 430         public View ContentContainer { get; private set; }
 431
 432         /// <summary>
 433         /// Set the layout on this View. Replaces any existing Layout.
 434         /// </summary>
 435         /// <since_tizen> 8 </since_tizen>
 436         public new LayoutItem Layout
 437         {
 438             get
 439             {
 440                 return ContentContainer.Layout;
 441             }
 442             set
 443             {
 444                 ContentContainer.Layout = value;
 445             }
 446         }
 447
 448         /// <summary>
 449         /// List of children of Container.
 450         /// </summary>
 451         /// <since_tizen> 8 </since_tizen>
 452         public new List<View> Children
 453         {
 454             get
 455             {
 456                 return ContentContainer.Children;
 457             }
 458         }
 459
 460         /// <summary>
 461         /// Deceleration rate of scrolling by finger.
 462         /// Rate should be bigger than 0 and smaller than 1.
 463         /// Default value is 0.998f;
 464         /// </summary>
 465         /// <since_tizen> 8 </since_tizen>
 466         public float DecelerationRate
 467         {
 468             get
 469             {
 470                 return decelerationRate;
 471             }
 472             set
 473             {
 474                 decelerationRate = (value < 1 && value > 0) ? value : decelerationRate;
 475                 logValueOfDeceleration = (float)Math.Log(value);
 476             }
 477         }
 478
 479         /// <summary>
 480         /// Threashold not to go infinit at the end of scrolling animation.
 481         /// </summary>
 482         [EditorBrowsable(EditorBrowsableState.Never)]
 483         public float DecelerationThreshold { get; set; } = 0.1f;
 484
 485         /// <summary>
 486         /// Scrolling event will be thrown when this amount of scroll position is changed.
 487         /// If this threshold becomes smaller, the tracking detail increases but the scrolling range that can be tracked becomes smaller.
 488         /// If large sized ContentContainer is required, please use larger threshold value.
 489         /// Default ScrollingEventThreshold value is 0.001f.
 490         /// </summary>
 491         [EditorBrowsable(EditorBrowsableState.Never)]
 492         public float ScrollingEventThreshold
 493         {
 494             get
 495             {
 496                 return mScrollingEventThreshold;
 497             }
 498             set
 499             {
 500                 if (mScrollingEventThreshold != value && value > 0)
 501                 {
 502                     ContentContainer.RemovePropertyNotification(propertyNotification);
 503                     propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(value));
 504                     propertyNotification.Notified += OnPropertyChanged;
 505                     mScrollingEventThreshold = value;
 506                 }
 507             }
 508         }
 509
 510         /// <summary>
 511         /// Page will be changed when velocity of panning is over threshold.
 512         /// The unit of threshold is pixel per milisec.
 513         /// </summary>
 514         /// <since_tizen> 8 </since_tizen>
 515         public float PageFlickThreshold
 516         {
 517             get
 518             {
 519                 return mPageFlickThreshold;
 520             }
 521             set
 522             {
 523                 mPageFlickThreshold = value >= 0f ? value : mPageFlickThreshold;
 524             }
 525         }
 526
 527         /// <summary>
 528         /// Padding for the ScrollableBase
 529         /// </summary>
 530         [EditorBrowsable(EditorBrowsableState.Never)]
 531         public Extents Padding
 532         {
 533             get
 534             {
 535                 return ContentContainer.Padding;
 536             }
 537             set
 538             {
 539                 ContentContainer.Padding = value;
 540             }
 541         }
 542
 543         /// <summary>
 544         /// Alphafunction for scroll animation.
 545         /// </summary>
 546         [EditorBrowsable(EditorBrowsableState.Never)]
 547         public AlphaFunction ScrollAlphaFunction { get; set; } = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
 548
 549         private bool hideScrollbar = true;
 550         private float maxScrollDistance;
 551         private float childTargetPosition = 0.0f;
 552         private PanGestureDetector mPanGestureDetector;
 553         private View mInterruptTouchingChild;
 554         private ScrollbarBase scrollBar;
 555         private bool scrolling = false;
 556         private float ratioOfScreenWidthToCompleteScroll = 0.5f;
 557         private float totalDisplacementForPan = 0.0f;
 558         private Size previousContainerSize = new Size();
 559         private Size previousSize = new Size();
 560         private PropertyNotification propertyNotification;
 561         private float noticeAnimationEndBeforePosition = 0.0f;
 562         private bool readyToNotice = false;
 563
 564         /// <summary>
 565         /// Notice before animation is finished.
 566         /// </summary>
 567         [EditorBrowsable(EditorBrowsableState.Never)]
 568         // Let's consider more whether this needs to be set as protected.
 569         public float NoticeAnimationEndBeforePosition
 570         {
 571             get => noticeAnimationEndBeforePosition;
 572             set => noticeAnimationEndBeforePosition = value;
 573         }
 574
 575         // Let's consider more whether this needs to be set as protected.
 576         private float finalTargetPosition;
 577
 578         private Animation scrollAnimation;
 579         // Declare user alpha function delegate
 580         [UnmanagedFunctionPointer(CallingConvention.StdCall)]
 581         private delegate float UserAlphaFunctionDelegate(float progress);
 582         private UserAlphaFunctionDelegate customScrollAlphaFunction;
 583         private float velocityOfLastPan = 0.0f;
 584         private float panAnimationDuration = 0.0f;
 585         private float panAnimationDelta = 0.0f;
 586         private float logValueOfDeceleration = 0.0f;
 587         private float decelerationRate = 0.0f;
 588
 589         private View topOverShootingShadowView;
 590         private View bottomOverShootingShadowView;
 591         private View leftOverShootingShadowView;
 592         private View rightOverShootingShadowView;
 593         private const int overShootingShadowScaleHeightLimit = 64 * 3;
 594         private const int overShootingShadowAnimationDuration = 300;
 595         private Animation overShootingShadowAnimation;
 596         private bool isOverShootingShadowShown = false;
 597         private float startShowShadowDisplacement;
 598
 599         /// <summary>
 600         /// Default Constructor
 601         /// </summary>
 602         /// <since_tizen> 8 </since_tizen>
 603         public ScrollableBase() : base()
 604         {
 605             DecelerationRate = 0.998f;
 606
 607             base.Layout = new ScrollableBaseCustomLayout();
 608             mPanGestureDetector = new PanGestureDetector();
 609             mPanGestureDetector.Attach(this);
 610             mPanGestureDetector.AddDirection(PanGestureDetector.DirectionVertical);
 611             mPanGestureDetector.Detected += OnPanGestureDetected;
 612
 613             ClippingMode = ClippingModeType.ClipToBoundingBox;
 614
 615             //Default Scrolling child
 616             ContentContainer = new View()
 617             {
 618                 Name = "ContentContainer",
 619                 WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent,
 620                 HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent,
 621             };
 622             ContentContainer.Relayout += OnScrollingChildRelayout;
 623             propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(mScrollingEventThreshold));
 624             propertyNotification.Notified += OnPropertyChanged;
 625             base.Add(ContentContainer);
 626
 627             //Interrupt touching when panning is started
 628             mInterruptTouchingChild = new View()
 629             {
 630                 Size = new Size(Window.Instance.WindowSize),
 631                 BackgroundColor = Color.Transparent,
 632             };
 633             mInterruptTouchingChild.TouchEvent += OnIterruptTouchingChildTouched;
 634             Scrollbar = new Scrollbar();
 635
 636             //Show vertical shadow on the top (or bottom) of the scrollable when panning down (or up).
 637             topOverShootingShadowView = new View
 638             {
 639                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_top.png",
 640                 Opacity = 1.0f,
 641                 SizeHeight = 0.0f,
 642                 PositionUsesPivotPoint = true,
 643                 ParentOrigin = NUI.ParentOrigin.TopCenter,
 644                 PivotPoint = NUI.PivotPoint.TopCenter,
 645             };
 646             bottomOverShootingShadowView = new View
 647             {
 648                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_bottom.png",
 649                 Opacity = 1.0f,
 650                 SizeHeight = 0.0f,
 651                 PositionUsesPivotPoint = true,
 652                 ParentOrigin = NUI.ParentOrigin.BottomCenter,
 653                 PivotPoint = NUI.PivotPoint.BottomCenter,
 654             };
 655             //Show horizontal shadow on the left (or right) of the scrollable when panning down (or up).
 656             leftOverShootingShadowView = new View
 657             {
 658                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_left.png",
 659                 Opacity = 1.0f,
 660                 SizeWidth = 0.0f,
 661                 PositionUsesPivotPoint = true,
 662                 ParentOrigin = NUI.ParentOrigin.CenterLeft,
 663                 PivotPoint = NUI.PivotPoint.CenterLeft,
 664             };
 665             rightOverShootingShadowView = new View
 666             {
 667                 BackgroundImage = FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_right.png",
 668                 Opacity = 1.0f,
 669                 SizeWidth = 0.0f,
 670                 PositionUsesPivotPoint = true,
 671                 ParentOrigin = NUI.ParentOrigin.CenterRight,
 672                 PivotPoint = NUI.PivotPoint.CenterRight,
 673             };
 674
 675             AccessibilityManager.Instance.SetAccessibilityAttribute(this, AccessibilityManager.AccessibilityAttribute.Trait, "ScrollableBase");
 676         }
 677
 678         private bool OnIterruptTouchingChildTouched(object source, View.TouchEventArgs args)
 679         {
 680             if (args.Touch.GetState(0) == PointStateType.Down)
 681             {
 682                 if (scrolling && !SnapToPage)
 683                 {
 684                     StopScroll();
 685                 }
 686             }
 687             return true;
 688         }
 689
 690         private void OnPropertyChanged(object source, PropertyNotification.NotifyEventArgs args)
 691         {
 692             OnScroll();
 693         }
 694
 695         /// <summary>
 696         /// Called after a child has been added to the owning view.
 697         /// </summary>
 698         /// <param name="view">The child which has been added.</param>
 699         /// <since_tizen> 8 </since_tizen>
 700         public override void Add(View view)
 701         {
 702             ContentContainer.Add(view);
 703         }
 704
 705         /// <summary>
 706         /// Called after a child has been removed from the owning view.
 707         /// </summary>
 708         /// <param name="view">The child which has been removed.</param>
 709         /// <since_tizen> 8 </since_tizen>
 710         public override void Remove(View view)
 711         {
 712             if (SnapToPage && CurrentPage == Children.IndexOf(view) && CurrentPage == Children.Count - 1)
 713             {
 714                 // Target View is current page and also last child.
 715                 // CurrentPage should be changed to previous page.
 716                 CurrentPage = Math.Max(0, CurrentPage - 1);
 717                 ScrollToIndex(CurrentPage);
 718             }
 719
 720             ContentContainer.Remove(view);
 721         }
 722
 723         private void OnScrollingChildRelayout(object source, EventArgs args)
 724         {
 725             // Size is changed. Calculate maxScrollDistance.
 726             bool isSizeChanged = previousContainerSize.Width != ContentContainer.Size.Width || previousContainerSize.Height != ContentContainer.Size.Height ||
 727                 previousSize.Width != Size.Width || previousSize.Height != Size.Height;
 728
 729             if (isSizeChanged)
 730             {
 731                 maxScrollDistance = CalculateMaximumScrollDistance();
 732                 SetScrollbar();
 733             }
 734
 735             previousContainerSize = ContentContainer.Size;
 736             previousSize = Size;
 737         }
 738
 739         /// <summary>
 740         /// The composition of a Scrollbar can vary depending on how you use ScrollableBase.
 741         /// Set the composition that will go into the ScrollableBase according to your ScrollableBase.
 742         /// </summary>
 743         /// <since_tizen> 8 </since_tizen>
 744         [EditorBrowsable(EditorBrowsableState.Never)]
 745         protected virtual void SetScrollbar()
 746         {
 747             if (Scrollbar)
 748             {
 749                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 750                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 751                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 752                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 753                 Scrollbar.Initialize(contentLength, viewportLength, currentPosition, isHorizontal);
 754             }
 755         }
 756
 757         /// <summary>
 758         /// Scrolls to the item at the specified index.
 759         /// </summary>
 760         /// <param name="index">Index of item.</param>
 761         /// <since_tizen> 8 </since_tizen>
 762         public void ScrollToIndex(int index)
 763         {
 764             if (ContentContainer.ChildCount - 1 < index || index < 0)
 765             {
 766                 return;
 767             }
 768
 769             if (SnapToPage)
 770             {
 771                 CurrentPage = index;
 772             }
 773
 774             float targetPosition = Math.Min(ScrollingDirection == Direction.Vertical ? Children[index].Position.Y : Children[index].Position.X, maxScrollDistance);
 775             AnimateChildTo(ScrollDuration, -targetPosition);
 776         }
 777
 778         private void OnScrollDragStarted()
 779         {
 780             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 781             ScrollDragStarted?.Invoke(this, eventArgs);
 782         }
 783
 784         private void OnScrollDragEnded()
 785         {
 786             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 787             ScrollDragEnded?.Invoke(this, eventArgs);
 788         }
 789
 790         private void OnScrollAnimationStarted()
 791         {
 792             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 793             ScrollAnimationStarted?.Invoke(this, eventArgs);
 794         }
 795
 796         private void OnScrollAnimationEnded()
 797         {
 798             scrolling = false;
 799             base.Remove(mInterruptTouchingChild);
 800
 801             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 802             ScrollAnimationEnded?.Invoke(this, eventArgs);
 803         }
 804
 805         private void OnScroll()
 806         {
 807             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 808             Scrolling?.Invoke(this, eventArgs);
 809
 810             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 811             float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 812             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 813
 814             scrollBar?.Update(contentLength, Math.Abs(currentPosition));
 815             CheckPreReachedTargetPosition();
 816         }
 817
 818         private void CheckPreReachedTargetPosition()
 819         {
 820             // Check whether we reached pre-reached target position
 821             if (readyToNotice &&
 822                 ContentContainer.CurrentPosition.Y <= finalTargetPosition + NoticeAnimationEndBeforePosition &&
 823                 ContentContainer.CurrentPosition.Y >= finalTargetPosition - NoticeAnimationEndBeforePosition)
 824             {
 825                 //Notice first
 826                 readyToNotice = false;
 827                 OnPreReachedTargetPosition(finalTargetPosition);
 828             }
 829         }
 830
 831         /// <summary>
 832         /// This helps developer who wants to know before scroll is reaching target position.
 833         /// </summary>
 834         /// <param name="targetPosition">Index of item.</param>
 835         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
 836         [EditorBrowsable(EditorBrowsableState.Never)]
 837         protected virtual void OnPreReachedTargetPosition(float targetPosition)
 838         {
 839
 840         }
 841
 842         private void StopScroll()
 843         {
 844             if (scrollAnimation != null)
 845             {
 846                 if (scrollAnimation.State == Animation.States.Playing)
 847                 {
 848                     Debug.WriteLineIf(LayoutDebugScrollableBase, "StopScroll Animation Playing");
 849                     scrollAnimation.Stop(Animation.EndActions.Cancel);
 850                     OnScrollAnimationEnded();
 851                 }
 852                 scrollAnimation.Clear();
 853             }
 854         }
 855
 856         private void AnimateChildTo(int duration, float axisPosition)
 857         {
 858             Debug.WriteLineIf(LayoutDebugScrollableBase, "AnimationTo Animation Duration:" + duration + " Destination:" + axisPosition);
 859             finalTargetPosition = axisPosition;
 860
 861             StopScroll(); // Will replace previous animation so will stop existing one.
 862
 863             if (scrollAnimation == null)
 864             {
 865                 scrollAnimation = new Animation();
 866                 scrollAnimation.Finished += ScrollAnimationFinished;
 867             }
 868
 869             scrollAnimation.Duration = duration;
 870             scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.EaseOutSquare);
 871             scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", axisPosition, ScrollAlphaFunction);
 872             scrolling = true;
 873             OnScrollAnimationStarted();
 874             scrollAnimation.Play();
 875         }
 876
 877         /// <summary>
 878         /// Scroll to specific position with or without animation.
 879         /// </summary>
 880         /// <param name="position">Destination.</param>
 881         /// <param name="animate">Scroll with or without animation</param>
 882         /// <since_tizen> 8 </since_tizen>
 883         public void ScrollTo(float position, bool animate)
 884         {
 885             float currentPositionX = ContentContainer.CurrentPosition.X != 0 ? ContentContainer.CurrentPosition.X : ContentContainer.Position.X;
 886             float currentPositionY = ContentContainer.CurrentPosition.Y != 0 ? ContentContainer.CurrentPosition.Y : ContentContainer.Position.Y;
 887             float delta = ScrollingDirection == Direction.Horizontal ? currentPositionX : currentPositionY;
 888             // The argument position is the new pan position. So the new position of ScrollableBase becomes (-position).
 889             // To move ScrollableBase's position to (-position), it moves by (-position - currentPosition).
 890             delta = -position - delta;
 891
 892             ScrollBy(delta, animate);
 893         }
 894
 895         private float BoundScrollPosition(float targetPosition)
 896         {
 897             if (ScrollAvailableArea != null)
 898             {
 899                 float minScrollPosition = ScrollAvailableArea.X;
 900                 float maxScrollPosition = ScrollAvailableArea.Y;
 901
 902                 targetPosition = Math.Min(-minScrollPosition, targetPosition);
 903                 targetPosition = Math.Max(-maxScrollPosition, targetPosition);
 904             }
 905             else
 906             {
 907                 targetPosition = Math.Min(0, targetPosition);
 908                 targetPosition = Math.Max(-maxScrollDistance, targetPosition);
 909             }
 910
 911             return targetPosition;
 912         }
 913
 914         private void ScrollBy(float displacement, bool animate)
 915         {
 916             if (GetChildCount() == 0 || maxScrollDistance < 0)
 917             {
 918                 return;
 919             }
 920
 921             float childCurrentPosition = (ScrollingDirection == Direction.Horizontal) ? ContentContainer.PositionX : ContentContainer.PositionY;
 922
 923             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy childCurrentPosition:" + childCurrentPosition +
 924                 " displacement:" + displacement,
 925                 " maxScrollDistance:" + maxScrollDistance);
 926
 927             childTargetPosition = childCurrentPosition + displacement; // child current position + gesture displacement
 928
 929             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy currentAxisPosition:" + childCurrentPosition + "childTargetPosition:" + childTargetPosition);
 930
 931             if (animate)
 932             {
 933                 // Calculate scroll animaton duration
 934                 float scrollDistance = Math.Abs(displacement);
 935                 readyToNotice = true;
 936
 937                 AnimateChildTo(ScrollDuration, BoundScrollPosition(AdjustTargetPositionOfScrollAnimation(BoundScrollPosition(childTargetPosition))));
 938             }
 939             else
 940             {
 941                 finalTargetPosition = BoundScrollPosition(childTargetPosition);
 942
 943                 // Set position of scrolling child without an animation
 944                 if (ScrollingDirection == Direction.Horizontal)
 945                 {
 946                     ContentContainer.PositionX = finalTargetPosition;
 947                 }
 948                 else
 949                 {
 950                     ContentContainer.PositionY = finalTargetPosition;
 951                 }
 952             }
 953         }
 954
 955         /// <summary>
 956         /// you can override it to clean-up your own resources.
 957         /// </summary>
 958         /// <param name="type">DisposeTypes</param>
 959         /// This will be public opened in tizen_5.5 after ACR done. Before ACR, need to be hidden as inhouse API.
 960         [EditorBrowsable(EditorBrowsableState.Never)]
 961         protected override void Dispose(DisposeTypes type)
 962         {
 963             if (disposed)
 964             {
 965                 return;
 966             }
 967
 968             if (type == DisposeTypes.Explicit)
 969             {
 970                 StopOverShootingShadowAnimation();
 971                 StopScroll();
 972
 973                 if (mPanGestureDetector != null)
 974                 {
 975                     mPanGestureDetector.Detected -= OnPanGestureDetected;
 976                     mPanGestureDetector.Dispose();
 977                     mPanGestureDetector = null;
 978                 }
 979
 980                 propertyNotification.Dispose();
 981             }
 982             base.Dispose(type);
 983         }
 984
 985         private float CalculateMaximumScrollDistance()
 986         {
 987             float scrollingChildLength = 0;
 988             float scrollerLength = 0;
 989             if (ScrollingDirection == Direction.Horizontal)
 990             {
 991                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Horizontal");
 992
 993                 scrollingChildLength = ContentContainer.Size.Width;
 994                 scrollerLength = Size.Width;
 995             }
 996             else
 997             {
 998                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Vertical");
 999                 scrollingChildLength = ContentContainer.Size.Height;
1000                 scrollerLength = Size.Height;
1001             }
1002
1003             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy maxScrollDistance:" + (scrollingChildLength - scrollerLength) +
1004                 " parent length:" + scrollerLength +
1005                 " scrolling child length:" + scrollingChildLength);
1006
1007             return Math.Max(scrollingChildLength - scrollerLength, 0);
1008         }
1009
1010         private void PageSnap(float velocity)
1011         {
1012             Debug.WriteLineIf(LayoutDebugScrollableBase, "PageSnap with pan candidate totalDisplacement:" + totalDisplacementForPan +
1013                 " currentPage[" + CurrentPage + "]");
1014
1015             //Increment current page if total displacement enough to warrant a page change.
1016             if (Math.Abs(totalDisplacementForPan) > (mPageWidth * ratioOfScreenWidthToCompleteScroll))
1017             {
1018                 if (totalDisplacementForPan < 0)
1019                 {
1020                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1021                 }
1022                 else
1023                 {
1024                     CurrentPage = Math.Max(0, --CurrentPage);
1025                 }
1026             }
1027             else if (Math.Abs(velocity) > PageFlickThreshold)
1028             {
1029                 if (velocity < 0)
1030                 {
1031                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1032                 }
1033                 else
1034                 {
1035                     CurrentPage = Math.Max(0, --CurrentPage);
1036                 }
1037             }
1038
1039             // Animate to new page or reposition to current page
1040             float destinationX = -(Children[CurrentPage].Position.X + Children[CurrentPage].CurrentSize.Width / 2 - CurrentSize.Width / 2); // set to middle of current page
1041             Debug.WriteLineIf(LayoutDebugScrollableBase, "Snapping to page[" + CurrentPage + "] to:" + destinationX + " from:" + ContentContainer.PositionX);
1042             AnimateChildTo(ScrollDuration, destinationX);
1043         }
1044
1045         /// <summary>
1046         /// Enable/Disable overshooting effect. default is disabled.
1047         /// </summary>
1048         [EditorBrowsable(EditorBrowsableState.Never)]
1049         public bool EnableOverShootingEffect { get; set; } = false;
1050
1051         private void AttachOverShootingShadowView()
1052         {
1053             if (!EnableOverShootingEffect)
1054                 return;
1055
1056             // stop animation if necessary.
1057             StopOverShootingShadowAnimation();
1058
1059             if (ScrollingDirection == Direction.Horizontal)
1060             {
1061                 base.Add(leftOverShootingShadowView);
1062                 base.Add(rightOverShootingShadowView);
1063
1064                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1065                 leftOverShootingShadowView.Opacity = 1.0f;
1066                 leftOverShootingShadowView.RaiseToTop();
1067
1068                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1069                 rightOverShootingShadowView.Opacity = 1.0f;
1070                 rightOverShootingShadowView.RaiseToTop();
1071             }
1072             else
1073             {
1074                 base.Add(topOverShootingShadowView);
1075                 base.Add(bottomOverShootingShadowView);
1076
1077                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1078                 topOverShootingShadowView.Opacity = 1.0f;
1079                 topOverShootingShadowView.RaiseToTop();
1080
1081                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1082                 bottomOverShootingShadowView.Opacity = 1.0f;
1083                 bottomOverShootingShadowView.RaiseToTop();
1084             }
1085
1086             // at the beginning, height or width of overshooting shadow is 0, so it is invisible.
1087             isOverShootingShadowShown = false;
1088         }
1089
1090         private void DragOverShootingShadow(float totalPanDisplacement, float panDisplacement)
1091         {
1092             if (!EnableOverShootingEffect)
1093                 return;
1094
1095             if (totalPanDisplacement > 0) // downwards
1096             {
1097                 // check if reaching at the top / left.
1098                 if ((int)finalTargetPosition != 0)
1099                 {
1100                     isOverShootingShadowShown = false;
1101                     return;
1102                 }
1103
1104                 // save start displacement, and re-calculate displacement.
1105                 if (!isOverShootingShadowShown)
1106                 {
1107                     startShowShadowDisplacement = totalPanDisplacement;
1108                 }
1109                 isOverShootingShadowShown = true;
1110
1111                 float newDisplacement = (int)totalPanDisplacement < (int)startShowShadowDisplacement ? 0 : totalPanDisplacement - startShowShadowDisplacement;
1112
1113                 if (ScrollingDirection == Direction.Horizontal)
1114                 {
1115                     // scale limit of height is 60%.
1116                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1117                     leftOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1118
1119                     // scale limit of width is 300%.
1120                     leftOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1121
1122                     // trigger event
1123                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1124                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1125                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1126                 }
1127                 else
1128                 {
1129                     // scale limit of width is 60%.
1130                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1131                     topOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1132
1133                     // scale limit of height is 300%.
1134                     topOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1135
1136                     // trigger event
1137                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1138                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1139                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1140                 }
1141             }
1142             else if (totalPanDisplacement < 0) // upwards
1143             {
1144                 // check if reaching at the bottom.
1145                 if (-(int)finalTargetPosition != (int)maxScrollDistance)
1146                 {
1147                     isOverShootingShadowShown = false;
1148                     return;
1149                 }
1150
1151                 // save start displacement, and re-calculate displacement.
1152                 if (!isOverShootingShadowShown)
1153                 {
1154                     startShowShadowDisplacement = totalPanDisplacement;
1155                 }
1156                 isOverShootingShadowShown = true;
1157
1158                 float newDisplacement = (int)startShowShadowDisplacement < (int)totalPanDisplacement ? 0 : startShowShadowDisplacement - totalPanDisplacement;
1159
1160                 if (ScrollingDirection == Direction.Horizontal)
1161                 {
1162                     // scale limit of height is 60%.
1163                     float heightScale = newDisplacement / overShootingShadowScaleHeightLimit;
1164                     rightOverShootingShadowView.SizeHeight = heightScale > 0.6f ? SizeHeight * 0.4f : SizeHeight * (1.0f - heightScale);
1165
1166                     // scale limit of width is 300%.
1167                     rightOverShootingShadowView.SizeWidth = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1168
1169                     // trigger event
1170                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1171                        ScrollOutOfBoundEventArgs.Direction.Right : ScrollOutOfBoundEventArgs.Direction.Left;
1172                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1173                 }
1174                 else
1175                 {
1176                     // scale limit of width is 60%.
1177                     float widthScale = newDisplacement / overShootingShadowScaleHeightLimit;
1178                     bottomOverShootingShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1179
1180                     // scale limit of height is 300%.
1181                     bottomOverShootingShadowView.SizeHeight = newDisplacement > overShootingShadowScaleHeightLimit ? overShootingShadowScaleHeightLimit : newDisplacement;
1182
1183                     // trigger event
1184                     ScrollOutOfBoundEventArgs.Direction scrollDirection = panDisplacement > 0 ?
1185                        ScrollOutOfBoundEventArgs.Direction.Down : ScrollOutOfBoundEventArgs.Direction.Up;
1186                     OnScrollOutOfBound(scrollDirection, totalPanDisplacement);
1187                 }
1188             }
1189             else
1190             {
1191                 // if total displacement is 0, shadow would become invisible.
1192                 isOverShootingShadowShown = false;
1193             }
1194         }
1195
1196         private void PlayOverShootingShadowAnimation()
1197         {
1198             if (!EnableOverShootingEffect)
1199                 return;
1200
1201             // stop animation if necessary.
1202             StopOverShootingShadowAnimation();
1203
1204             if (overShootingShadowAnimation == null)
1205             {
1206                 overShootingShadowAnimation = new Animation(overShootingShadowAnimationDuration);
1207                 overShootingShadowAnimation.Finished += OnOverShootingShadowAnimationFinished;
1208             }
1209
1210             if (ScrollingDirection == Direction.Horizontal)
1211             {
1212                 View targetView = totalDisplacementForPan < 0 ? rightOverShootingShadowView : leftOverShootingShadowView;
1213                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", SizeHeight);
1214                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", 0.0f);
1215                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1216             }
1217             else
1218             {
1219                 View targetView = totalDisplacementForPan < 0 ? bottomOverShootingShadowView : topOverShootingShadowView;
1220                 overShootingShadowAnimation.AnimateTo(targetView, "SizeWidth", SizeWidth);
1221                 overShootingShadowAnimation.AnimateTo(targetView, "SizeHeight", 0.0f);
1222                 overShootingShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1223             }
1224             overShootingShadowAnimation.Play();
1225         }
1226
1227         private void StopOverShootingShadowAnimation()
1228         {
1229             if (overShootingShadowAnimation == null || overShootingShadowAnimation.State != Animation.States.Playing)
1230                 return;
1231
1232             overShootingShadowAnimation.Stop(Animation.EndActions.Cancel);
1233             OnOverShootingShadowAnimationFinished(null, null);
1234             overShootingShadowAnimation.Clear();
1235         }
1236
1237         private void OnOverShootingShadowAnimationFinished(object sender, EventArgs e)
1238         {
1239             if (ScrollingDirection == Direction.Horizontal)
1240             {
1241                 base.Remove(leftOverShootingShadowView);
1242                 base.Remove(rightOverShootingShadowView);
1243
1244                 leftOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1245                 rightOverShootingShadowView.Size = new Size(0.0f, SizeHeight);
1246             }
1247             else
1248             {
1249                 base.Remove(topOverShootingShadowView);
1250                 base.Remove(bottomOverShootingShadowView);
1251
1252                 topOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1253                 bottomOverShootingShadowView.Size = new Size(SizeWidth, 0.0f);
1254             }
1255
1256             // after animation finished, height/width & opacity of vertical shadow both are 0, so it is invisible.
1257             isOverShootingShadowShown = false;
1258         }
1259
1260         private void OnScrollOutOfBound(ScrollOutOfBoundEventArgs.Direction direction, float displacement)
1261         {
1262             ScrollOutOfBoundEventArgs args = new ScrollOutOfBoundEventArgs(direction, displacement);
1263             ScrollOutOfBound?.Invoke(this, args);
1264         }
1265
1266         private void OnPanGestureDetected(object source, PanGestureDetector.DetectedEventArgs e)
1267         {
1268             OnPanGesture(e.PanGesture);
1269         }
1270
1271         private void OnPanGesture(PanGesture panGesture)
1272         {
1273             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1274             {
1275                 return;
1276             }
1277
1278             if (panGesture.State == Gesture.StateType.Started)
1279             {
1280                 readyToNotice = false;
1281                 base.Add(mInterruptTouchingChild);
1282                 AttachOverShootingShadowView();
1283                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Gesture Start");
1284                 if (scrolling && !SnapToPage)
1285                 {
1286                     StopScroll();
1287                 }
1288                 totalDisplacementForPan = 0.0f;
1289                 OnScrollDragStarted();
1290             }
1291             else if (panGesture.State == Gesture.StateType.Continuing)
1292             {
1293                 if (ScrollingDirection == Direction.Horizontal)
1294                 {
1295                     // if vertical shadow is shown, does not scroll.
1296                     if (!isOverShootingShadowShown)
1297                     {
1298                         ScrollBy(panGesture.Displacement.X, false);
1299                     }
1300                     totalDisplacementForPan += panGesture.Displacement.X;
1301                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.X);
1302                 }
1303                 else
1304                 {
1305                     // if vertical shadow is shown, does not scroll.
1306                     if (!isOverShootingShadowShown)
1307                     {
1308                         ScrollBy(panGesture.Displacement.Y, false);
1309                     }
1310                     totalDisplacementForPan += panGesture.Displacement.Y;
1311                     DragOverShootingShadow(totalDisplacementForPan, panGesture.Displacement.Y);
1312                 }
1313                 Debug.WriteLineIf(LayoutDebugScrollableBase, "OnPanGestureDetected Continue totalDisplacementForPan:" + totalDisplacementForPan);
1314             }
1315             else if (panGesture.State == Gesture.StateType.Finished || panGesture.State == Gesture.StateType.Cancelled)
1316             {
1317                 PlayOverShootingShadowAnimation();
1318                 OnScrollDragEnded();
1319                 StopScroll(); // Will replace previous animation so will stop existing one.
1320
1321                 if (scrollAnimation == null)
1322                 {
1323                     scrollAnimation = new Animation();
1324                     scrollAnimation.Finished += ScrollAnimationFinished;
1325                 }
1326
1327                 float panVelocity = (ScrollingDirection == Direction.Horizontal) ? panGesture.Velocity.X : panGesture.Velocity.Y;
1328
1329                 if (SnapToPage)
1330                 {
1331                     PageSnap(panVelocity);
1332                 }
1333                 else
1334                 {
1335                     if (panVelocity == 0)
1336                     {
1337                         float currentScrollPosition = (ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1338                         scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
1339                         scrollAnimation.Duration = 0;
1340                         scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", currentScrollPosition);
1341                         scrollAnimation.Play();
1342                     }
1343                     else
1344                     {
1345                         Decelerating(panVelocity, scrollAnimation);
1346                     }
1347                 }
1348
1349                 totalDisplacementForPan = 0;
1350                 scrolling = true;
1351                 readyToNotice = true;
1352                 OnScrollAnimationStarted();
1353             }
1354         }
1355
1356         internal void BaseRemove(View view)
1357         {
1358             base.Remove(view);
1359         }
1360
1361         internal override bool OnAccessibilityPan(PanGesture gestures)
1362         {
1363             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1364             {
1365                 return false;
1366             }
1367
1368             OnPanGesture(gestures);
1369             return true;
1370         }
1371
1372         private float CustomScrollAlphaFunction(float progress)
1373         {
1374             if (panAnimationDelta == 0)
1375             {
1376                 return 1.0f;
1377             }
1378             else
1379             {
1380                 // Parameter "progress" is normalized value. We need to multiply target duration to calculate distance.
1381                 // Can get real distance using equation of deceleration (check Decelerating function)
1382                 // After get real distance, normalize it
1383                 float realDuration = progress * panAnimationDuration;
1384                 float realDistance = velocityOfLastPan * ((float)Math.Pow(decelerationRate, realDuration) - 1) / logValueOfDeceleration;
1385                 float result = Math.Min(realDistance / Math.Abs(panAnimationDelta), 1.0f);
1386                 return result;
1387             }
1388         }
1389
1390         /// <summary>
1391         /// you can override it to custom your decelerating
1392         /// </summary>
1393         /// <param name="velocity">Velocity of current pan.</param>
1394         /// <param name="animation">Scroll animation.</param>
1395         [EditorBrowsable(EditorBrowsableState.Never)]
1396         protected virtual void Decelerating(float velocity, Animation animation)
1397         {
1398             // Decelerating using deceleration equation ===========
1399             //
1400             // V   : velocity (pixel per milisecond)
1401             // V0  : initial velocity
1402             // d   : deceleration rate,
1403             // t   : time
1404             // X   : final position after decelerating
1405             // log : natural logarithm
1406             //
1407             // V(t) = V0 * d pow t;
1408             // X(t) = V0 * (d pow t - 1) / log d;  <-- Integrate the velocity function
1409             // X(∞) = V0 * d / (1 - d); <-- Result using inifit T can be final position because T is tending to infinity.
1410             //
1411             // Because of final T is tending to inifity, we should use threshold value to finish.
1412             // Final T = log(-threshold * log d / |V0| ) / log d;
1413
1414             velocityOfLastPan = Math.Abs(velocity);
1415
1416             float currentScrollPosition = -(ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1417             panAnimationDelta = (velocityOfLastPan * decelerationRate) / (1 - decelerationRate);
1418             panAnimationDelta = velocity > 0 ? -panAnimationDelta : panAnimationDelta;
1419
1420             float destination = -(panAnimationDelta + currentScrollPosition);
1421             float adjustDestination = AdjustTargetPositionOfScrollAnimation(destination);
1422             float maxPosition = ScrollAvailableArea != null ? ScrollAvailableArea.Y : maxScrollDistance;
1423             float minPosition = ScrollAvailableArea != null ? ScrollAvailableArea.X : 0;
1424
1425             if (destination < -maxPosition || destination > minPosition)
1426             {
1427                 panAnimationDelta = velocity > 0 ? (currentScrollPosition - minPosition) : (maxPosition - currentScrollPosition);
1428                 destination = velocity > 0 ? minPosition : -maxPosition;
1429
1430                 if (panAnimationDelta == 0)
1431                 {
1432                     panAnimationDuration = 0.0f;
1433                 }
1434                 else
1435                 {
1436                     panAnimationDuration = (float)Math.Log((panAnimationDelta * logValueOfDeceleration / velocityOfLastPan + 1), decelerationRate);
1437                 }
1438
1439                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1440                     "OverRange======================= \n" +
1441                     "[decelerationRate] " + decelerationRate + "\n" +
1442                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1443                     "[Velocity] " + velocityOfLastPan + "\n" +
1444                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1445                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1446                     "[Destination] " + destination + "\n" +
1447                     "[Duration] " + panAnimationDuration + "\n" +
1448                     "================================ \n"
1449                 );
1450             }
1451             else
1452             {
1453                 panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1454
1455                 if (adjustDestination != destination)
1456                 {
1457                     destination = adjustDestination;
1458                     panAnimationDelta = destination + currentScrollPosition;
1459                     velocityOfLastPan = Math.Abs(panAnimationDelta * logValueOfDeceleration / ((float)Math.Pow(decelerationRate, panAnimationDuration) - 1));
1460                     panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1461                 }
1462
1463                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1464                     "================================ \n" +
1465                     "[decelerationRate] " + decelerationRate + "\n" +
1466                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1467                     "[Velocity] " + velocityOfLastPan + "\n" +
1468                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1469                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1470                     "[Destination] " + destination + "\n" +
1471                     "[Duration] " + panAnimationDuration + "\n" +
1472                     "================================ \n"
1473                 );
1474             }
1475
1476             finalTargetPosition = destination;
1477
1478             customScrollAlphaFunction = new UserAlphaFunctionDelegate(CustomScrollAlphaFunction);
1479             animation.DefaultAlphaFunction = new AlphaFunction(customScrollAlphaFunction);
1480             GC.KeepAlive(customScrollAlphaFunction);
1481             animation.Duration = (int)panAnimationDuration;
1482             animation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", destination);
1483             animation.Play();
1484         }
1485
1486         private void ScrollAnimationFinished(object sender, EventArgs e)
1487         {
1488             OnScrollAnimationEnded();
1489         }
1490
1491         /// <summary>
1492         /// Adjust scrolling position by own scrolling rules.
1493         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1494         /// </summary>
1495         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
1496         [EditorBrowsable(EditorBrowsableState.Never)]
1497         protected virtual float AdjustTargetPositionOfScrollAnimation(float position)
1498         {
1499             return position;
1500         }
1501
1502         /// <summary>
1503         /// Scroll position given to ScrollTo.
1504         /// This is the position in the opposite direction to the position of ContentContainer.
1505         /// </summary>
1506         /// <since_tizen> 8 </since_tizen>
1507         public Position ScrollPosition
1508         {
1509             get
1510             {
1511                 return new Position(-ContentContainer.Position);
1512             }
1513         }
1514
1515         /// <summary>
1516         /// Current scroll position in the middle of ScrollTo animation.
1517         /// This is the position in the opposite direction to the current position of ContentContainer.
1518         /// </summary>
1519         /// <since_tizen> 8 </since_tizen>
1520         public Position ScrollCurrentPosition
1521         {
1522             get
1523             {
1524                 return new Position(-ContentContainer.CurrentPosition);
1525             }
1526         }
1527
1528         /// <summary>
1529         /// Remove all children in ContentContainer.
1530         /// </summary>
1531         /// <param name="dispose">If true, removed child is disposed.</param>
1532         [EditorBrowsable(EditorBrowsableState.Never)]
1533         public void RemoveAllChildren(bool dispose = false)
1534         {
1535             RecursiveRemoveChildren(ContentContainer, dispose);
1536         }
1537
1538         private void RecursiveRemoveChildren(View parent, bool dispose)
1539         {
1540             if (parent == null)
1541             {
1542                 return;
1543             }
1544             int maxChild = (int)parent.GetChildCount();
1545             for (int i = maxChild - 1; i >= 0; --i)
1546             {
1547                 View child = parent.GetChildAt((uint)i);
1548                 if (child == null)
1549                 {
1550                     continue;
1551                 }
1552                 RecursiveRemoveChildren(child, dispose);
1553                 parent.Remove(child);
1554                 if (dispose)
1555                 {
1556                     child.Dispose();
1557                 }
1558             }
1559         }
1560
1561     }
1562
1563 } // namespace