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 bound to be scrolled out of.
  66         /// </summary>
  67         [EditorBrowsable(EditorBrowsableState.Never)]
  68         public enum Bound
  69         {
  70             /// <summary>
  71             /// Top bound.
  72             /// </summary>
  73             [EditorBrowsable(EditorBrowsableState.Never)]
  74             Top,
  75
  76             /// <summary>
  77             /// Bottom bound.
  78             /// </summary>
  79             [EditorBrowsable(EditorBrowsableState.Never)]
  80             Bottom
  81         }
  82
  83         /// <summary>
  84         /// Default constructor.
  85         /// </summary>
  86         /// <param name="bound">Current scrollable bound</param>
  87         [EditorBrowsable(EditorBrowsableState.Never)]
  88         public ScrollOutOfBoundEventArgs(Bound bound)
  89         {
  90             ScrollableBound = bound;
  91         }
  92
  93         /// <summary>
  94         /// Current position of ContentContainer.
  95         /// </summary>
  96         [EditorBrowsable(EditorBrowsableState.Never)]
  97         public Bound ScrollableBound
  98         {
  99             get;
 100         }
 101     }
 102
 103     /// <summary>
 104     /// ScrollOutOfBoundWithDisplacementEventArgs is to record scroll out-of-bound event arguments which will be sent to user.
 105     /// </summary>
 106     [EditorBrowsable(EditorBrowsableState.Never)]
 107     public class ScrollOutOfBoundWithDisplacementEventArgs : EventArgs
 108     {
 109         /// <summary>
 110         /// The direction to be touched.
 111         /// </summary>
 112         [EditorBrowsable(EditorBrowsableState.Never)]
 113         public enum Direction
 114         {
 115             /// <summary>
 116             /// Upwards.
 117             /// </summary>
 118             [EditorBrowsable(EditorBrowsableState.Never)]
 119             Up,
 120
 121             /// <summary>
 122             /// Downwards.
 123             /// </summary>
 124             [EditorBrowsable(EditorBrowsableState.Never)]
 125             Down,
 126         }
 127
 128         /// <summary>
 129         /// Constructor.
 130         /// </summary>
 131         /// <param name="direction">Current pan direction</param>
 132         /// <param name="displacement">Current total displacement</param>
 133         [EditorBrowsable(EditorBrowsableState.Never)]
 134         public ScrollOutOfBoundWithDisplacementEventArgs(Direction direction, float displacement)
 135         {
 136             PanDirection = direction;
 137             Displacement = displacement;
 138         }
 139
 140         /// <summary>
 141         /// Current pan direction of ContentContainer.
 142         /// </summary>
 143         [EditorBrowsable(EditorBrowsableState.Never)]
 144         public Direction PanDirection
 145         {
 146             get;
 147         }
 148
 149         /// <summary>
 150         /// Current total displacement of ContentContainer.
 151         /// if its value is greater than 0, it is at the top/left;
 152         /// if less than 0, it is at the bottom/right.
 153         /// </summary>
 154         [EditorBrowsable(EditorBrowsableState.Never)]
 155         public float Displacement
 156         {
 157             get;
 158         }
 159     }
 160
 161     /// <summary>
 162     /// This class provides a View that can scroll a single View with a layout. This View can be a nest of Views.
 163     /// </summary>
 164     /// <since_tizen> 8 </since_tizen>
 165     public class ScrollableBase : Control
 166     {
 167         static bool LayoutDebugScrollableBase = false; // Debug flag
 168         private Direction mScrollingDirection = Direction.Vertical;
 169         private bool mScrollEnabled = true;
 170         private int mScrollDuration = 125;
 171         private int mPageWidth = 0;
 172         private float mPageFlickThreshold = 0.4f;
 173         private float mScrollingEventThreshold = 0.00001f;
 174
 175         private class ScrollableBaseCustomLayout : LayoutGroup
 176         {
 177             protected override void OnMeasure(MeasureSpecification widthMeasureSpec, MeasureSpecification heightMeasureSpec)
 178             {
 179                 MeasuredSize.StateType childWidthState = MeasuredSize.StateType.MeasuredSizeOK;
 180                 MeasuredSize.StateType childHeightState = MeasuredSize.StateType.MeasuredSizeOK;
 181
 182                 Direction scrollingDirection = Direction.Vertical;
 183                 ScrollableBase scrollableBase = this.Owner as ScrollableBase;
 184                 if (scrollableBase != null)
 185                 {
 186                     scrollingDirection = scrollableBase.ScrollingDirection;
 187                 }
 188
 189                 float totalWidth = 0.0f;
 190                 float totalHeight = 0.0f;
 191
 192                 // measure child, should be a single scrolling child
 193                 foreach (LayoutItem childLayout in LayoutChildren)
 194                 {
 195                     if (childLayout != null && childLayout.Owner.Name == "ContentContainer")
 196                     {
 197                         // Get size of child
 198                         // Use an Unspecified MeasureSpecification mode so scrolling child is not restricted to it's parents size in Height (for vertical scrolling)
 199                         // or Width for horizontal scrolling
 200                         if (scrollingDirection == Direction.Vertical)
 201                         {
 202                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(heightMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 203                             MeasureChildWithMargins(childLayout, widthMeasureSpec, new LayoutLength(0), unrestrictedMeasureSpec, new LayoutLength(0)); // Height unrestricted by parent
 204                         }
 205                         else
 206                         {
 207                             MeasureSpecification unrestrictedMeasureSpec = new MeasureSpecification(widthMeasureSpec.Size, MeasureSpecification.ModeType.Unspecified);
 208                             MeasureChildWithMargins(childLayout, unrestrictedMeasureSpec, new LayoutLength(0), heightMeasureSpec, new LayoutLength(0)); // Width unrestricted by parent
 209                         }
 210
 211                         totalWidth = (childLayout.MeasuredWidth.Size + (childLayout.Padding.Start + childLayout.Padding.End)).AsDecimal();
 212                         totalHeight = (childLayout.MeasuredHeight.Size + (childLayout.Padding.Top + childLayout.Padding.Bottom)).AsDecimal();
 213
 214                         if (childLayout.MeasuredWidth.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 215                         {
 216                             childWidthState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 217                         }
 218                         if (childLayout.MeasuredHeight.State == MeasuredSize.StateType.MeasuredSizeTooSmall)
 219                         {
 220                             childHeightState = MeasuredSize.StateType.MeasuredSizeTooSmall;
 221                         }
 222                     }
 223                 }
 224
 225                 MeasuredSize widthSizeAndState = ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 226                 MeasuredSize heightSizeAndState = ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, MeasuredSize.StateType.MeasuredSizeOK);
 227                 totalWidth = widthSizeAndState.Size.AsDecimal();
 228                 totalHeight = heightSizeAndState.Size.AsDecimal();
 229
 230                 // Ensure layout respects it's given minimum size
 231                 totalWidth = Math.Max(totalWidth, SuggestedMinimumWidth.AsDecimal());
 232                 totalHeight = Math.Max(totalHeight, SuggestedMinimumHeight.AsDecimal());
 233
 234                 widthSizeAndState.State = childWidthState;
 235                 heightSizeAndState.State = childHeightState;
 236
 237                 SetMeasuredDimensions(ResolveSizeAndState(new LayoutLength(totalWidth), widthMeasureSpec, childWidthState),
 238                     ResolveSizeAndState(new LayoutLength(totalHeight), heightMeasureSpec, childHeightState));
 239
 240                 // Size of ScrollableBase is changed. Change Page width too.
 241                 if (scrollableBase != null)
 242                 {
 243                     scrollableBase.mPageWidth = (int)MeasuredWidth.Size.AsRoundedValue();
 244                     scrollableBase.OnScrollingChildRelayout(null, null);
 245                 }
 246             }
 247
 248             protected override void OnLayout(bool changed, LayoutLength left, LayoutLength top, LayoutLength right, LayoutLength bottom)
 249             {
 250                 foreach (LayoutItem childLayout in LayoutChildren)
 251                 {
 252                     if (childLayout != null && childLayout.Owner.Name == "ContentContainer")
 253                     {
 254                         LayoutLength childWidth = childLayout.MeasuredWidth.Size;
 255                         LayoutLength childHeight = childLayout.MeasuredHeight.Size;
 256
 257                         Position2D childPosition = childLayout.Owner.Position2D;
 258
 259                         LayoutLength childLeft = new LayoutLength(childPosition.X);
 260                         LayoutLength childTop = new LayoutLength(childPosition.Y);
 261
 262                         childLayout.Layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);
 263                     }
 264                 }
 265             }
 266         } //  ScrollableBaseCustomLayout
 267
 268         /// <summary>
 269         /// The direction axis to scroll.
 270         /// </summary>
 271         /// <since_tizen> 8 </since_tizen>
 272         public enum Direction
 273         {
 274             /// <summary>
 275             /// Horizontal axis.
 276             /// </summary>
 277             /// <since_tizen> 8 </since_tizen>
 278             Horizontal,
 279
 280             /// <summary>
 281             /// Vertical axis.
 282             /// </summary>
 283             /// <since_tizen> 8 </since_tizen>
 284             Vertical
 285         }
 286
 287         /// <summary>
 288         /// Scrolling direction mode.
 289         /// Default is Vertical scrolling.
 290         /// </summary>
 291         /// <since_tizen> 8 </since_tizen>
 292         public Direction ScrollingDirection
 293         {
 294             get
 295             {
 296                 return mScrollingDirection;
 297             }
 298             set
 299             {
 300                 if (value != mScrollingDirection)
 301                 {
 302                     mScrollingDirection = value;
 303                     mPanGestureDetector.ClearAngles();
 304                     mPanGestureDetector.AddDirection(value == Direction.Horizontal ?
 305                         PanGestureDetector.DirectionHorizontal : PanGestureDetector.DirectionVertical);
 306
 307                     ContentContainer.WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent;
 308                     ContentContainer.HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent;
 309                 }
 310             }
 311         }
 312
 313         /// <summary>
 314         /// Enable or disable scrolling.
 315         /// </summary>
 316         /// <since_tizen> 8 </since_tizen>
 317         public bool ScrollEnabled
 318         {
 319             get
 320             {
 321                 return mScrollEnabled;
 322             }
 323             set
 324             {
 325                 if (value != mScrollEnabled)
 326                 {
 327                     mScrollEnabled = value;
 328                     if (mScrollEnabled)
 329                     {
 330                         mPanGestureDetector.Detected += OnPanGestureDetected;
 331                     }
 332                     else
 333                     {
 334                         mPanGestureDetector.Detected -= OnPanGestureDetected;
 335                     }
 336                 }
 337             }
 338         }
 339
 340         /// <summary>
 341         /// Pages mode, enables moving to the next or return to current page depending on pan displacement.
 342         /// Default is false.
 343         /// </summary>
 344         /// <since_tizen> 8 </since_tizen>
 345         public bool SnapToPage { set; get; } = false;
 346
 347         /// <summary>
 348         /// Get current page.
 349         /// Working property with SnapToPage property.
 350         /// </summary>
 351         /// <since_tizen> 8 </since_tizen>
 352         public int CurrentPage { get; private set; } = 0;
 353
 354         /// <summary>
 355         /// Duration of scroll animation.
 356         /// Default value is 125ms.
 357         /// </summary>
 358         /// <since_tizen> 8 </since_tizen>
 359         public int ScrollDuration
 360         {
 361             set
 362             {
 363                 mScrollDuration = value >= 0 ? value : mScrollDuration;
 364             }
 365             get
 366             {
 367                 return mScrollDuration;
 368             }
 369         }
 370
 371         /// <summary>
 372         /// Scroll Available area.
 373         /// </summary>
 374         /// <since_tizen> 8 </since_tizen>
 375         public Vector2 ScrollAvailableArea { set; get; }
 376
 377         /// <summary>
 378         /// An event emitted when user starts dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 379         /// </summary>
 380         /// <since_tizen> 8 </since_tizen>
 381         public event EventHandler<ScrollEventArgs> ScrollDragStarted;
 382
 383         /// <summary>
 384         /// An event emitted when user stops dragging ScrollableBase, user can subscribe or unsubscribe to this event handler.<br />
 385         /// </summary>
 386         /// <since_tizen> 8 </since_tizen>
 387         public event EventHandler<ScrollEventArgs> ScrollDragEnded;
 388
 389         /// <summary>
 390         /// An event emitted when the scrolling slide animation starts, user can subscribe or unsubscribe to this event handler.<br />
 391         /// </summary>
 392         /// <since_tizen> 8 </since_tizen>
 393         public event EventHandler<ScrollEventArgs> ScrollAnimationStarted;
 394
 395         /// <summary>
 396         /// An event emitted when the scrolling slide animation ends, user can subscribe or unsubscribe to this event handler.<br />
 397         /// </summary>
 398         /// <since_tizen> 8 </since_tizen>
 399         public event EventHandler<ScrollEventArgs> ScrollAnimationEnded;
 400
 401         /// <summary>
 402         /// An event emitted when scrolling, user can subscribe or unsubscribe to this event handler.<br />
 403         /// </summary>
 404         /// <since_tizen> 8 </since_tizen>
 405         public event EventHandler<ScrollEventArgs> Scrolling;
 406
 407         /// <summary>
 408         /// An event emitted when scrolling out of bound, user can subscribe or unsubscribe to this event handler.<br />
 409         /// </summary>
 410         [EditorBrowsable(EditorBrowsableState.Never)]
 411         public event EventHandler<ScrollOutOfBoundEventArgs> ScrollOutOfBound;
 412
 413         /// <summary>
 414         /// An event emitted when scrolling out of bound, user can subscribe or unsubscribe to this event handler.<br />
 415         /// </summary>
 416         [EditorBrowsable(EditorBrowsableState.Never)]
 417         public event EventHandler<ScrollOutOfBoundWithDisplacementEventArgs> ScrollOutOfBoundWithDisplacement;
 418
 419         /// <summary>
 420         /// Scrollbar for ScrollableBase.
 421         /// </summary>
 422         /// <since_tizen> 8 </since_tizen>
 423         public ScrollbarBase Scrollbar
 424         {
 425             get
 426             {
 427                 return scrollBar;
 428             }
 429             set
 430             {
 431                 if (scrollBar)
 432                 {
 433                     base.Remove(scrollBar);
 434                 }
 435                 scrollBar = value;
 436
 437                 if (scrollBar != null)
 438                 {
 439                     scrollBar.Name = "ScrollBar";
 440                     base.Add(scrollBar);
 441
 442                     if (hideScrollbar)
 443                     {
 444                         scrollBar.Hide();
 445                     }
 446                     else
 447                     {
 448                         scrollBar.Show();
 449                     }
 450
 451                     SetScrollbar();
 452                 }
 453             }
 454         }
 455
 456         /// <summary>
 457         /// Always hide Scrollbar.
 458         /// </summary>
 459         /// <since_tizen> 8 </since_tizen>
 460         public bool HideScrollbar
 461         {
 462             get
 463             {
 464                 return hideScrollbar;
 465             }
 466             set
 467             {
 468                 hideScrollbar = value;
 469
 470                 if (scrollBar)
 471                 {
 472                     if (value)
 473                     {
 474                         scrollBar.Hide();
 475                     }
 476                     else
 477                     {
 478                         scrollBar.Show();
 479                     }
 480                 }
 481             }
 482         }
 483
 484         /// <summary>
 485         /// Container which has content of ScrollableBase.
 486         /// </summary>
 487         /// <since_tizen> 8 </since_tizen>
 488         public View ContentContainer { get; private set; }
 489
 490         /// <summary>
 491         /// Set the layout on this View. Replaces any existing Layout.
 492         /// </summary>
 493         /// <since_tizen> 8 </since_tizen>
 494         public new LayoutItem Layout
 495         {
 496             get
 497             {
 498                 return ContentContainer.Layout;
 499             }
 500             set
 501             {
 502                 ContentContainer.Layout = value;
 503                 if (ContentContainer.Layout != null)
 504                 {
 505                     ContentContainer.Layout.SetPositionByLayout = false;
 506                 }
 507             }
 508         }
 509
 510         /// <summary>
 511         /// List of children of Container.
 512         /// </summary>
 513         /// <since_tizen> 8 </since_tizen>
 514         public new List<View> Children
 515         {
 516             get
 517             {
 518                 return ContentContainer.Children;
 519             }
 520         }
 521
 522         /// <summary>
 523         /// Deceleration rate of scrolling by finger.
 524         /// Rate should be bigger than 0 and smaller than 1.
 525         /// Default value is 0.998f;
 526         /// </summary>
 527         /// <since_tizen> 8 </since_tizen>
 528         public float DecelerationRate
 529         {
 530             get
 531             {
 532                 return decelerationRate;
 533             }
 534             set
 535             {
 536                 decelerationRate = (value < 1 && value > 0) ? value : decelerationRate;
 537                 logValueOfDeceleration = (float)Math.Log(value);
 538             }
 539         }
 540
 541         /// <summary>
 542         /// Threashold not to go infinit at the end of scrolling animation.
 543         /// </summary>
 544         [EditorBrowsable(EditorBrowsableState.Never)]
 545         public float DecelerationThreshold { get; set; } = 0.1f;
 546
 547         /// <summary>
 548         /// Scrolling event will be thrown when this amount of scroll positino is changed.
 549         /// </summary>
 550         [EditorBrowsable(EditorBrowsableState.Never)]
 551         public float ScrollingEventThreshold
 552         {
 553             get
 554             {
 555                 return mScrollingEventThreshold;
 556             }
 557             set
 558             {
 559                 if (mScrollingEventThreshold != value && value > 0)
 560                 {
 561                     ContentContainer.RemovePropertyNotification(propertyNotification);
 562                     propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(value));
 563                     propertyNotification.Notified += OnPropertyChanged;
 564                     mScrollingEventThreshold = value;
 565                 }
 566             }
 567         }
 568
 569         /// <summary>
 570         /// Page will be changed when velocity of panning is over threshold.
 571         /// The unit of threshold is pixel per milisec.
 572         /// </summary>
 573         /// <since_tizen> 8 </since_tizen>
 574         public float PageFlickThreshold
 575         {
 576             get
 577             {
 578                 return mPageFlickThreshold;
 579             }
 580             set
 581             {
 582                 mPageFlickThreshold = value >= 0f ? value : mPageFlickThreshold;
 583             }
 584         }
 585
 586         /// <summary>
 587         /// Padding for the ScrollableBase
 588         /// </summary>
 589         [EditorBrowsable(EditorBrowsableState.Never)]
 590         public Extents Padding
 591         {
 592             get
 593             {
 594                 return ContentContainer.Padding;
 595             }
 596             set
 597             {
 598                 ContentContainer.Padding = value;
 599             }
 600         }
 601
 602         /// <summary>
 603         /// Alphafunction for scroll animation.
 604         /// </summary>
 605         [EditorBrowsable(EditorBrowsableState.Never)]
 606         public AlphaFunction ScrollAlphaFunction { get; set; } = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
 607
 608         private bool hideScrollbar = true;
 609         private float maxScrollDistance;
 610         private float childTargetPosition = 0.0f;
 611         private PanGestureDetector mPanGestureDetector;
 612         private View mInterruptTouchingChild;
 613         private ScrollbarBase scrollBar;
 614         private bool scrolling = false;
 615         private float ratioOfScreenWidthToCompleteScroll = 0.5f;
 616         private float totalDisplacementForPan = 0.0f;
 617         private Size previousContainerSize = new Size();
 618         private Size previousSize = new Size();
 619         private PropertyNotification propertyNotification;
 620         private float noticeAnimationEndBeforePosition = 0.0f;
 621         private bool readyToNotice = false;
 622
 623         /// <summary>
 624         /// Notice before animation is finished.
 625         /// </summary>
 626         [EditorBrowsable(EditorBrowsableState.Never)]
 627         // Let's consider more whether this needs to be set as protected.
 628         public float NoticeAnimationEndBeforePosition
 629         {
 630             get => noticeAnimationEndBeforePosition;
 631             set => noticeAnimationEndBeforePosition = value;
 632         }
 633
 634         // Let's consider more whether this needs to be set as protected.
 635         private float finalTargetPosition;
 636
 637         private Animation scrollAnimation;
 638         // Declare user alpha function delegate
 639         [UnmanagedFunctionPointer(CallingConvention.StdCall)]
 640         private delegate float UserAlphaFunctionDelegate(float progress);
 641         private UserAlphaFunctionDelegate customScrollAlphaFunction;
 642         private float velocityOfLastPan = 0.0f;
 643         private float panAnimationDuration = 0.0f;
 644         private float panAnimationDelta = 0.0f;
 645         private float logValueOfDeceleration = 0.0f;
 646         private float decelerationRate = 0.0f;
 647
 648         private View verticalTopShadowView;
 649         private View verticalBottomShadowView;
 650         private const int verticalShadowScaleHeightLimit = 64 * 3;
 651         private const int verticalShadowAnimationDuration = 300;
 652         private Animation verticalShadowAnimation;
 653         private bool isVerticalShadowShown = false;
 654         private float startShowShadowDisplacement;
 655
 656         /// <summary>
 657         /// Default Constructor
 658         /// </summary>
 659         /// <since_tizen> 8 </since_tizen>
 660         public ScrollableBase() : base()
 661         {
 662             DecelerationRate = 0.998f;
 663
 664             base.Layout = new ScrollableBaseCustomLayout();
 665             mPanGestureDetector = new PanGestureDetector();
 666             mPanGestureDetector.Attach(this);
 667             mPanGestureDetector.AddDirection(PanGestureDetector.DirectionVertical);
 668             mPanGestureDetector.Detected += OnPanGestureDetected;
 669
 670             ClippingMode = ClippingModeType.ClipToBoundingBox;
 671
 672             //Default Scrolling child
 673             ContentContainer = new View()
 674             {
 675                 Name = "ContentContainer",
 676                 WidthSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.MatchParent : LayoutParamPolicies.WrapContent,
 677                 HeightSpecification = ScrollingDirection == Direction.Vertical ? LayoutParamPolicies.WrapContent : LayoutParamPolicies.MatchParent,
 678                 Layout = new AbsoluteLayout()
 679                 {
 680                     SetPositionByLayout = false
 681                 },
 682             };
 683             ContentContainer.Relayout += OnScrollingChildRelayout;
 684             propertyNotification = ContentContainer.AddPropertyNotification("position", PropertyCondition.Step(mScrollingEventThreshold));
 685             propertyNotification.Notified += OnPropertyChanged;
 686             base.Add(ContentContainer);
 687
 688             //Interrupt touching when panning is started
 689             mInterruptTouchingChild = new View()
 690             {
 691                 Size = new Size(Window.Instance.WindowSize),
 692                 BackgroundColor = Color.Transparent,
 693             };
 694             mInterruptTouchingChild.TouchEvent += OnIterruptTouchingChildTouched;
 695             Scrollbar = new Scrollbar();
 696
 697             //Show vertical shadow on the top (or bottom) of the scrollable when panning down (or up).
 698             verticalTopShadowView = new View
 699             {
 700                 BackgroundImage = Tizen.NUI.FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_top.png",
 701                 Opacity = 1.0f,
 702                 SizeHeight = 0.0f,
 703                 PositionUsesPivotPoint = true,
 704                 ParentOrigin = NUI.ParentOrigin.TopCenter,
 705                 PivotPoint = NUI.PivotPoint.TopCenter,
 706             };
 707             verticalBottomShadowView = new View
 708             {
 709                 BackgroundImage = Tizen.NUI.FrameworkInformation.ResourcePath + "nui_component_default_scroll_over_shooting_bottom.png",
 710                 Opacity = 1.0f,
 711                 SizeHeight = 0.0f,
 712                 PositionUsesPivotPoint = true,
 713                 ParentOrigin = NUI.ParentOrigin.BottomCenter,
 714                 PivotPoint = NUI.PivotPoint.BottomCenter,
 715             };
 716 #if (PROFILE_MOBILE)
 717             AccessibilityManager.Instance.SetAccessibilityAttribute(this, AccessibilityManager.AccessibilityAttribute.Trait, "ScrollableBase");
 718 #endif
 719         }
 720
 721         private bool OnIterruptTouchingChildTouched(object source, View.TouchEventArgs args)
 722         {
 723             if (args.Touch.GetState(0) == PointStateType.Down)
 724             {
 725                 if (scrolling && !SnapToPage)
 726                 {
 727                     StopScroll();
 728                 }
 729             }
 730             return true;
 731         }
 732
 733         private void OnPropertyChanged(object source, PropertyNotification.NotifyEventArgs args)
 734         {
 735             OnScroll();
 736         }
 737
 738         /// <summary>
 739         /// Called after a child has been added to the owning view.
 740         /// </summary>
 741         /// <param name="view">The child which has been added.</param>
 742         /// <since_tizen> 8 </since_tizen>
 743         public override void Add(View view)
 744         {
 745             ContentContainer.Add(view);
 746         }
 747
 748         /// <summary>
 749         /// Called after a child has been removed from the owning view.
 750         /// </summary>
 751         /// <param name="view">The child which has been removed.</param>
 752         /// <since_tizen> 8 </since_tizen>
 753         public override void Remove(View view)
 754         {
 755             if (SnapToPage && CurrentPage == Children.IndexOf(view) && CurrentPage == Children.Count - 1)
 756             {
 757                 // Target View is current page and also last child.
 758                 // CurrentPage should be changed to previous page.
 759                 CurrentPage = Math.Max(0, CurrentPage - 1);
 760                 ScrollToIndex(CurrentPage);
 761             }
 762
 763             ContentContainer.Remove(view);
 764         }
 765
 766         private void OnScrollingChildRelayout(object source, EventArgs args)
 767         {
 768             // Size is changed. Calculate maxScrollDistance.
 769             bool isSizeChanged = previousContainerSize.Width != ContentContainer.Size.Width || previousContainerSize.Height != ContentContainer.Size.Height ||
 770                 previousSize.Width != Size.Width || previousSize.Height != Size.Height;
 771
 772             if (isSizeChanged)
 773             {
 774                 maxScrollDistance = CalculateMaximumScrollDistance();
 775                 SetScrollbar();
 776             }
 777
 778             previousContainerSize = ContentContainer.Size;
 779             previousSize = Size;
 780         }
 781
 782         /// <summary>
 783         /// The composition of a Scrollbar can vary depending on how you use ScrollableBase.
 784         /// Set the composition that will go into the ScrollableBase according to your ScrollableBase.
 785         /// </summary>
 786         /// <since_tizen> 8 </since_tizen>
 787         [EditorBrowsable(EditorBrowsableState.Never)]
 788         protected virtual void SetScrollbar()
 789         {
 790             if (Scrollbar)
 791             {
 792                 bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 793                 float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 794                 float viewportLength = isHorizontal ? Size.Width : Size.Height;
 795                 float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 796                 Scrollbar.Initialize(contentLength, viewportLength, currentPosition, isHorizontal);
 797             }
 798         }
 799
 800         /// <summary>
 801         /// Scrolls to the item at the specified index.
 802         /// </summary>
 803         /// <param name="index">Index of item.</param>
 804         /// <since_tizen> 8 </since_tizen>
 805         public void ScrollToIndex(int index)
 806         {
 807             if (ContentContainer.ChildCount - 1 < index || index < 0)
 808             {
 809                 return;
 810             }
 811
 812             if (SnapToPage)
 813             {
 814                 CurrentPage = index;
 815             }
 816
 817             float targetPosition = Math.Min(ScrollingDirection == Direction.Vertical ? Children[index].Position.Y : Children[index].Position.X, maxScrollDistance);
 818             AnimateChildTo(ScrollDuration, -targetPosition);
 819         }
 820
 821         private void OnScrollDragStarted()
 822         {
 823             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 824             ScrollDragStarted?.Invoke(this, eventArgs);
 825         }
 826
 827         private void OnScrollDragEnded()
 828         {
 829             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 830             ScrollDragEnded?.Invoke(this, eventArgs);
 831         }
 832
 833         private void OnScrollAnimationStarted()
 834         {
 835             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 836             ScrollAnimationStarted?.Invoke(this, eventArgs);
 837         }
 838
 839         private void OnScrollAnimationEnded()
 840         {
 841             scrolling = false;
 842             base.Remove(mInterruptTouchingChild);
 843
 844             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 845             ScrollAnimationEnded?.Invoke(this, eventArgs);
 846         }
 847
 848         private void OnScroll()
 849         {
 850             ScrollEventArgs eventArgs = new ScrollEventArgs(ContentContainer.CurrentPosition);
 851             Scrolling?.Invoke(this, eventArgs);
 852
 853             bool isHorizontal = ScrollingDirection == Direction.Horizontal;
 854             float contentLength = isHorizontal ? ContentContainer.Size.Width : ContentContainer.Size.Height;
 855             float currentPosition = isHorizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y;
 856
 857             scrollBar?.Update(contentLength, Math.Abs(currentPosition));
 858             CheckPreReachedTargetPosition();
 859         }
 860
 861         private void CheckPreReachedTargetPosition()
 862         {
 863             // Check whether we reached pre-reached target position
 864             if (readyToNotice &&
 865                 ContentContainer.CurrentPosition.Y <= finalTargetPosition + NoticeAnimationEndBeforePosition &&
 866                 ContentContainer.CurrentPosition.Y >= finalTargetPosition - NoticeAnimationEndBeforePosition)
 867             {
 868                 //Notice first
 869                 readyToNotice = false;
 870                 OnPreReachedTargetPosition(finalTargetPosition);
 871             }
 872         }
 873
 874         /// <summary>
 875         /// This helps developer who wants to know before scroll is reaching target position.
 876         /// </summary>
 877         /// <param name="targetPosition">Index of item.</param>
 878         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
 879         [EditorBrowsable(EditorBrowsableState.Never)]
 880         protected virtual void OnPreReachedTargetPosition(float targetPosition)
 881         {
 882
 883         }
 884
 885         private void StopScroll()
 886         {
 887             if (scrollAnimation != null)
 888             {
 889                 if (scrollAnimation.State == Animation.States.Playing)
 890                 {
 891                     Debug.WriteLineIf(LayoutDebugScrollableBase, "StopScroll Animation Playing");
 892                     scrollAnimation.Stop(Animation.EndActions.Cancel);
 893                     OnScrollAnimationEnded();
 894                 }
 895                 scrollAnimation.Clear();
 896             }
 897         }
 898
 899         private void AnimateChildTo(int duration, float axisPosition)
 900         {
 901             Debug.WriteLineIf(LayoutDebugScrollableBase, "AnimationTo Animation Duration:" + duration + " Destination:" + axisPosition);
 902             finalTargetPosition = axisPosition;
 903
 904             StopScroll(); // Will replace previous animation so will stop existing one.
 905
 906             if (scrollAnimation == null)
 907             {
 908                 scrollAnimation = new Animation();
 909                 scrollAnimation.Finished += ScrollAnimationFinished;
 910             }
 911
 912             scrollAnimation.Duration = duration;
 913             scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.EaseOutSquare);
 914             scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", axisPosition, ScrollAlphaFunction);
 915             scrolling = true;
 916             OnScrollAnimationStarted();
 917             scrollAnimation.Play();
 918         }
 919
 920         /// <summary>
 921         /// Scroll to specific position with or without animation.
 922         /// </summary>
 923         /// <param name="position">Destination.</param>
 924         /// <param name="animate">Scroll with or without animation</param>
 925         /// <since_tizen> 8 </since_tizen>
 926         public void ScrollTo(float position, bool animate)
 927         {
 928             float currentPositionX = ContentContainer.CurrentPosition.X != 0 ? ContentContainer.CurrentPosition.X : ContentContainer.Position.X;
 929             float currentPositionY = ContentContainer.CurrentPosition.Y != 0 ? ContentContainer.CurrentPosition.Y : ContentContainer.Position.Y;
 930             float delta = ScrollingDirection == Direction.Horizontal ? currentPositionX : currentPositionY;
 931             // The argument position is the new pan position. So the new position of ScrollableBase becomes (-position).
 932             // To move ScrollableBase's position to (-position), it moves by (-position - currentPosition).
 933             delta = -position - delta;
 934
 935             ScrollBy(delta, animate);
 936         }
 937
 938         private float BoundScrollPosition(float targetPosition)
 939         {
 940             if (ScrollAvailableArea != null)
 941             {
 942                 float minScrollPosition = ScrollAvailableArea.X;
 943                 float maxScrollPosition = ScrollAvailableArea.Y;
 944
 945                 targetPosition = Math.Min(-minScrollPosition, targetPosition);
 946                 targetPosition = Math.Max(-maxScrollPosition, targetPosition);
 947             }
 948             else
 949             {
 950                 targetPosition = Math.Min(0, targetPosition);
 951                 targetPosition = Math.Max(-maxScrollDistance, targetPosition);
 952             }
 953
 954             return targetPosition;
 955         }
 956
 957         private void ScrollBy(float displacement, bool animate)
 958         {
 959             if (GetChildCount() == 0 || maxScrollDistance < 0)
 960             {
 961                 return;
 962             }
 963
 964             float childCurrentPosition = (ScrollingDirection == Direction.Horizontal) ? ContentContainer.PositionX : ContentContainer.PositionY;
 965
 966             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy childCurrentPosition:" + childCurrentPosition +
 967                 " displacement:" + displacement,
 968                 " maxScrollDistance:" + maxScrollDistance);
 969
 970             childTargetPosition = childCurrentPosition + displacement; // child current position + gesture displacement
 971
 972             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy currentAxisPosition:" + childCurrentPosition + "childTargetPosition:" + childTargetPosition);
 973
 974             if (animate)
 975             {
 976                 // Calculate scroll animaton duration
 977                 float scrollDistance = Math.Abs(displacement);
 978                 readyToNotice = true;
 979
 980                 AnimateChildTo(ScrollDuration, BoundScrollPosition(AdjustTargetPositionOfScrollAnimation(BoundScrollPosition(childTargetPosition))));
 981             }
 982             else
 983             {
 984                 finalTargetPosition = BoundScrollPosition(childTargetPosition);
 985
 986                 // Set position of scrolling child without an animation
 987                 if (ScrollingDirection == Direction.Horizontal)
 988                 {
 989                     ContentContainer.PositionX = finalTargetPosition;
 990                 }
 991                 else
 992                 {
 993                     ContentContainer.PositionY = finalTargetPosition;
 994                 }
 995             }
 996         }
 997
 998         /// <summary>
 999         /// you can override it to clean-up your own resources.
1000         /// </summary>
1001         /// <param name="type">DisposeTypes</param>
1002         /// This will be public opened in tizen_5.5 after ACR done. Before ACR, need to be hidden as inhouse API.
1003         [EditorBrowsable(EditorBrowsableState.Never)]
1004         protected override void Dispose(DisposeTypes type)
1005         {
1006             if (disposed)
1007             {
1008                 return;
1009             }
1010
1011             if (type == DisposeTypes.Explicit)
1012             {
1013 #if (PROFILE_MOBILE)
1014                 AccessibilityManager.Instance.DeleteAccessibilityAttribute(this);
1015 #endif
1016                 StopVerticalShadowAnimation();
1017                 StopScroll();
1018
1019                 if (mPanGestureDetector != null)
1020                 {
1021                     mPanGestureDetector.Detected -= OnPanGestureDetected;
1022                     mPanGestureDetector.Dispose();
1023                     mPanGestureDetector = null;
1024                 }
1025
1026                 propertyNotification.Dispose();
1027             }
1028             base.Dispose(type);
1029         }
1030
1031         private float CalculateMaximumScrollDistance()
1032         {
1033             float scrollingChildLength = 0;
1034             float scrollerLength = 0;
1035             if (ScrollingDirection == Direction.Horizontal)
1036             {
1037                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Horizontal");
1038
1039                 scrollingChildLength = ContentContainer.Size.Width;
1040                 scrollerLength = Size.Width;
1041             }
1042             else
1043             {
1044                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Vertical");
1045                 scrollingChildLength = ContentContainer.Size.Height;
1046                 scrollerLength = Size.Height;
1047             }
1048
1049             Debug.WriteLineIf(LayoutDebugScrollableBase, "ScrollBy maxScrollDistance:" + (scrollingChildLength - scrollerLength) +
1050                 " parent length:" + scrollerLength +
1051                 " scrolling child length:" + scrollingChildLength);
1052
1053             return Math.Max(scrollingChildLength - scrollerLength, 0);
1054         }
1055
1056         private void PageSnap(float velocity)
1057         {
1058             Debug.WriteLineIf(LayoutDebugScrollableBase, "PageSnap with pan candidate totalDisplacement:" + totalDisplacementForPan +
1059                 " currentPage[" + CurrentPage + "]");
1060
1061             //Increment current page if total displacement enough to warrant a page change.
1062             if (Math.Abs(totalDisplacementForPan) > (mPageWidth * ratioOfScreenWidthToCompleteScroll))
1063             {
1064                 if (totalDisplacementForPan < 0)
1065                 {
1066                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1067                 }
1068                 else
1069                 {
1070                     CurrentPage = Math.Max(0, --CurrentPage);
1071                 }
1072             }
1073             else if (Math.Abs(velocity) > PageFlickThreshold)
1074             {
1075                 if (velocity < 0)
1076                 {
1077                     CurrentPage = Math.Min(Math.Max(Children.Count - 1, 0), ++CurrentPage);
1078                 }
1079                 else
1080                 {
1081                     CurrentPage = Math.Max(0, --CurrentPage);
1082                 }
1083             }
1084
1085             // Animate to new page or reposition to current page
1086             float destinationX = -(Children[CurrentPage].Position.X + Children[CurrentPage].CurrentSize.Width / 2 - CurrentSize.Width / 2); // set to middle of current page
1087             Debug.WriteLineIf(LayoutDebugScrollableBase, "Snapping to page[" + CurrentPage + "] to:" + destinationX + " from:" + ContentContainer.PositionX);
1088             AnimateChildTo(ScrollDuration, destinationX);
1089         }
1090
1091         /// <summary>
1092         /// Enable/Disable overshooting effect. default is disabled.
1093         /// </summary>
1094         [EditorBrowsable(EditorBrowsableState.Never)]
1095         public bool EnableOverShootingEffect { get; set; } = false;
1096
1097         private void AttachShadowView()
1098         {
1099             if (!EnableOverShootingEffect)
1100                 return;
1101
1102             if (ScrollingDirection != Direction.Vertical)
1103                 return;
1104
1105             // stop animation if necessary.
1106             StopVerticalShadowAnimation();
1107
1108             base.Add(verticalTopShadowView);
1109             base.Add(verticalBottomShadowView);
1110
1111             verticalTopShadowView.Size = new Size(SizeWidth, 0.0f);
1112             verticalTopShadowView.Opacity = 1.0f;
1113             verticalTopShadowView.RaiseToTop();
1114
1115             verticalBottomShadowView.Size = new Size(SizeWidth, 0.0f);
1116             verticalBottomShadowView.Opacity = 1.0f;
1117             verticalBottomShadowView.RaiseToTop();
1118
1119             // at the beginning, height of vertical shadow is 0, so it is invisible.
1120             isVerticalShadowShown = false;
1121         }
1122
1123         private void DragVerticalShadow(float totalPanDisplacement, float panDisplacement)
1124         {
1125             if (!EnableOverShootingEffect)
1126                 return;
1127
1128             if (ScrollingDirection != Direction.Vertical)
1129                 return;
1130
1131             if (totalPanDisplacement > 0) // downwards
1132             {
1133                 // check if reaching at the top.
1134                 if ((int)finalTargetPosition != 0)
1135                 {
1136                     isVerticalShadowShown = false;
1137                     return;
1138                 }
1139
1140                 // save start displacement, and re-calculate displacement.
1141                 if (!isVerticalShadowShown)
1142                 {
1143                     startShowShadowDisplacement = totalPanDisplacement;
1144                 }
1145                 isVerticalShadowShown = true;
1146
1147                 // trigger event
1148                 ScrollOutOfBoundWithDisplacementEventArgs.Direction direction = panDisplacement > 0 ?
1149                     ScrollOutOfBoundWithDisplacementEventArgs.Direction.Down : ScrollOutOfBoundWithDisplacementEventArgs.Direction.Up;
1150                 OnScrollOutOfBoundWithDisplacement(direction, totalPanDisplacement);
1151
1152                 float newDisplacement = (int)totalPanDisplacement < (int)startShowShadowDisplacement ? 0 : totalPanDisplacement - startShowShadowDisplacement;
1153
1154                 // scale limit of width is 60%.
1155                 float widthScale = newDisplacement / verticalShadowScaleHeightLimit;
1156                 verticalTopShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1157
1158                 // scale limit of height is 300%.
1159                 verticalTopShadowView.SizeHeight = newDisplacement > verticalShadowScaleHeightLimit ? verticalShadowScaleHeightLimit : newDisplacement;
1160             }
1161             else if (totalPanDisplacement < 0) // upwards
1162             {
1163                 // check if reaching at the bottom.
1164                 if (-(int)finalTargetPosition != (int)maxScrollDistance)
1165                 {
1166                     isVerticalShadowShown = false;
1167                     return;
1168                 }
1169
1170                 // save start displacement, and re-calculate displacement.
1171                 if (!isVerticalShadowShown)
1172                 {
1173                     startShowShadowDisplacement = totalPanDisplacement;
1174                 }
1175                 isVerticalShadowShown = true;
1176
1177                 // trigger event
1178                 ScrollOutOfBoundWithDisplacementEventArgs.Direction direction = panDisplacement > 0 ?
1179                     ScrollOutOfBoundWithDisplacementEventArgs.Direction.Down : ScrollOutOfBoundWithDisplacementEventArgs.Direction.Up;
1180                 OnScrollOutOfBoundWithDisplacement(direction, totalPanDisplacement);
1181
1182                 float newDisplacement = (int)startShowShadowDisplacement < (int)totalPanDisplacement ? 0 : startShowShadowDisplacement - totalPanDisplacement;
1183
1184                 // scale limit of width is 60%.
1185                 float widthScale = newDisplacement / verticalShadowScaleHeightLimit;
1186                 verticalBottomShadowView.SizeWidth = widthScale > 0.6f ? SizeWidth * 0.4f : SizeWidth * (1.0f - widthScale);
1187
1188                 // scale limit of height is 300%.
1189                 verticalBottomShadowView.SizeHeight = newDisplacement > verticalShadowScaleHeightLimit ? verticalShadowScaleHeightLimit : newDisplacement;
1190             }
1191             else
1192             {
1193                 // if total displacement is 0, shadow would become invisible.
1194                 isVerticalShadowShown = false;
1195             }
1196         }
1197
1198         private void PlayVerticalShadowAnimation()
1199         {
1200             if (!EnableOverShootingEffect)
1201                 return;
1202
1203             if (ScrollingDirection != Direction.Vertical)
1204                 return;
1205
1206             // stop animation if necessary.
1207             StopVerticalShadowAnimation();
1208
1209             if (verticalShadowAnimation == null)
1210             {
1211                 verticalShadowAnimation = new Animation(verticalShadowAnimationDuration);
1212                 verticalShadowAnimation.Finished += OnVerticalShadowAnimationFinished;
1213             }
1214
1215             View targetView = totalDisplacementForPan < 0 ? verticalBottomShadowView : verticalTopShadowView;
1216             verticalShadowAnimation.AnimateTo(targetView, "SizeWidth", SizeWidth);
1217             verticalShadowAnimation.AnimateTo(targetView, "SizeHeight", 0.0f);
1218             verticalShadowAnimation.AnimateTo(targetView, "Opacity", 0.0f);
1219             verticalShadowAnimation.Play();
1220         }
1221
1222         private void StopVerticalShadowAnimation()
1223         {
1224             if (verticalShadowAnimation == null || verticalShadowAnimation.State != Animation.States.Playing)
1225                 return;
1226
1227             verticalShadowAnimation.Stop(Animation.EndActions.Cancel);
1228             OnVerticalShadowAnimationFinished(null, null);
1229             verticalShadowAnimation.Clear();
1230         }
1231
1232         private void OnVerticalShadowAnimationFinished(object sender, EventArgs e)
1233         {
1234             base.Remove(verticalTopShadowView);
1235             base.Remove(verticalBottomShadowView);
1236
1237             verticalTopShadowView.Size = new Size(SizeWidth, 0.0f);
1238             verticalBottomShadowView.Size = new Size(SizeWidth, 0.0f);
1239
1240             // after animation finished, height & opacity of vertical shadow both are 0, so it is invisible.
1241             isVerticalShadowShown = false;
1242         }
1243
1244         private void OnScrollOutOfBoundWithDisplacement(ScrollOutOfBoundWithDisplacementEventArgs.Direction direction, float displacement)
1245         {
1246             ScrollOutOfBoundWithDisplacementEventArgs args = new ScrollOutOfBoundWithDisplacementEventArgs(direction, displacement);
1247             ScrollOutOfBoundWithDisplacement?.Invoke(this, args);
1248         }
1249
1250         private void OnPanGestureDetected(object source, PanGestureDetector.DetectedEventArgs e)
1251         {
1252             OnPanGesture(e.PanGesture);
1253         }
1254
1255         private void OnPanGesture(PanGesture panGesture)
1256         {
1257             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1258             {
1259                 return;
1260             }
1261
1262             if (panGesture.State == Gesture.StateType.Started)
1263             {
1264                 readyToNotice = false;
1265                 base.Add(mInterruptTouchingChild);
1266                 AttachShadowView();
1267                 Debug.WriteLineIf(LayoutDebugScrollableBase, "Gesture Start");
1268                 if (scrolling && !SnapToPage)
1269                 {
1270                     StopScroll();
1271                 }
1272                 totalDisplacementForPan = 0.0f;
1273                 OnScrollDragStarted();
1274             }
1275             else if (panGesture.State == Gesture.StateType.Continuing)
1276             {
1277                 if (ScrollingDirection == Direction.Horizontal)
1278                 {
1279                     ScrollBy(panGesture.Displacement.X, false);
1280                     totalDisplacementForPan += panGesture.Displacement.X;
1281                 }
1282                 else
1283                 {
1284                     // if vertical shadow is shown, does not scroll.
1285                     if (!isVerticalShadowShown)
1286                     {
1287                         ScrollBy(panGesture.Displacement.Y, false);
1288                     }
1289                     totalDisplacementForPan += panGesture.Displacement.Y;
1290                     DragVerticalShadow(totalDisplacementForPan, panGesture.Displacement.Y);
1291                 }
1292                 Debug.WriteLineIf(LayoutDebugScrollableBase, "OnPanGestureDetected Continue totalDisplacementForPan:" + totalDisplacementForPan);
1293             }
1294             else if (panGesture.State == Gesture.StateType.Finished || panGesture.State == Gesture.StateType.Cancelled)
1295             {
1296                 PlayVerticalShadowAnimation();
1297                 OnScrollDragEnded();
1298                 StopScroll(); // Will replace previous animation so will stop existing one.
1299
1300                 if (scrollAnimation == null)
1301                 {
1302                     scrollAnimation = new Animation();
1303                     scrollAnimation.Finished += ScrollAnimationFinished;
1304                 }
1305
1306                 float panVelocity = (ScrollingDirection == Direction.Horizontal) ? panGesture.Velocity.X : panGesture.Velocity.Y;
1307
1308                 if (SnapToPage)
1309                 {
1310                     PageSnap(panVelocity);
1311                 }
1312                 else
1313                 {
1314                     if (panVelocity == 0)
1315                     {
1316                         float currentScrollPosition = (ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1317                         scrollAnimation.DefaultAlphaFunction = new AlphaFunction(AlphaFunction.BuiltinFunctions.Linear);
1318                         scrollAnimation.Duration = 0;
1319                         scrollAnimation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", currentScrollPosition);
1320                         scrollAnimation.Play();
1321                     }
1322                     else
1323                     {
1324                         Decelerating(panVelocity, scrollAnimation);
1325                     }
1326                 }
1327
1328                 totalDisplacementForPan = 0;
1329                 scrolling = true;
1330                 readyToNotice = true;
1331                 OnScrollAnimationStarted();
1332             }
1333         }
1334
1335         internal override bool OnAccessibilityPan(PanGesture gestures)
1336         {
1337             if (SnapToPage && scrollAnimation != null && scrollAnimation.State == Animation.States.Playing)
1338             {
1339                 return false;
1340             }
1341
1342             OnPanGesture(gestures);
1343             return true;
1344         }
1345
1346         private float CustomScrollAlphaFunction(float progress)
1347         {
1348             if (panAnimationDelta == 0)
1349             {
1350                 return 1.0f;
1351             }
1352             else
1353             {
1354                 // Parameter "progress" is normalized value. We need to multiply target duration to calculate distance.
1355                 // Can get real distance using equation of deceleration (check Decelerating function)
1356                 // After get real distance, normalize it
1357                 float realDuration = progress * panAnimationDuration;
1358                 float realDistance = velocityOfLastPan * ((float)Math.Pow(decelerationRate, realDuration) - 1) / logValueOfDeceleration;
1359                 float result = Math.Min(realDistance / Math.Abs(panAnimationDelta), 1.0f);
1360                 return result;
1361             }
1362         }
1363
1364         /// <summary>
1365         /// you can override it to custom your decelerating
1366         /// </summary>
1367         /// <param name="velocity">Velocity of current pan.</param>
1368         /// <param name="animation">Scroll animation.</param>
1369         [EditorBrowsable(EditorBrowsableState.Never)]
1370         protected virtual void Decelerating(float velocity, Animation animation)
1371         {
1372             // Decelerating using deceleration equation ===========
1373             //
1374             // V   : velocity (pixel per milisecond)
1375             // V0  : initial velocity
1376             // d   : deceleration rate,
1377             // t   : time
1378             // X   : final position after decelerating
1379             // log : natural logarithm
1380             //
1381             // V(t) = V0 * d pow t;
1382             // X(t) = V0 * (d pow t - 1) / log d;  <-- Integrate the velocity function
1383             // X(∞) = V0 * d / (1 - d); <-- Result using inifit T can be final position because T is tending to infinity.
1384             //
1385             // Because of final T is tending to inifity, we should use threshold value to finish.
1386             // Final T = log(-threshold * log d / |V0| ) / log d;
1387
1388             velocityOfLastPan = Math.Abs(velocity);
1389
1390             float currentScrollPosition = -(ScrollingDirection == Direction.Horizontal ? ContentContainer.CurrentPosition.X : ContentContainer.CurrentPosition.Y);
1391             panAnimationDelta = (velocityOfLastPan * decelerationRate) / (1 - decelerationRate);
1392             panAnimationDelta = velocity > 0 ? -panAnimationDelta : panAnimationDelta;
1393
1394             float destination = -(panAnimationDelta + currentScrollPosition);
1395             float adjustDestination = AdjustTargetPositionOfScrollAnimation(destination);
1396             float maxPosition = ScrollAvailableArea != null ? ScrollAvailableArea.Y : maxScrollDistance;
1397             float minPosition = ScrollAvailableArea != null ? ScrollAvailableArea.X : 0;
1398
1399             if (destination < -maxPosition || destination > minPosition)
1400             {
1401                 panAnimationDelta = velocity > 0 ? (currentScrollPosition - minPosition) : (maxPosition - currentScrollPosition);
1402                 destination = velocity > 0 ? minPosition : -maxPosition;
1403
1404                 if (panAnimationDelta == 0)
1405                 {
1406                     panAnimationDuration = 0.0f;
1407                 }
1408                 else
1409                 {
1410                     panAnimationDuration = (float)Math.Log((panAnimationDelta * logValueOfDeceleration / velocityOfLastPan + 1), decelerationRate);
1411                 }
1412
1413                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1414                     "OverRange======================= \n" +
1415                     "[decelerationRate] " + decelerationRate + "\n" +
1416                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1417                     "[Velocity] " + velocityOfLastPan + "\n" +
1418                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1419                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1420                     "[Destination] " + destination + "\n" +
1421                     "[Duration] " + panAnimationDuration + "\n" +
1422                     "================================ \n"
1423                 );
1424             }
1425             else
1426             {
1427                 panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1428
1429                 if (adjustDestination != destination)
1430                 {
1431                     destination = adjustDestination;
1432                     panAnimationDelta = destination + currentScrollPosition;
1433                     velocityOfLastPan = Math.Abs(panAnimationDelta * logValueOfDeceleration / ((float)Math.Pow(decelerationRate, panAnimationDuration) - 1));
1434                     panAnimationDuration = (float)Math.Log(-DecelerationThreshold * logValueOfDeceleration / velocityOfLastPan) / logValueOfDeceleration;
1435                 }
1436
1437                 Debug.WriteLineIf(LayoutDebugScrollableBase, "\n" +
1438                     "================================ \n" +
1439                     "[decelerationRate] " + decelerationRate + "\n" +
1440                     "[logValueOfDeceleration] " + logValueOfDeceleration + "\n" +
1441                     "[Velocity] " + velocityOfLastPan + "\n" +
1442                     "[CurrentPosition] " + currentScrollPosition + "\n" +
1443                     "[CandidateDelta] " + panAnimationDelta + "\n" +
1444                     "[Destination] " + destination + "\n" +
1445                     "[Duration] " + panAnimationDuration + "\n" +
1446                     "================================ \n"
1447                 );
1448             }
1449
1450             finalTargetPosition = destination;
1451
1452             customScrollAlphaFunction = new UserAlphaFunctionDelegate(CustomScrollAlphaFunction);
1453             animation.DefaultAlphaFunction = new AlphaFunction(customScrollAlphaFunction);
1454             GC.KeepAlive(customScrollAlphaFunction);
1455             animation.Duration = (int)panAnimationDuration;
1456             animation.AnimateTo(ContentContainer, (ScrollingDirection == Direction.Horizontal) ? "PositionX" : "PositionY", destination);
1457             animation.Play();
1458         }
1459
1460         private void ScrollAnimationFinished(object sender, EventArgs e)
1461         {
1462             OnScrollAnimationEnded();
1463         }
1464
1465         /// <summary>
1466         /// Adjust scrolling position by own scrolling rules.
1467         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1468         /// </summary>
1469         /// This may be public opened in tizen_6.0 after ACR done. Before ACR, need to be hidden as inhouse API
1470         [EditorBrowsable(EditorBrowsableState.Never)]
1471         protected virtual float AdjustTargetPositionOfScrollAnimation(float position)
1472         {
1473             return position;
1474         }
1475
1476         /// <summary>
1477         /// Scroll position given to ScrollTo.
1478         /// This is the position in the opposite direction to the position of ContentContainer.
1479         /// </summary>
1480         /// <since_tizen> 8 </since_tizen>
1481         public Position ScrollPosition
1482         {
1483             get
1484             {
1485                 return new Position(-ContentContainer.Position);
1486             }
1487         }
1488
1489         /// <summary>
1490         /// Current scroll position in the middle of ScrollTo animation.
1491         /// This is the position in the opposite direction to the current position of ContentContainer.
1492         /// </summary>
1493         /// <since_tizen> 8 </since_tizen>
1494         public Position ScrollCurrentPosition
1495         {
1496             get
1497             {
1498                 return new Position(-ContentContainer.CurrentPosition);
1499             }
1500         }
1501
1502         /// <summary>
1503         /// Remove all children in ContentContainer.
1504         /// </summary>
1505         /// <param name="dispose">If true, removed child is disposed.</param>
1506         [EditorBrowsable(EditorBrowsableState.Never)]
1507         public void RemoveAllChildren(bool dispose = false)
1508         {
1509             RecursiveRemoveChildren(ContentContainer, dispose);
1510         }
1511
1512         private void RecursiveRemoveChildren(View parent, bool dispose)
1513         {
1514             if (parent == null)
1515             {
1516                 return;
1517             }
1518             int maxChild = (int)parent.GetChildCount();
1519             for (int i = maxChild - 1; i >= 0; --i)
1520             {
1521                 View child = parent.GetChildAt((uint)i);
1522                 if (child == null)
1523                 {
1524                     continue;
1525                 }
1526                 RecursiveRemoveChildren(child, dispose);
1527                 parent.Remove(child);
1528                 if (dispose)
1529                 {
1530                     child.Dispose();
1531                 }
1532             }
1533         }
1534
1535     }
1536
1537 } // namespace