src/Tizen.NUI.Components/Controls/RecyclerView/CollectionView.cs

   1 /* Copyright (c) 2021 Samsung Electronics Co., Ltd.
   2  *
   3  * Licensed under the Apache License, Version 2.0 (the "License");
   4  * you may not use this file except in compliance with the License.
   5  * You may obtain a copy of the License at
   6  *
   7  * http://www.apache.org/licenses/LICENSE-2.0
   8  *
   9  * Unless required by applicable law or agreed to in writing, software
  10  * distributed under the License is distributed on an "AS IS" BASIS,
  11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12  * See the License for the specific language governing permissions and
  13  * limitations under the License.
  14  *
  15  */
  16 using System;
  17 using System.Linq;
  18 using System.Collections;
  19 using System.Collections.Generic;
  20 using System.Collections.Specialized;
  21 using System.Windows.Input;
  22 using System.ComponentModel;
  23 using Tizen.NUI.BaseComponents;
  24 using Tizen.NUI.Binding;
  25
  26 namespace Tizen.NUI.Components
  27 {
  28     /// <summary>
  29     /// Selectable RecyclerView that presenting a collection of items with variable layouters.
  30     /// </summary>
  31     /// <since_tizen> 9 </since_tizen>
  32     public class CollectionView : RecyclerView
  33     {
  34         /// <summary>
  35         /// Binding Property of selected item in single selection.
  36         /// </summary>
  37         /// <since_tizen> 9 </since_tizen>
  38         public static readonly BindableProperty SelectedItemProperty =
  39             BindableProperty.Create(nameof(SelectedItem), typeof(object), typeof(CollectionView), null,
  40                 propertyChanged: (bindable, oldValue, newValue) =>
  41                 {
  42                     var colView = (CollectionView)bindable;
  43                     oldValue = colView.selectedItem;
  44                     colView.selectedItem = newValue;
  45                     var args = new SelectionChangedEventArgs(oldValue, newValue);
  46
  47                     foreach (RecyclerViewItem item in colView.ContentContainer.Children.Where((item) => item is RecyclerViewItem))
  48                     {
  49                         if (item.BindingContext == null) continue;
  50                         if (item.BindingContext == oldValue) item.IsSelected = false;
  51                         else if (item.BindingContext == newValue) item.IsSelected = true;
  52                     }
  53
  54                     SelectionPropertyChanged(colView, args);
  55                 },
  56                 defaultValueCreator: (bindable) =>
  57                 {
  58                     var colView = (CollectionView)bindable;
  59                     return colView.selectedItem;
  60                 });
  61
  62         /// <summary>
  63         /// Binding Property of selected items list in multiple selection.
  64         /// </summary>
  65         /// <since_tizen> 9 </since_tizen>
  66         public static readonly BindableProperty SelectedItemsProperty =
  67             BindableProperty.Create(nameof(SelectedItems), typeof(IList<object>), typeof(CollectionView), null,
  68                 propertyChanged: (bindable, oldValue, newValue) =>
  69                 {
  70                     var colView = (CollectionView)bindable;
  71                     var oldSelection = colView.selectedItems ?? selectEmpty;
  72                     //FIXME : CoerceSelectedItems calls only isCreatedByXaml
  73                     var newSelection = (SelectionList)CoerceSelectedItems(colView, newValue);
  74                     colView.selectedItems = newSelection;
  75                     colView.SelectedItemsPropertyChanged(oldSelection, newSelection);
  76                 },
  77                 defaultValueCreator: (bindable) =>
  78                 {
  79                     var colView = (CollectionView)bindable;
  80                     colView.selectedItems = colView.selectedItems ?? new SelectionList(colView);
  81                     return colView.selectedItems;
  82                 });
  83
  84         /// <summary>
  85         /// Binding Property of selected items list in multiple selection.
  86         /// </summary>
  87         /// <since_tizen> 9 </since_tizen>
  88         public static readonly BindableProperty SelectionModeProperty =
  89             BindableProperty.Create(nameof(SelectionMode), typeof(ItemSelectionMode), typeof(CollectionView), ItemSelectionMode.None,
  90                 propertyChanged: (bindable, oldValue, newValue) =>
  91                 {
  92                     var colView = (CollectionView)bindable;
  93                     oldValue = colView.selectionMode;
  94                     colView.selectionMode = (ItemSelectionMode)newValue;
  95                     SelectionModePropertyChanged(colView, oldValue, newValue);
  96                 },
  97                 defaultValueCreator: (bindable) =>
  98                 {
  99                     var colView = (CollectionView)bindable;
 100                     return colView.selectionMode;
 101                 });
 102
 103         /// <summary>
 104         /// Binding Property of items data source.
 105         /// </summary>
 106         [EditorBrowsable(EditorBrowsableState.Never)]
 107         public static readonly BindableProperty ItemsSourceProperty =
 108             BindableProperty.Create(nameof(ItemsSource), typeof(IEnumerable), typeof(CollectionView), null,
 109                 propertyChanged: (bindable, oldValue, newValue) =>
 110                 {
 111                     var colView = (CollectionView)bindable;
 112                     oldValue = colView.itemsSource;
 113
 114                     if (oldValue != null)
 115                     {
 116                         // Clearing old data!
 117                         if (oldValue is INotifyCollectionChanged prevNotifyCollectionChanged)
 118                         {
 119                             prevNotifyCollectionChanged.CollectionChanged -= colView.CollectionChanged;
 120                         }
 121                         if (colView.selectedItem != null) colView.selectedItem = null;
 122                         colView.selectedItems?.Clear();
 123                     }
 124
 125                     colView.itemsSource = (IEnumerable)newValue;
 126
 127                     if (newValue == null)
 128                     {
 129                         colView.InternalItemSource?.Dispose();
 130                         colView.InternalItemSource = null;
 131                         colView.itemsLayouter?.Clear();
 132                         colView.ClearCache();
 133                         return;
 134                     }
 135                     if (newValue is INotifyCollectionChanged newNotifyCollectionChanged)
 136                     {
 137                         newNotifyCollectionChanged.CollectionChanged += colView.CollectionChanged;
 138                     }
 139
 140                     colView.InternalItemSource?.Dispose();
 141                     colView.InternalItemSource = ItemsSourceFactory.Create(colView);
 142
 143                     if (colView.itemsLayouter == null) return;
 144
 145                     colView.needInitalizeLayouter = true;
 146                     colView.Init();
 147                 },
 148                 defaultValueCreator: (bindable) =>
 149                 {
 150                     var colView = (CollectionView)bindable;
 151                     return colView.itemsSource;
 152                 });
 153
 154
 155         private static readonly IList<object> selectEmpty = new List<object>(0);
 156         private DataTemplate itemTemplate = null;
 157         private IEnumerable itemsSource = null;
 158         private ItemsLayouter itemsLayouter = null;
 159         private DataTemplate groupHeaderTemplate;
 160         private DataTemplate groupFooterTemplate;
 161         private bool isGrouped;
 162         private bool wasRelayouted = false;
 163         private bool needInitalizeLayouter = false;
 164         private object selectedItem;
 165         private SelectionList selectedItems;
 166         private bool suppressSelectionChangeNotification;
 167         private ItemSelectionMode selectionMode = ItemSelectionMode.None;
 168         private RecyclerViewItem header;
 169         private RecyclerViewItem footer;
 170         private View focusedView;
 171         private int prevFocusedDataIndex = 0;
 172         private List<RecyclerViewItem> recycleGroupHeaderCache { get; } = new List<RecyclerViewItem>();
 173         private List<RecyclerViewItem> recycleGroupFooterCache { get; } = new List<RecyclerViewItem>();
 174         private bool delayedScrollTo;
 175         private (float position, bool anim) delayedScrollToParam;
 176
 177         private bool delayedIndexScrollTo;
 178         private (int index, bool anim, ItemScrollTo scrollTo) delayedIndexScrollToParam;
 179
 180         /// <summary>
 181         /// Base constructor.
 182         /// </summary>
 183         /// <since_tizen> 9 </since_tizen>
 184         public CollectionView() : base()
 185         {
 186             FocusGroup = true;
 187             SetKeyboardNavigationSupport(true);
 188         }
 189
 190         /// <summary>
 191         /// Base constructor with ItemsSource
 192         /// </summary>
 193         /// <param name="itemsSource">item's data source</param>
 194         /// <since_tizen> 9 </since_tizen>
 195         public CollectionView(IEnumerable itemsSource) : this()
 196         {
 197             ItemsSource = itemsSource;
 198         }
 199
 200         /// <summary>
 201         /// Base constructor with ItemsSource, ItemsLayouter and ItemTemplate
 202         /// </summary>
 203         /// <param name="itemsSource">item's data source</param>
 204         /// <param name="layouter">item's layout manager</param>
 205         /// <param name="template">item's view template with data bindings</param>
 206         [EditorBrowsable(EditorBrowsableState.Never)]
 207         public CollectionView(IEnumerable itemsSource, ItemsLayouter layouter, DataTemplate template) : this()
 208         {
 209             ItemsSource = itemsSource;
 210             ItemTemplate = template;
 211             ItemsLayouter = layouter;
 212         }
 213
 214         /// <summary>
 215         /// Event of Selection changed.
 216         /// previous selection list and current selection will be provided.
 217         /// </summary>
 218         /// <since_tizen> 9 </since_tizen>
 219         public event EventHandler<SelectionChangedEventArgs> SelectionChanged;
 220
 221         /// <summary>
 222         /// Align item in the viewport when ScrollTo() calls.
 223         /// </summary>
 224         /// <since_tizen> 9 </since_tizen>
 225         public enum ItemScrollTo
 226         {
 227             /// <summary>
 228             /// Scroll to show item in nearest viewport on scroll direction.
 229             /// item is above the scroll viewport, item will be came into front,
 230             /// item is under the scroll viewport, item will be came into end,
 231             /// item is in the scroll viewport, no scroll.
 232             /// </summary>
 233             /// <since_tizen> 9 </since_tizen>
 234             Nearest,
 235             /// <summary>
 236             /// Scroll to show item in start of the viewport.
 237             /// </summary>
 238             /// <since_tizen> 9 </since_tizen>
 239             Start,
 240             /// <summary>
 241             /// Scroll to show item in center of the viewport.
 242             /// </summary>
 243             /// <since_tizen> 9 </since_tizen>
 244             Center,
 245             /// <summary>
 246             /// Scroll to show item in end of the viewport.
 247             /// </summary>
 248             /// <since_tizen> 9 </since_tizen>
 249             End,
 250         }
 251
 252         /// <summary>
 253         /// Item's source data in IEnumerable.
 254         /// </summary>
 255         /// <since_tizen> 9 </since_tizen>
 256         public override IEnumerable ItemsSource
 257         {
 258             get => (IEnumerable)GetValue(ItemsSourceProperty);
 259             set => SetValue(ItemsSourceProperty, value);
 260         }
 261
 262         /// <summary>
 263         /// DataTemplate for items.
 264         /// Create visual contents and binding properties.
 265         /// return object type is restricted RecyclerViewItem.
 266         /// <seealso cref="Tizen.NUI.Binding.DataTemplate" />
 267         /// </summary>
 268         /// <since_tizen> 9 </since_tizen>
 269         public override DataTemplate ItemTemplate
 270         {
 271             get
 272             {
 273                 return itemTemplate;
 274             }
 275             set
 276             {
 277                 itemTemplate = value;
 278                 if (value == null)
 279                 {
 280                     return;
 281                 }
 282
 283                 needInitalizeLayouter = true;
 284                 Init();
 285             }
 286         }
 287
 288         /// <summary>
 289         /// Items Layouter.
 290         /// Layouting items on the scroll ContentContainer.
 291         /// <seealso cref="ItemsLayouter" />
 292         /// <seealso cref="LinearLayouter" />
 293         /// <seealso cref="GridLayouter" />
 294         /// </summary>
 295         /// <since_tizen> 9 </since_tizen>
 296         public virtual ItemsLayouter ItemsLayouter
 297         {
 298             get
 299             {
 300                 return itemsLayouter;
 301             }
 302             set
 303             {
 304                 itemsLayouter?.Clear();
 305                 ClearCache();
 306
 307                 itemsLayouter = value;
 308                 base.InternalItemsLayouter = itemsLayouter;
 309                 if (value == null)
 310                 {
 311                     needInitalizeLayouter = false;
 312                     return;
 313                 }
 314
 315                 needInitalizeLayouter = true;
 316
 317                 var styleName = "Tizen.NUI.Components." + (itemsLayouter is LinearLayouter? "LinearLayouter" : (itemsLayouter is GridLayouter ? "GridLayouter" : "ItemsLayouter"));
 318                 ViewStyle layouterStyle = ThemeManager.GetStyle(styleName);
 319                 if (layouterStyle != null)
 320                 {
 321                     itemsLayouter.Padding = new Extents(layouterStyle.Padding);
 322                 }
 323                 Init();
 324             }
 325         }
 326
 327         /// <summary>
 328         /// Scrolling direction to display items layout.
 329         /// </summary>
 330         /// <since_tizen> 9 </since_tizen>
 331         public new Direction ScrollingDirection
 332         {
 333             get
 334             {
 335                 return base.ScrollingDirection;
 336             }
 337             set
 338             {
 339                 if (base.ScrollingDirection != value)
 340                 {
 341                     base.ScrollingDirection = value;
 342                     needInitalizeLayouter = true;
 343                     Init();
 344                 }
 345             }
 346         }
 347
 348         /// <summary>
 349         /// Selected item in single selection.
 350         /// </summary>
 351         /// <since_tizen> 9 </since_tizen>
 352         public object SelectedItem
 353         {
 354             get => GetValue(SelectedItemProperty);
 355             set => SetValue(SelectedItemProperty, value);
 356         }
 357
 358         /// <summary>
 359         /// Selected items list in multiple selection.
 360         /// </summary>
 361         /// <since_tizen> 9 </since_tizen>
 362         public IList<object> SelectedItems
 363         {
 364             get => (IList<object>)GetValue(SelectedItemsProperty);
 365             // set => SetValue(SelectedItemsProperty, new SelectionList(this, value));
 366         }
 367
 368         /// <summary>
 369         /// Selection mode to handle items selection. See ItemSelectionMode for details.
 370         /// </summary>
 371         /// <since_tizen> 9 </since_tizen>
 372         public ItemSelectionMode SelectionMode
 373         {
 374             get => (ItemSelectionMode)GetValue(SelectionModeProperty);
 375             set => SetValue(SelectionModeProperty, value);
 376         }
 377
 378         /// <summary>
 379         /// Command of selection changed.
 380         /// </summary>
 381         [EditorBrowsable(EditorBrowsableState.Never)]
 382         public ICommand SelectionChangedCommand { set; get; }
 383
 384         /// <summary>
 385         /// Command parameter of selection changed.
 386         /// </summary>
 387         [EditorBrowsable(EditorBrowsableState.Never)]
 388         public object SelectionChangedCommandParameter { set; get; }
 389
 390         /// <summary>
 391         /// Header item placed in top-most position.
 392         /// </summary>
 393         /// <remarks>Please note that, internal index will be increased by header.</remarks>
 394         /// <since_tizen> 9 </since_tizen>
 395         public RecyclerViewItem Header
 396         {
 397             get => header;
 398             set
 399             {
 400                 if (header != null)
 401                 {
 402                     //ContentContainer.Remove(header);
 403                     Utility.Dispose(header);
 404                 }
 405                 if (value != null)
 406                 {
 407                     value.Index = 0;
 408                     value.ParentItemsView = this;
 409                     value.IsHeader = true;
 410                     ContentContainer.Add(value);
 411                 }
 412                 header = value;
 413                 if (InternalItemSource != null)
 414                 {
 415                     InternalItemSource.HasHeader = (value != null);
 416                 }
 417                 needInitalizeLayouter = true;
 418                 Init();
 419             }
 420         }
 421
 422         /// <summary>
 423         /// Footer item placed in bottom-most position.
 424         /// </summary>
 425         /// <remarks>Please note that, internal index will be increased by footer.</remarks>
 426         /// <since_tizen> 9 </since_tizen>
 427         public RecyclerViewItem Footer
 428         {
 429             get => footer;
 430             set
 431             {
 432                 if (footer != null)
 433                 {
 434                     //ContentContainer.Remove(footer);
 435                     Utility.Dispose(footer);
 436                 }
 437                 if (value != null)
 438                 {
 439                     value.Index = InternalItemSource?.Count ?? 0;
 440                     value.ParentItemsView = this;
 441                     value.IsFooter = true;
 442                     ContentContainer.Add(value);
 443                 }
 444                 footer = value;
 445                 if (InternalItemSource != null)
 446                 {
 447                     InternalItemSource.HasFooter = (value != null);
 448                 }
 449                 needInitalizeLayouter = true;
 450                 Init();
 451             }
 452         }
 453
 454         /// <summary>
 455         /// Enable groupable view.
 456         /// </summary>
 457         [EditorBrowsable(EditorBrowsableState.Never)]
 458         public bool IsGrouped
 459         {
 460             get => isGrouped;
 461             internal set
 462             {
 463                 if (isGrouped != value)
 464                 {
 465                     isGrouped = value;
 466                     //Need to re-intialize Internal Item Source.
 467                     if (InternalItemSource != null)
 468                     {
 469                         InternalItemSource.Dispose();
 470                         InternalItemSource = null;
 471                     }
 472                     if (ItemsSource != null)
 473                         InternalItemSource = ItemsSourceFactory.Create(this);
 474                 }
 475                 needInitalizeLayouter = true;
 476                 Init();
 477             }
 478         }
 479
 480         /// <summary>
 481         ///  DataTemplate of group header.
 482         /// </summary>
 483         /// <remarks>Please note that, internal index will be increased by group header.
 484         /// GroupHeaderTemplate is essential for groupable view.</remarks>
 485         [EditorBrowsable(EditorBrowsableState.Never)]
 486         public DataTemplate GroupHeaderTemplate
 487         {
 488             get
 489             {
 490                 return groupHeaderTemplate;
 491             }
 492             set
 493             {
 494                 groupHeaderTemplate = value;
 495                 if (value != null) IsGrouped = true;
 496                 else IsGrouped = false;
 497             }
 498         }
 499
 500         /// <summary>
 501         /// DataTemplate of group footer. Group feature is not supported yet.
 502         /// </summary>
 503         /// <remarks>Please note that, internal index will be increased by group footer.</remarks>
 504         [EditorBrowsable(EditorBrowsableState.Never)]
 505         public DataTemplate GroupFooterTemplate
 506         {
 507             get
 508             {
 509                 return groupFooterTemplate;
 510             }
 511             set
 512             {
 513                 groupFooterTemplate = value;
 514                 needInitalizeLayouter = true;
 515                 //Need to re-intialize Internal Item Source.
 516                 if (InternalItemSource != null)
 517                 {
 518                     InternalItemSource.Dispose();
 519                     InternalItemSource = null;
 520                 }
 521                 if (ItemsSource != null)
 522                     InternalItemSource = ItemsSourceFactory.Create(this);
 523                 Init();
 524             }
 525         }
 526
 527         /// <summary>
 528         /// Internal encapsulated items data source.
 529         /// </summary>
 530         internal new IGroupableItemSource InternalItemSource
 531         {
 532             get
 533             {
 534                 return (base.InternalItemSource as IGroupableItemSource);
 535             }
 536             set
 537             {
 538                 base.InternalItemSource = value;
 539             }
 540         }
 541
 542         /// <summary>
 543         /// Size strategy of measuring scroll content. see details in ItemSizingStrategy.
 544         /// </summary>
 545         [EditorBrowsable(EditorBrowsableState.Never)]
 546         internal ItemSizingStrategy SizingStrategy { get; set; }
 547
 548         /// <inheritdoc/>
 549         /// <since_tizen> 9 </since_tizen>
 550         public override void OnRelayout(Vector2 size, RelayoutContainer container)
 551         {
 552             base.OnRelayout(size, container);
 553
 554             wasRelayouted = true;
 555             if (needInitalizeLayouter) Init();
 556         }
 557
 558         /// <inheritdoc/>
 559         [EditorBrowsable(EditorBrowsableState.Never)]
 560         public override void NotifyDataSetChanged()
 561         {
 562             if (selectedItem != null)
 563             {
 564                 selectedItem = null;
 565             }
 566             if (selectedItems != null)
 567             {
 568                 selectedItems.Clear();
 569             }
 570
 571             base.NotifyDataSetChanged();
 572         }
 573
 574         /// <inheritdoc/>
 575         [EditorBrowsable(EditorBrowsableState.Never)]
 576         public override View GetNextFocusableView(View currentFocusedView, View.FocusDirection direction, bool loopEnabled)
 577         {
 578             View nextFocusedView = null;
 579
 580             if (focusedView == null)
 581             {
 582                 // If focusedView is null, find child which has previous data index
 583                 if (ContentContainer.Children.Count > 0 && InternalItemSource.Count > 0)
 584                 {
 585                     for (int i = 0; i < ContentContainer.Children.Count; i++)
 586                     {
 587                         RecyclerViewItem item = Children[i] as RecyclerViewItem;
 588                         if (item?.Index == prevFocusedDataIndex)
 589                         {
 590                             nextFocusedView = item;
 591                             break;
 592                         }
 593                     }
 594                 }
 595             }
 596             else
 597             {
 598                 // If this is not first focus, request next focus to Layouter
 599                 nextFocusedView = ItemsLayouter.RequestNextFocusableView(currentFocusedView, direction, loopEnabled);
 600             }
 601
 602             if (nextFocusedView != null)
 603             {
 604                 // Check next focused view is inside of visible area.
 605                 // If it is not, move scroll position to make it visible.
 606                 Position scrollPosition = ContentContainer.CurrentPosition;
 607                 float targetPosition = -(ScrollingDirection == Direction.Horizontal ? scrollPosition.X : scrollPosition.Y);
 608
 609                 float left = nextFocusedView.Position.X;
 610                 float right = nextFocusedView.Position.X + nextFocusedView.Size.Width;
 611                 float top = nextFocusedView.Position.Y;
 612                 float bottom = nextFocusedView.Position.Y + nextFocusedView.Size.Height;
 613
 614                 float visibleRectangleLeft = -scrollPosition.X;
 615                 float visibleRectangleRight = -scrollPosition.X + Size.Width;
 616                 float visibleRectangleTop = -scrollPosition.Y;
 617                 float visibleRectangleBottom = -scrollPosition.Y + Size.Height;
 618
 619                 if (ScrollingDirection == Direction.Horizontal)
 620                 {
 621                     if ((direction == View.FocusDirection.Left || direction == View.FocusDirection.Up) && left < visibleRectangleLeft)
 622                     {
 623                         targetPosition = left;
 624                     }
 625                     else if ((direction == View.FocusDirection.Right || direction == View.FocusDirection.Down) && right > visibleRectangleRight)
 626                     {
 627                         targetPosition = right - Size.Width;
 628                     }
 629                 }
 630                 else
 631                 {
 632                     if ((direction == View.FocusDirection.Up || direction == View.FocusDirection.Left) && top < visibleRectangleTop)
 633                     {
 634                         targetPosition = top;
 635                     }
 636                     else if ((direction == View.FocusDirection.Down || direction == View.FocusDirection.Right) && bottom > visibleRectangleBottom)
 637                     {
 638                         targetPosition = bottom - Size.Height;
 639                     }
 640                 }
 641
 642                 focusedView = nextFocusedView;
 643                 prevFocusedDataIndex = (nextFocusedView as RecyclerViewItem)?.Index ?? -1;
 644
 645                 ScrollTo(targetPosition, true);
 646             }
 647             else
 648             {
 649                 // If nextView is null, it means that we should move focus to outside of Control.
 650                 // Return FocusableView depending on direction.
 651                 switch (direction)
 652                 {
 653                     case View.FocusDirection.Left:
 654                         {
 655                             nextFocusedView = LeftFocusableView;
 656                             break;
 657                         }
 658                     case View.FocusDirection.Right:
 659                         {
 660                             nextFocusedView = RightFocusableView;
 661                             break;
 662                         }
 663                     case View.FocusDirection.Up:
 664                         {
 665                             nextFocusedView = UpFocusableView;
 666                             break;
 667                         }
 668                     case View.FocusDirection.Down:
 669                         {
 670                             nextFocusedView = DownFocusableView;
 671                             break;
 672                         }
 673                 }
 674
 675                 if (nextFocusedView != null)
 676                 {
 677                     focusedView = null;
 678                 }
 679                 else
 680                 {
 681                     //If FocusableView doesn't exist, not move focus.
 682                     nextFocusedView = focusedView;
 683                 }
 684             }
 685
 686             return nextFocusedView;
 687         }
 688
 689         /// <summary>
 690         /// Update selected items list in multiple selection.
 691         /// </summary>
 692         /// <param name="newSelection">updated selection list by user</param>
 693         /// <since_tizen> 9 </since_tizen>
 694         public void UpdateSelectedItems(IList<object> newSelection)
 695         {
 696             var oldSelection = new List<object>(SelectedItems);
 697
 698             suppressSelectionChangeNotification = true;
 699
 700             SelectedItems.Clear();
 701
 702             if (newSelection?.Count > 0)
 703             {
 704                 for (int n = 0; n < newSelection.Count; n++)
 705                 {
 706                     SelectedItems.Add(newSelection[n]);
 707                 }
 708             }
 709
 710             suppressSelectionChangeNotification = false;
 711
 712             SelectedItemsPropertyChanged(oldSelection, newSelection);
 713         }
 714
 715         /// <summary>
 716         /// Scroll to specific position with or without animation.
 717         /// </summary>
 718         /// <param name="position">Destination.</param>
 719         /// <param name="animate">Scroll with or without animation</param>
 720         /// <since_tizen> 9 </since_tizen>
 721         public new void ScrollTo(float position, bool animate)
 722         {
 723             if (ItemsLayouter == null) throw new Exception("Item Layouter must exist.");
 724             if ((InternalItemSource == null) || needInitalizeLayouter)
 725             {
 726                 delayedScrollTo = true;
 727                 delayedScrollToParam = (position, animate);
 728                 return;
 729             }
 730
 731             base.ScrollTo(position, animate);
 732         }
 733
 734         /// <summary>
 735         /// Scrolls to the item at the specified index.
 736         /// </summary>
 737         /// <param name="index">Index of item.</param>
 738         [EditorBrowsable(EditorBrowsableState.Never)]
 739         public new void ScrollToIndex(int index)
 740         {
 741             ScrollTo(index, true, ItemScrollTo.Start);
 742         }
 743
 744         /// <summary>
 745         /// Scroll to specific item's aligned position with or without animation.
 746         /// </summary>
 747         /// <param name="index">Target item index of dataset.</param>
 748         /// <param name="animate">Boolean flag of animation.</param>
 749         /// <param name="align">Align state of item. See details in <see cref="ItemScrollTo"/>.</param>
 750         /// <since_tizen> 9 </since_tizen>
 751         public virtual void ScrollTo(int index, bool animate = false, ItemScrollTo align = ItemScrollTo.Nearest)
 752         {
 753             if (ItemsLayouter == null) throw new Exception("Item Layouter must exist.");
 754             if ((InternalItemSource == null) || needInitalizeLayouter)
 755             {
 756                 delayedIndexScrollTo = true;
 757                 delayedIndexScrollToParam = (index, animate, align);
 758                 return;
 759             }
 760             if (index < 0 || index >= InternalItemSource.Count)
 761             {
 762                 throw new Exception("index is out of boundary. index should be a value between (0, " + InternalItemSource.Count.ToString() + ").");
 763             }
 764
 765             float scrollPos, curPos, curSize, curItemSize;
 766             (float x, float y) = ItemsLayouter.GetItemPosition(index);
 767             (float width, float height) = ItemsLayouter.GetItemSize(index);
 768             if (ScrollingDirection == Direction.Horizontal)
 769             {
 770                 scrollPos = x;
 771                 curPos = ScrollPosition.X;
 772                 curSize = Size.Width;
 773                 curItemSize = width;
 774             }
 775             else
 776             {
 777                 scrollPos = y;
 778                 curPos = ScrollPosition.Y;
 779                 curSize = Size.Height;
 780                 curItemSize = height;
 781             }
 782
 783             //Console.WriteLine("[NUI] ScrollTo [{0}:{1}], curPos{2}, itemPos{3}, curSize{4}, itemSize{5}", InternalItemSource.GetPosition(item), align, curPos, scrollPos, curSize, curItemSize);
 784             switch (align)
 785             {
 786                 case ItemScrollTo.Start:
 787                     //nothing necessary.
 788                     break;
 789                 case ItemScrollTo.Center:
 790                     scrollPos = scrollPos - (curSize / 2) + (curItemSize / 2);
 791                     break;
 792                 case ItemScrollTo.End:
 793                     scrollPos = scrollPos - curSize + curItemSize;
 794                     break;
 795                 case ItemScrollTo.Nearest:
 796                     if (scrollPos < curPos - curItemSize)
 797                     {
 798                         // item is placed before the current screen. scrollTo.Top
 799                     }
 800                     else if (scrollPos >= curPos + curSize + curItemSize)
 801                     {
 802                         // item is placed after the current screen. scrollTo.End
 803                         scrollPos = scrollPos - curSize + curItemSize;
 804                     }
 805                     else
 806                     {
 807                         // item is in the scroller. ScrollTo() is ignored.
 808                         return;
 809                     }
 810                     break;
 811             }
 812
 813             //Console.WriteLine("[NUI] ScrollTo [{0}]-------------------", scrollPos);
 814             base.ScrollTo(scrollPos, animate);
 815         }
 816
 817         /// <summary>
 818         /// Apply style to CollectionView
 819         /// </summary>
 820         /// <param name="viewStyle">The style to apply.</param>
 821         [EditorBrowsable(EditorBrowsableState.Never)]
 822         public override void ApplyStyle(ViewStyle viewStyle)
 823         {
 824             base.ApplyStyle(viewStyle);
 825             if (viewStyle != null)
 826             {
 827                 //Extension = RecyclerViewItemStyle.CreateExtension();
 828             }
 829             if (itemsLayouter != null)
 830             {
 831                 string styleName = "Tizen.NUI.Compoenents." + (itemsLayouter is LinearLayouter? "LinearLayouter" : (itemsLayouter is GridLayouter ? "GridLayouter" : "ItemsLayouter"));
 832                 ViewStyle layouterStyle = ThemeManager.GetStyle(styleName);
 833                 if (layouterStyle != null)
 834                     itemsLayouter.Padding = new Extents(layouterStyle.Padding);
 835             }
 836         }
 837
 838         // Realize and Decorate the item.
 839         internal override RecyclerViewItem RealizeItem(int index)
 840         {
 841             RecyclerViewItem item;
 842             if (index == 0 && Header != null)
 843             {
 844                 Header.Show();
 845                 return Header;
 846             }
 847
 848             if (index == InternalItemSource.Count - 1 && Footer != null)
 849             {
 850                 Footer.Show();
 851                 return Footer;
 852             }
 853
 854             if (isGrouped)
 855             {
 856                 var context = InternalItemSource.GetItem(index);
 857                 if (InternalItemSource.IsGroupHeader(index))
 858                 {
 859                     DataTemplate templ = (groupHeaderTemplate as DataTemplateSelector)?.SelectDataTemplate(context, this) ?? groupHeaderTemplate;
 860
 861                     RecyclerViewItem groupHeader = PopRecycleGroupCache(templ, true);
 862                     if (groupHeader == null)
 863                     {
 864                         groupHeader = (RecyclerViewItem)DataTemplateExtensions.CreateContent(groupHeaderTemplate, context, this);
 865
 866                         groupHeader.Template = templ;
 867                         groupHeader.isGroupHeader = true;
 868                         groupHeader.isGroupFooter = false;
 869                         ContentContainer.Add(groupHeader);
 870                     }
 871
 872                     if (groupHeader != null)
 873                     {
 874                         groupHeader.ParentItemsView = this;
 875                         groupHeader.Index = index;
 876                         groupHeader.ParentGroup = context;
 877                         groupHeader.BindingContext = context;
 878                     }
 879                     //group selection?
 880                     item = groupHeader;
 881                 }
 882                 else if (InternalItemSource.IsGroupFooter(index))
 883                 {
 884                     DataTemplate templ = (groupFooterTemplate as DataTemplateSelector)?.SelectDataTemplate(context, this) ?? groupFooterTemplate;
 885
 886                     RecyclerViewItem groupFooter = PopRecycleGroupCache(templ, false);
 887                     if (groupFooter == null)
 888                     {
 889                         groupFooter = (RecyclerViewItem)DataTemplateExtensions.CreateContent(groupFooterTemplate, context, this);
 890
 891                         groupFooter.Template = templ;
 892                         groupFooter.isGroupHeader = false;
 893                         groupFooter.isGroupFooter = true;
 894                         ContentContainer.Add(groupFooter);
 895                     }
 896
 897                     if (groupFooter != null)
 898                     {
 899                         groupFooter.ParentItemsView = this;
 900                         groupFooter.Index = index;
 901                         groupFooter.ParentGroup = context;
 902                         groupFooter.BindingContext = context;
 903                     }
 904                     //group selection?
 905                     item = groupFooter;
 906                 }
 907                 else
 908                 {
 909                     item = base.RealizeItem(index);
 910                     item.ParentGroup = InternalItemSource.GetGroupParent(index);
 911                 }
 912             }
 913             else
 914             {
 915                 item = base.RealizeItem(index);
 916             }
 917
 918             switch (SelectionMode)
 919             {
 920                 case ItemSelectionMode.Single:
 921                 case ItemSelectionMode.SingleAlways:
 922                     if (item.BindingContext != null && item.BindingContext == SelectedItem)
 923                     {
 924                         item.IsSelected = true;
 925                     }
 926                     break;
 927
 928                 case ItemSelectionMode.Multiple:
 929                     if ((item.BindingContext != null) && (SelectedItems?.Contains(item.BindingContext) ?? false))
 930                     {
 931                         item.IsSelected = true;
 932                     }
 933                     break;
 934                 case ItemSelectionMode.None:
 935                     item.IsSelectable = false;
 936                     break;
 937             }
 938             return item;
 939         }
 940
 941         // Unrealize and caching the item.
 942         internal override void UnrealizeItem(RecyclerViewItem item, bool recycle = true)
 943         {
 944             if (item == null) return;
 945             if (item == Header)
 946             {
 947                 item.Hide();
 948                 return;
 949             }
 950             if (item == Footer)
 951             {
 952                 item.Hide();
 953                 return;
 954             }
 955             if (item.isGroupHeader || item.isGroupFooter)
 956             {
 957                 item.Index = -1;
 958                 item.ParentItemsView = null;
 959                 item.BindingContext = null;
 960                 item.IsPressed = false;
 961                 item.IsSelected = false;
 962                 item.IsEnabled = true;
 963                 item.UpdateState();
 964                 //item.Relayout -= OnItemRelayout;
 965                 if (!recycle || !PushRecycleGroupCache(item))
 966                     Utility.Dispose(item);
 967                 return;
 968             }
 969
 970             base.UnrealizeItem(item, recycle);
 971         }
 972
 973         internal void SelectedItemsPropertyChanged(IList<object> oldSelection, IList<object> newSelection)
 974         {
 975             if (suppressSelectionChangeNotification)
 976             {
 977                 return;
 978             }
 979
 980             foreach (RecyclerViewItem item in ContentContainer.Children.Where((item) => item is RecyclerViewItem))
 981             {
 982                 if (item.BindingContext == null) continue;
 983                 if (newSelection.Contains(item.BindingContext))
 984                 {
 985                     if (!item.IsSelected) item.IsSelected = true;
 986                 }
 987                 else
 988                 {
 989                     if (item.IsSelected) item.IsSelected = false;
 990                 }
 991             }
 992             SelectionPropertyChanged(this, new SelectionChangedEventArgs(oldSelection, newSelection));
 993
 994             OnPropertyChanged(SelectedItemsProperty.PropertyName);
 995         }
 996
 997         /// <summary>
 998         /// Internal selection callback.
 999         /// </summary>
1000         /// <since_tizen> 9 </since_tizen>
1001         protected virtual void OnSelectionChanged(SelectionChangedEventArgs args)
1002         {
1003             //Selection Callback
1004         }
1005
1006         /// <summary>
1007         /// Adjust scrolling position by own scrolling rules.
1008         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1009         /// </summary>
1010         /// <param name="position">Scroll position which is calculated by ScrollableBase</param>
1011         /// <returns>Adjusted scroll destination</returns>
1012         [EditorBrowsable(EditorBrowsableState.Never)]
1013         protected override float AdjustTargetPositionOfScrollAnimation(float position)
1014         {
1015             // Destination is depending on implementation of layout manager.
1016             // Get destination from layout manager.
1017             return ItemsLayouter?.CalculateCandidateScrollPosition(position) ?? position;
1018         }
1019
1020         /// <inheritdoc/>
1021         [EditorBrowsable(EditorBrowsableState.Never)]
1022         protected override void ClearCache()
1023         {
1024             foreach (RecyclerViewItem item in recycleGroupHeaderCache)
1025             {
1026                 Utility.Dispose(item);
1027             }
1028             recycleGroupHeaderCache.Clear();
1029             foreach (RecyclerViewItem item in recycleGroupFooterCache)
1030             {
1031                 Utility.Dispose(item);
1032             }
1033             recycleGroupFooterCache.Clear();
1034             base.ClearCache();
1035         }
1036
1037
1038         /// <summary>
1039         /// OnScroll event callback. Requesting layout to the layouter with given scrollPosition.
1040         /// </summary>
1041         /// <param name="source">Scroll source object</param>
1042         /// <param name="args">Scroll event argument</param>
1043         /// <since_tizen> 9 </since_tizen>
1044         protected override void OnScrolling(object source, ScrollEventArgs args)
1045         {
1046             if (disposed) return;
1047
1048             if (needInitalizeLayouter && (ItemsLayouter != null))
1049             {
1050                 ItemsLayouter.Initialize(this);
1051                 needInitalizeLayouter = false;
1052             }
1053
1054             base.OnScrolling(source, args);
1055         }
1056
1057         /// <summary>
1058         /// Dispose ItemsView and all children on it.
1059         /// </summary>
1060         /// <param name="type">Dispose type.</param>
1061         /// <since_tizen> 9 </since_tizen>
1062         protected override void Dispose(DisposeTypes type)
1063         {
1064             if (disposed)
1065             {
1066                 return;
1067             }
1068
1069             if (type == DisposeTypes.Explicit)
1070             {
1071                 // From now on, no need to use this properties,
1072                 // so remove reference, to push it into garbage collector.
1073
1074                 // Arugable to disposing user-created members.
1075                 /*
1076                 if (Header != null)
1077                 {
1078                     Utility.Dispose(Header);
1079                     Header = null;
1080                 }
1081                 if (Footer != null)
1082                 {
1083                     Utility.Dispose(Footer);
1084                     Footer = null;
1085                 }
1086                 */
1087
1088                 groupHeaderTemplate = null;
1089                 groupFooterTemplate = null;
1090
1091                 if (selectedItem != null)
1092                 {
1093                     selectedItem = null;
1094                 }
1095                 if (selectedItems != null)
1096                 {
1097                     selectedItems.Clear();
1098                     selectedItems = null;
1099                 }
1100                 if (InternalItemSource != null)
1101                 {
1102                     InternalItemSource.Dispose();
1103                     InternalItemSource = null;
1104                 }
1105             }
1106
1107             base.Dispose(type);
1108         }
1109
1110         private static void SelectionPropertyChanged(CollectionView colView, SelectionChangedEventArgs args)
1111         {
1112             var command = colView.SelectionChangedCommand;
1113
1114             if (command != null)
1115             {
1116                 var commandParameter = colView.SelectionChangedCommandParameter;
1117
1118                 if (command.CanExecute(commandParameter))
1119                 {
1120                     command.Execute(commandParameter);
1121                 }
1122             }
1123             colView.SelectionChanged?.Invoke(colView, args);
1124             colView.OnSelectionChanged(args);
1125         }
1126
1127         private static object CoerceSelectedItems(BindableObject bindable, object value)
1128         {
1129             if (value == null)
1130             {
1131                 return new SelectionList((CollectionView)bindable);
1132             }
1133
1134             if (value is SelectionList)
1135             {
1136                 return value;
1137             }
1138
1139             return new SelectionList((CollectionView)bindable, value as IList<object>);
1140         }
1141
1142         private static void SelectionModePropertyChanged(BindableObject bindable, object oldValue, object newValue)
1143         {
1144             var colView = (CollectionView)bindable;
1145
1146             var oldMode = (ItemSelectionMode)oldValue;
1147             var newMode = (ItemSelectionMode)newValue;
1148
1149             IList<object> previousSelection = new List<object>();
1150             IList<object> newSelection = new List<object>();
1151
1152             switch (oldMode)
1153             {
1154                 case ItemSelectionMode.None:
1155                     break;
1156                 case ItemSelectionMode.Single:
1157                     if (colView.SelectedItem != null)
1158                     {
1159                         previousSelection.Add(colView.SelectedItem);
1160                     }
1161                     break;
1162                 case ItemSelectionMode.Multiple:
1163                     previousSelection = colView.SelectedItems;
1164                     break;
1165             }
1166
1167             switch (newMode)
1168             {
1169                 case ItemSelectionMode.None:
1170                     break;
1171                 case ItemSelectionMode.Single:
1172                     if (colView.SelectedItem != null)
1173                     {
1174                         newSelection.Add(colView.SelectedItem);
1175                     }
1176                     break;
1177                 case ItemSelectionMode.Multiple:
1178                     newSelection = colView.SelectedItems;
1179                     break;
1180             }
1181
1182             if (previousSelection.Count == newSelection.Count)
1183             {
1184                 if (previousSelection.Count == 0 || (previousSelection[0] == newSelection[0]))
1185                 {
1186                     // Both selections are empty or have the same single item; no reason to signal a change
1187                     return;
1188                 }
1189             }
1190
1191             var args = new SelectionChangedEventArgs(previousSelection, newSelection);
1192             SelectionPropertyChanged(colView, args);
1193         }
1194
1195         private void Init()
1196         {
1197             if (ItemsSource == null) return;
1198             if (ItemsLayouter == null) return;
1199             if (ItemTemplate == null) return;
1200
1201             if (disposed) return;
1202             if (needInitalizeLayouter)
1203             {
1204                 if (InternalItemSource == null) return;
1205
1206                 InternalItemSource.HasHeader = (header != null);
1207                 InternalItemSource.HasFooter = (footer != null);
1208             }
1209
1210             if (!wasRelayouted) return;
1211
1212             if (needInitalizeLayouter)
1213             {
1214                 itemsLayouter.Clear();
1215                 ClearCache();
1216
1217                 ItemsLayouter.Initialize(this);
1218                 needInitalizeLayouter = false;
1219             }
1220             ItemsLayouter.RequestLayout(0.0f, true);
1221
1222             if (delayedScrollTo)
1223             {
1224                 delayedScrollTo = false;
1225                 ScrollTo(delayedScrollToParam.position, delayedScrollToParam.anim);
1226             }
1227
1228             if (delayedIndexScrollTo)
1229             {
1230                 delayedIndexScrollTo = false;
1231                 ScrollTo(delayedIndexScrollToParam.index, delayedIndexScrollToParam.anim, delayedIndexScrollToParam.scrollTo);
1232             }
1233
1234             if (ScrollingDirection == Direction.Horizontal)
1235             {
1236                 ContentContainer.SizeWidth = ItemsLayouter.CalculateLayoutOrientationSize();
1237             }
1238             else
1239             {
1240                 ContentContainer.SizeHeight = ItemsLayouter.CalculateLayoutOrientationSize();
1241             }
1242         }
1243
1244         private bool PushRecycleGroupCache(RecyclerViewItem item)
1245         {
1246             if (item == null) throw new ArgumentNullException(nameof(item));
1247             if (RecycleCache.Count >= 20) return false;
1248             if (item.Template == null) return false;
1249             if (item.isGroupHeader)
1250             {
1251                 recycleGroupHeaderCache.Add(item);
1252             }
1253             else if (item.isGroupFooter)
1254             {
1255                 recycleGroupFooterCache.Add(item);
1256             }
1257             else return false;
1258             item.Hide();
1259             item.Index = -1;
1260             return true;
1261         }
1262
1263         private RecyclerViewItem PopRecycleGroupCache(DataTemplate Template, bool isHeader)
1264         {
1265             RecyclerViewItem viewItem = null;
1266
1267             var Cache = (isHeader ? recycleGroupHeaderCache : recycleGroupFooterCache);
1268             for (int i = 0; i < Cache.Count; i++)
1269             {
1270                 viewItem = Cache[i];
1271                 if (Template == viewItem.Template) break;
1272             }
1273
1274             if (viewItem != null)
1275             {
1276                 Cache.Remove(viewItem);
1277                 viewItem.Show();
1278             }
1279             return viewItem;
1280         }
1281         private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
1282         {
1283             switch (args.Action)
1284             {
1285                 case NotifyCollectionChangedAction.Add:
1286                     break;
1287                 case NotifyCollectionChangedAction.Remove:
1288                     // Clear removed items.
1289                     if (args.OldItems != null)
1290                     {
1291                         if (args.OldItems.Contains(selectedItem))
1292                         {
1293                             selectedItem = null;
1294                         }
1295
1296                         if (selectedItems != null)
1297                         {
1298                             foreach (object removed in args.OldItems)
1299                             {
1300                                 if (selectedItems.Contains(removed))
1301                                 {
1302                                     selectedItems.Remove(removed);
1303                                 }
1304                             }
1305                         }
1306                     }
1307                     break;
1308                 case NotifyCollectionChangedAction.Replace:
1309                     break;
1310                 case NotifyCollectionChangedAction.Move:
1311                     break;
1312                 case NotifyCollectionChangedAction.Reset:
1313                     break;
1314                 default:
1315                     throw new ArgumentOutOfRangeException(nameof(args));
1316             }
1317         }
1318
1319     }
1320 }