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