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 partial 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 GetValue(ItemTemplateProperty) as DataTemplate;
 274             }
 275             set
 276             {
 277                 SetValue(ItemTemplateProperty, value);
 278                 NotifyPropertyChanged();
 279             }
 280         }
 281         private DataTemplate InternalItemTemplate
 282         {
 283             get
 284             {
 285                 return itemTemplate;
 286             }
 287             set
 288             {
 289                 itemTemplate = value;
 290                 if (value == null)
 291                 {
 292                     return;
 293                 }
 294
 295                 needInitalizeLayouter = true;
 296                 Init();
 297             }
 298         }
 299
 300         /// <summary>
 301         /// Items Layouter.
 302         /// Layouting items on the scroll ContentContainer.
 303         /// <seealso cref="ItemsLayouter" />
 304         /// <seealso cref="LinearLayouter" />
 305         /// <seealso cref="GridLayouter" />
 306         /// </summary>
 307         /// <since_tizen> 9 </since_tizen>
 308         public virtual ItemsLayouter ItemsLayouter
 309         {
 310             get
 311             {
 312                 return GetValue(ItemsLayouterProperty) as ItemsLayouter;
 313             }
 314             set
 315             {
 316                 SetValue(ItemsLayouterProperty, value);
 317                 NotifyPropertyChanged();
 318             }
 319         }
 320         private ItemsLayouter InternalItemsLayouter
 321         {
 322             get
 323             {
 324                 return itemsLayouter;
 325             }
 326             set
 327             {
 328                 itemsLayouter?.Clear();
 329                 ClearCache();
 330
 331                 itemsLayouter = value;
 332                 base.InternalItemsLayouter = itemsLayouter;
 333                 if (value == null)
 334                 {
 335                     needInitalizeLayouter = false;
 336                     return;
 337                 }
 338
 339                 needInitalizeLayouter = true;
 340
 341                 var styleName = "Tizen.NUI.Components." + (itemsLayouter is LinearLayouter? "LinearLayouter" : (itemsLayouter is GridLayouter ? "GridLayouter" : "ItemsLayouter"));
 342                 ViewStyle layouterStyle = ThemeManager.GetStyle(styleName);
 343                 if (layouterStyle != null)
 344                 {
 345                     itemsLayouter.Padding = new Extents(layouterStyle.Padding);
 346                 }
 347                 Init();
 348             }
 349         }
 350
 351         /// <summary>
 352         /// Scrolling direction to display items layout.
 353         /// </summary>
 354         /// <since_tizen> 9 </since_tizen>
 355         public new Direction ScrollingDirection
 356         {
 357             get
 358             {
 359                 return (Direction)GetValue(ScrollingDirectionProperty);
 360             }
 361             set
 362             {
 363                 SetValue(ScrollingDirectionProperty, value);
 364                 NotifyPropertyChanged();
 365             }
 366         }
 367         private Direction InternalScrollingDirection
 368         {
 369             get
 370             {
 371                 return base.ScrollingDirection;
 372             }
 373             set
 374             {
 375                 if (base.ScrollingDirection != value)
 376                 {
 377                     base.ScrollingDirection = value;
 378                     needInitalizeLayouter = true;
 379                     Init();
 380                 }
 381             }
 382         }
 383
 384         /// <summary>
 385         /// Selected item in single selection.
 386         /// </summary>
 387         /// <since_tizen> 9 </since_tizen>
 388         public object SelectedItem
 389         {
 390             get => GetValue(SelectedItemProperty);
 391             set => SetValue(SelectedItemProperty, value);
 392         }
 393
 394         /// <summary>
 395         /// Selected items list in multiple selection.
 396         /// </summary>
 397         /// <since_tizen> 9 </since_tizen>
 398         public IList<object> SelectedItems
 399         {
 400             get => (IList<object>)GetValue(SelectedItemsProperty);
 401             // set => SetValue(SelectedItemsProperty, new SelectionList(this, value));
 402         }
 403
 404         /// <summary>
 405         /// Selection mode to handle items selection. See ItemSelectionMode for details.
 406         /// </summary>
 407         /// <since_tizen> 9 </since_tizen>
 408         public ItemSelectionMode SelectionMode
 409         {
 410             get => (ItemSelectionMode)GetValue(SelectionModeProperty);
 411             set => SetValue(SelectionModeProperty, value);
 412         }
 413
 414         /// <summary>
 415         /// Command of selection changed.
 416         /// </summary>
 417         [EditorBrowsable(EditorBrowsableState.Never)]
 418         public ICommand SelectionChangedCommand
 419         {
 420             get
 421             {
 422                 return GetValue(SelectionChangedCommandProperty) as ICommand;
 423             }
 424             set
 425             {
 426                 SetValue(SelectionChangedCommandProperty, value);
 427                 NotifyPropertyChanged();
 428             }
 429         }
 430         private ICommand InternalSelectionChangedCommand { set; get; }
 431
 432         /// <summary>
 433         /// Command parameter of selection changed.
 434         /// </summary>
 435         [EditorBrowsable(EditorBrowsableState.Never)]
 436         public object SelectionChangedCommandParameter
 437         {
 438             get
 439             {
 440                 return GetValue(SelectionChangedCommandParameterProperty);
 441             }
 442             set
 443             {
 444                 SetValue(SelectionChangedCommandParameterProperty, value);
 445                 NotifyPropertyChanged();
 446             }
 447         }
 448         private object InternalSelectionChangedCommandParameter { set; get; }
 449
 450         /// <summary>
 451         /// Header item placed in top-most position.
 452         /// </summary>
 453         /// <remarks>Please note that, internal index will be increased by header.</remarks>
 454         /// <since_tizen> 9 </since_tizen>
 455         public RecyclerViewItem Header
 456         {
 457             get
 458             {
 459                 return GetValue(HeaderProperty) as RecyclerViewItem;
 460             }
 461             set
 462             {
 463                 SetValue(HeaderProperty, value);
 464                 NotifyPropertyChanged();
 465             }
 466         }
 467         private RecyclerViewItem InternalHeader
 468         {
 469             get => header;
 470             set
 471             {
 472                 if (header != null)
 473                 {
 474                     //ContentContainer.Remove(header);
 475                     Utility.Dispose(header);
 476                 }
 477                 if (value != null)
 478                 {
 479                     value.Index = 0;
 480                     value.ParentItemsView = this;
 481                     value.IsHeader = true;
 482                     ContentContainer.Add(value);
 483                 }
 484                 header = value;
 485                 if (InternalItemSource != null)
 486                 {
 487                     InternalItemSource.HasHeader = (value != null);
 488                 }
 489                 needInitalizeLayouter = true;
 490                 Init();
 491             }
 492         }
 493
 494         /// <summary>
 495         /// Footer item placed in bottom-most position.
 496         /// </summary>
 497         /// <remarks>Please note that, internal index will be increased by footer.</remarks>
 498         /// <since_tizen> 9 </since_tizen>
 499         public RecyclerViewItem Footer
 500         {
 501             get
 502             {
 503                 return GetValue(FooterProperty) as RecyclerViewItem;
 504             }
 505             set
 506             {
 507                 SetValue(FooterProperty, value);
 508                 NotifyPropertyChanged();
 509             }
 510         }
 511         private RecyclerViewItem InternalFooter
 512         {
 513             get => footer;
 514             set
 515             {
 516                 if (footer != null)
 517                 {
 518                     //ContentContainer.Remove(footer);
 519                     Utility.Dispose(footer);
 520                 }
 521                 if (value != null)
 522                 {
 523                     value.Index = InternalItemSource?.Count ?? 0;
 524                     value.ParentItemsView = this;
 525                     value.IsFooter = true;
 526                     ContentContainer.Add(value);
 527                 }
 528                 footer = value;
 529                 if (InternalItemSource != null)
 530                 {
 531                     InternalItemSource.HasFooter = (value != null);
 532                 }
 533                 needInitalizeLayouter = true;
 534                 Init();
 535             }
 536         }
 537
 538         /// <summary>
 539         /// Enable groupable view.
 540         /// </summary>
 541         [EditorBrowsable(EditorBrowsableState.Never)]
 542         public bool IsGrouped
 543         {
 544             get
 545             {
 546                 return (bool)GetValue(IsGroupedProperty);
 547             }
 548             set
 549             {
 550                 SetValue(IsGroupedProperty, value);
 551                 NotifyPropertyChanged();
 552             }
 553         }
 554         private bool InternalIsGrouped
 555         {
 556             get => isGrouped;
 557             set
 558             {
 559                 isGrouped = value;
 560                 needInitalizeLayouter = true;
 561                 //Need to re-intialize Internal Item Source.
 562                 if (InternalItemSource != null)
 563                 {
 564                     InternalItemSource.Dispose();
 565                     InternalItemSource = null;
 566                 }
 567                 if (ItemsSource != null)
 568                     InternalItemSource = ItemsSourceFactory.Create(this);
 569                 Init();
 570             }
 571         }
 572
 573         /// <summary>
 574         ///  DataTemplate of group header.
 575         /// </summary>
 576         /// <remarks>Please note that, internal index will be increased by group header.
 577         /// GroupHeaderTemplate is essential for groupable view.</remarks>
 578         [EditorBrowsable(EditorBrowsableState.Never)]
 579         public DataTemplate GroupHeaderTemplate
 580         {
 581             get
 582             {
 583                 return GetValue(GroupHeaderTemplateProperty) as DataTemplate;
 584             }
 585             set
 586             {
 587                 SetValue(GroupHeaderTemplateProperty, value);
 588                 NotifyPropertyChanged();
 589             }
 590         }
 591         private DataTemplate InternalGroupHeaderTemplate
 592         {
 593             get
 594             {
 595                 return groupHeaderTemplate;
 596             }
 597             set
 598             {
 599                 groupHeaderTemplate = value;
 600                 needInitalizeLayouter = true;
 601                 //Need to re-intialize Internal Item Source.
 602                 if (InternalItemSource != null)
 603                 {
 604                     InternalItemSource.Dispose();
 605                     InternalItemSource = null;
 606                 }
 607                 if (ItemsSource != null)
 608                     InternalItemSource = ItemsSourceFactory.Create(this);
 609                 Init();
 610             }
 611         }
 612
 613         /// <summary>
 614         /// DataTemplate of group footer. Group feature is not supported yet.
 615         /// </summary>
 616         /// <remarks>Please note that, internal index will be increased by group footer.</remarks>
 617         [EditorBrowsable(EditorBrowsableState.Never)]
 618         public DataTemplate GroupFooterTemplate
 619         {
 620             get
 621             {
 622                 return GetValue(GroupFooterTemplateProperty) as DataTemplate;
 623             }
 624             set
 625             {
 626                 SetValue(GroupFooterTemplateProperty, value);
 627                 NotifyPropertyChanged();
 628             }
 629         }
 630         private DataTemplate InternalGroupFooterTemplate
 631         {
 632             get
 633             {
 634                 return groupFooterTemplate;
 635             }
 636             set
 637             {
 638                 groupFooterTemplate = value;
 639                 needInitalizeLayouter = true;
 640                 //Need to re-intialize Internal Item Source.
 641                 if (InternalItemSource != null)
 642                 {
 643                     InternalItemSource.Dispose();
 644                     InternalItemSource = null;
 645                 }
 646                 if (ItemsSource != null)
 647                     InternalItemSource = ItemsSourceFactory.Create(this);
 648                 Init();
 649             }
 650         }
 651
 652         /// <summary>
 653         /// Internal encapsulated items data source.
 654         /// </summary>
 655         internal new IGroupableItemSource InternalItemSource
 656         {
 657             get
 658             {
 659                 return (base.InternalItemSource as IGroupableItemSource);
 660             }
 661             set
 662             {
 663                 base.InternalItemSource = value;
 664             }
 665         }
 666
 667         /// <summary>
 668         /// Size strategy of measuring scroll content. see details in ItemSizingStrategy.
 669         /// </summary>
 670         [EditorBrowsable(EditorBrowsableState.Never)]
 671         internal ItemSizingStrategy SizingStrategy { get; set; }
 672
 673         /// <inheritdoc/>
 674         /// <since_tizen> 9 </since_tizen>
 675         public override void OnRelayout(Vector2 size, RelayoutContainer container)
 676         {
 677             base.OnRelayout(size, container);
 678
 679             wasRelayouted = true;
 680             if (needInitalizeLayouter) Init();
 681         }
 682
 683         /// <inheritdoc/>
 684         [EditorBrowsable(EditorBrowsableState.Never)]
 685         public override void NotifyDataSetChanged()
 686         {
 687             if (selectedItem != null)
 688             {
 689                 selectedItem = null;
 690             }
 691             if (selectedItems != null)
 692             {
 693                 selectedItems.Clear();
 694             }
 695
 696             base.NotifyDataSetChanged();
 697         }
 698
 699         /// <summary>
 700         /// Update selected items list in multiple selection.
 701         /// </summary>
 702         /// <param name="newSelection">updated selection list by user</param>
 703         /// <since_tizen> 9 </since_tizen>
 704         public void UpdateSelectedItems(IList<object> newSelection)
 705         {
 706             var oldSelection = new List<object>(SelectedItems);
 707
 708             suppressSelectionChangeNotification = true;
 709
 710             SelectedItems.Clear();
 711
 712             if (newSelection?.Count > 0)
 713             {
 714                 for (int n = 0; n < newSelection.Count; n++)
 715                 {
 716                     SelectedItems.Add(newSelection[n]);
 717                 }
 718             }
 719
 720             suppressSelectionChangeNotification = false;
 721
 722             SelectedItemsPropertyChanged(oldSelection, newSelection);
 723         }
 724
 725         /// <summary>
 726         /// Scroll to specific position with or without animation.
 727         /// </summary>
 728         /// <param name="position">Destination.</param>
 729         /// <param name="animate">Scroll with or without animation</param>
 730         /// <since_tizen> 9 </since_tizen>
 731         public new void ScrollTo(float position, bool animate)
 732         {
 733             if (ItemsLayouter == null) throw new Exception("Item Layouter must exist.");
 734             if ((InternalItemSource == null) || needInitalizeLayouter)
 735             {
 736                 delayedScrollTo = true;
 737                 delayedScrollToParam = (position, animate);
 738                 return;
 739             }
 740
 741             base.ScrollTo(position, animate);
 742         }
 743
 744         /// <summary>
 745         /// Scrolls to the item at the specified index.
 746         /// </summary>
 747         /// <param name="index">Index of item.</param>
 748         [EditorBrowsable(EditorBrowsableState.Never)]
 749         public new void ScrollToIndex(int index)
 750         {
 751             ScrollTo(index, true, ItemScrollTo.Start);
 752         }
 753
 754         /// <summary>
 755         /// Scroll to specific item's aligned position with or without animation.
 756         /// </summary>
 757         /// <param name="index">Target item index of dataset.</param>
 758         /// <param name="animate">Boolean flag of animation.</param>
 759         /// <param name="align">Align state of item. See details in <see cref="ItemScrollTo"/>.</param>
 760         /// <since_tizen> 9 </since_tizen>
 761         public virtual void ScrollTo(int index, bool animate = false, ItemScrollTo align = ItemScrollTo.Nearest)
 762         {
 763             if (ItemsLayouter == null) throw new Exception("Item Layouter must exist.");
 764             if ((InternalItemSource == null) || needInitalizeLayouter)
 765             {
 766                 delayedIndexScrollTo = true;
 767                 delayedIndexScrollToParam = (index, animate, align);
 768                 return;
 769             }
 770             if (index < 0 || index >= InternalItemSource.Count)
 771             {
 772                 throw new Exception("index is out of boundary. index should be a value between (0, " + InternalItemSource.Count.ToString() + ").");
 773             }
 774
 775             float scrollPos, curPos, curSize, curItemSize;
 776             (float x, float y) = ItemsLayouter.GetItemPosition(index);
 777             (float width, float height) = ItemsLayouter.GetItemSize(index);
 778             if (ScrollingDirection == Direction.Horizontal)
 779             {
 780                 scrollPos = x;
 781                 curPos = ScrollPosition.X;
 782                 curSize = Size.Width;
 783                 curItemSize = width;
 784             }
 785             else
 786             {
 787                 scrollPos = y;
 788                 curPos = ScrollPosition.Y;
 789                 curSize = Size.Height;
 790                 curItemSize = height;
 791             }
 792
 793             //Console.WriteLine("[NUI] ScrollTo [{0}:{1}], curPos{2}, itemPos{3}, curSize{4}, itemSize{5}", InternalItemSource.GetPosition(item), align, curPos, scrollPos, curSize, curItemSize);
 794             switch (align)
 795             {
 796                 case ItemScrollTo.Start:
 797                     //nothing necessary.
 798                     break;
 799                 case ItemScrollTo.Center:
 800                     scrollPos = scrollPos - (curSize / 2) + (curItemSize / 2);
 801                     break;
 802                 case ItemScrollTo.End:
 803                     scrollPos = scrollPos - curSize + curItemSize;
 804                     break;
 805                 case ItemScrollTo.Nearest:
 806                     if (scrollPos < curPos - curItemSize)
 807                     {
 808                         // item is placed before the current screen. scrollTo.Top
 809                     }
 810                     else if (scrollPos >= curPos + curSize + curItemSize)
 811                     {
 812                         // item is placed after the current screen. scrollTo.End
 813                         scrollPos = scrollPos - curSize + curItemSize;
 814                     }
 815                     else
 816                     {
 817                         // item is in the scroller. ScrollTo() is ignored.
 818                         return;
 819                     }
 820                     break;
 821             }
 822
 823             //Console.WriteLine("[NUI] ScrollTo [{0}]-------------------", scrollPos);
 824             base.ScrollTo(scrollPos, animate);
 825         }
 826
 827         /// <summary>
 828         /// Apply style to CollectionView
 829         /// </summary>
 830         /// <param name="viewStyle">The style to apply.</param>
 831         [EditorBrowsable(EditorBrowsableState.Never)]
 832         public override void ApplyStyle(ViewStyle viewStyle)
 833         {
 834             base.ApplyStyle(viewStyle);
 835             if (viewStyle != null)
 836             {
 837                 //Extension = RecyclerViewItemStyle.CreateExtension();
 838             }
 839             if (itemsLayouter != null)
 840             {
 841                 string styleName = "Tizen.NUI.Compoenents." + (itemsLayouter is LinearLayouter? "LinearLayouter" : (itemsLayouter is GridLayouter ? "GridLayouter" : "ItemsLayouter"));
 842                 ViewStyle layouterStyle = ThemeManager.GetStyle(styleName);
 843                 if (layouterStyle != null)
 844                     itemsLayouter.Padding = new Extents(layouterStyle.Padding);
 845             }
 846         }
 847
 848         /// <summary>
 849         /// Initialize AT-SPI object.
 850         /// </summary>
 851         [EditorBrowsable(EditorBrowsableState.Never)]
 852         public override void OnInitialize()
 853         {
 854             base.OnInitialize();
 855             SetAccessibilityConstructor(Role.List);
 856         }
 857
 858         /// <summary>
 859         /// Scroll to specified item
 860         /// </summary>
 861         /// <remarks>
 862         /// Make sure that the item that is about to receive the accessibility highlight is visible.
 863         /// </remarks>
 864         [EditorBrowsable(EditorBrowsableState.Never)]
 865         protected override bool AccessibilityScrollToChild(View child)
 866         {
 867             if (ScrollingDirection == Direction.Horizontal)
 868             {
 869                 if (child.ScreenPosition.X + child.Size.Width <= this.ScreenPosition.X)
 870                 {
 871                     ScrollTo((float)(child.ScreenPosition.X - ContentContainer.ScreenPosition.X), false);
 872                 }
 873                 else if (child.ScreenPosition.X >= this.ScreenPosition.X + this.Size.Width)
 874                 {
 875                     ScrollTo((float)(child.ScreenPosition.X + child.Size.Width - ContentContainer.ScreenPosition.X - this.Size.Width), false);
 876                 }
 877             }
 878             else
 879             {
 880                 if (child.ScreenPosition.Y + child.Size.Height <= this.ScreenPosition.Y)
 881                 {
 882                     ScrollTo((float)(child.ScreenPosition.Y - ContentContainer.ScreenPosition.Y), false);
 883                 }
 884                 else if (child.ScreenPosition.Y >= this.ScreenPosition.Y + this.Size.Height)
 885                 {
 886                     ScrollTo((float)(child.ScreenPosition.Y + child.Size.Height - ContentContainer.ScreenPosition.Y - this.Size.Height), false);
 887                 }
 888             }
 889             return true;
 890         }
 891
 892         // Realize and Decorate the item.
 893         internal override RecyclerViewItem RealizeItem(int index)
 894         {
 895             RecyclerViewItem item;
 896             if (index == 0 && Header != null)
 897             {
 898                 Header.Show();
 899                 return Header;
 900             }
 901
 902             if (index == InternalItemSource.Count - 1 && Footer != null)
 903             {
 904                 Footer.Show();
 905                 return Footer;
 906             }
 907
 908             if (isGrouped)
 909             {
 910                 var context = InternalItemSource.GetItem(index);
 911                 if (InternalItemSource.IsGroupHeader(index))
 912                 {
 913                     DataTemplate templ = (groupHeaderTemplate as DataTemplateSelector)?.SelectDataTemplate(context, this) ?? groupHeaderTemplate;
 914
 915                     RecyclerViewItem groupHeader = PopRecycleGroupCache(templ, true);
 916                     if (groupHeader == null)
 917                     {
 918                         groupHeader = (RecyclerViewItem)DataTemplateExtensions.CreateContent(groupHeaderTemplate, context, this);
 919
 920                         groupHeader.Template = templ;
 921                         groupHeader.isGroupHeader = true;
 922                         groupHeader.isGroupFooter = false;
 923                         ContentContainer.Add(groupHeader);
 924                     }
 925
 926                     if (groupHeader != null)
 927                     {
 928                         groupHeader.ParentItemsView = this;
 929                         groupHeader.Index = index;
 930                         groupHeader.ParentGroup = context;
 931                         groupHeader.BindingContext = context;
 932                     }
 933                     //group selection?
 934                     item = groupHeader;
 935                 }
 936                 else if (InternalItemSource.IsGroupFooter(index))
 937                 {
 938                     DataTemplate templ = (groupFooterTemplate as DataTemplateSelector)?.SelectDataTemplate(context, this) ?? groupFooterTemplate;
 939
 940                     RecyclerViewItem groupFooter = PopRecycleGroupCache(templ, false);
 941                     if (groupFooter == null)
 942                     {
 943                         groupFooter = (RecyclerViewItem)DataTemplateExtensions.CreateContent(groupFooterTemplate, context, this);
 944
 945                         groupFooter.Template = templ;
 946                         groupFooter.isGroupHeader = false;
 947                         groupFooter.isGroupFooter = true;
 948                         ContentContainer.Add(groupFooter);
 949                     }
 950
 951                     if (groupFooter != null)
 952                     {
 953                         groupFooter.ParentItemsView = this;
 954                         groupFooter.Index = index;
 955                         groupFooter.ParentGroup = context;
 956                         groupFooter.BindingContext = context;
 957                     }
 958                     //group selection?
 959                     item = groupFooter;
 960                 }
 961                 else
 962                 {
 963                     item = base.RealizeItem(index);
 964                     if (item == null)
 965                         throw new Exception("Item realize failed by Null content return.");
 966                     item.ParentGroup = InternalItemSource.GetGroupParent(index);
 967                 }
 968             }
 969             else
 970             {
 971                 item = base.RealizeItem(index);
 972             }
 973
 974             if (item == null)
 975                 throw new Exception("Item realize failed by Null content return.");
 976
 977             switch (SelectionMode)
 978             {
 979                 case ItemSelectionMode.Single:
 980                 case ItemSelectionMode.SingleAlways:
 981                     if (item.BindingContext != null && item.BindingContext == SelectedItem)
 982                     {
 983                         item.IsSelected = true;
 984                     }
 985                     break;
 986
 987                 case ItemSelectionMode.Multiple:
 988                     if ((item.BindingContext != null) && (SelectedItems?.Contains(item.BindingContext) ?? false))
 989                     {
 990                         item.IsSelected = true;
 991                     }
 992                     break;
 993                 case ItemSelectionMode.None:
 994                     item.IsSelectable = false;
 995                     break;
 996             }
 997             return item;
 998         }
 999
1000         // Unrealize and caching the item.
1001         internal override void UnrealizeItem(RecyclerViewItem item, bool recycle = true)
1002         {
1003             if (item == null) return;
1004             if (item == Header)
1005             {
1006                 item?.Hide();
1007                 return;
1008             }
1009             if (item == Footer)
1010             {
1011                 item.Hide();
1012                 return;
1013             }
1014             if (item.isGroupHeader || item.isGroupFooter)
1015             {
1016                 item.Index = -1;
1017                 item.ParentItemsView = null;
1018                 item.BindingContext = null;
1019                 item.IsPressed = false;
1020                 item.IsSelected = false;
1021                 item.IsEnabled = true;
1022                 item.UpdateState();
1023                 //item.Relayout -= OnItemRelayout;
1024                 if (!recycle || !PushRecycleGroupCache(item))
1025                     Utility.Dispose(item);
1026                 return;
1027             }
1028
1029             base.UnrealizeItem(item, recycle);
1030         }
1031
1032         internal void SelectedItemsPropertyChanged(IList<object> oldSelection, IList<object> newSelection)
1033         {
1034             if (suppressSelectionChangeNotification)
1035             {
1036                 return;
1037             }
1038
1039             foreach (RecyclerViewItem item in ContentContainer.Children.Where((item) => item is RecyclerViewItem))
1040             {
1041                 if (item.BindingContext == null) continue;
1042                 if (newSelection.Contains(item.BindingContext))
1043                 {
1044                     if (!item.IsSelected) item.IsSelected = true;
1045                 }
1046                 else
1047                 {
1048                     if (item.IsSelected) item.IsSelected = false;
1049                 }
1050             }
1051             SelectionPropertyChanged(this, new SelectionChangedEventArgs(oldSelection, newSelection));
1052
1053             OnPropertyChanged(SelectedItemsProperty.PropertyName);
1054         }
1055
1056         /// <summary>
1057         /// Internal selection callback.
1058         /// </summary>
1059         /// <since_tizen> 9 </since_tizen>
1060         protected virtual void OnSelectionChanged(SelectionChangedEventArgs args)
1061         {
1062             //Selection Callback
1063         }
1064
1065         /// <summary>
1066         /// Adjust scrolling position by own scrolling rules.
1067         /// Override this function when developer wants to change destination of flicking.(e.g. always snap to center of item)
1068         /// </summary>
1069         /// <param name="position">Scroll position which is calculated by ScrollableBase</param>
1070         /// <returns>Adjusted scroll destination</returns>
1071         [EditorBrowsable(EditorBrowsableState.Never)]
1072         protected override float AdjustTargetPositionOfScrollAnimation(float position)
1073         {
1074             // Destination is depending on implementation of layout manager.
1075             // Get destination from layout manager.
1076             return ItemsLayouter?.CalculateCandidateScrollPosition(position) ?? position;
1077         }
1078
1079         /// <inheritdoc/>
1080         [EditorBrowsable(EditorBrowsableState.Never)]
1081         protected override void ClearCache()
1082         {
1083             foreach (RecyclerViewItem item in recycleGroupHeaderCache)
1084             {
1085                 Utility.Dispose(item);
1086             }
1087             recycleGroupHeaderCache.Clear();
1088             foreach (RecyclerViewItem item in recycleGroupFooterCache)
1089             {
1090                 Utility.Dispose(item);
1091             }
1092             recycleGroupFooterCache.Clear();
1093             base.ClearCache();
1094         }
1095
1096
1097         /// <summary>
1098         /// OnScroll event callback. Requesting layout to the layouter with given scrollPosition.
1099         /// </summary>
1100         /// <param name="source">Scroll source object</param>
1101         /// <param name="args">Scroll event argument</param>
1102         /// <since_tizen> 9 </since_tizen>
1103         protected override void OnScrolling(object source, ScrollEventArgs args)
1104         {
1105             if (disposed) return;
1106
1107             if (needInitalizeLayouter && (ItemsLayouter != null))
1108             {
1109                 ItemsLayouter.Initialize(this);
1110                 needInitalizeLayouter = false;
1111             }
1112
1113             base.OnScrolling(source, args);
1114         }
1115
1116         /// <summary>
1117         /// Dispose ItemsView and all children on it.
1118         /// </summary>
1119         /// <param name="type">Dispose type.</param>
1120         /// <since_tizen> 9 </since_tizen>
1121         protected override void Dispose(DisposeTypes type)
1122         {
1123             if (disposed)
1124             {
1125                 return;
1126             }
1127
1128             if (type == DisposeTypes.Explicit)
1129             {
1130                 // From now on, no need to use this properties,
1131                 // so remove reference, to push it into garbage collector.
1132
1133                 // Arugable to disposing user-created members.
1134                 /*
1135                 if (Header != null)
1136                 {
1137                     Utility.Dispose(Header);
1138                     Header = null;
1139                 }
1140                 if (Footer != null)
1141                 {
1142                     Utility.Dispose(Footer);
1143                     Footer = null;
1144                 }
1145                 */
1146
1147                 groupHeaderTemplate = null;
1148                 groupFooterTemplate = null;
1149
1150                 if (selectedItem != null)
1151                 {
1152                     selectedItem = null;
1153                 }
1154                 if (selectedItems != null)
1155                 {
1156                     selectedItems.Clear();
1157                     selectedItems = null;
1158                 }
1159                 if (InternalItemSource != null)
1160                 {
1161                     InternalItemSource.Dispose();
1162                     InternalItemSource = null;
1163                 }
1164             }
1165
1166             base.Dispose(type);
1167         }
1168
1169         private static void SelectionPropertyChanged(CollectionView colView, SelectionChangedEventArgs args)
1170         {
1171             var command = colView.SelectionChangedCommand;
1172
1173             if (command != null)
1174             {
1175                 var commandParameter = colView.SelectionChangedCommandParameter;
1176
1177                 if (command.CanExecute(commandParameter))
1178                 {
1179                     command.Execute(commandParameter);
1180                 }
1181             }
1182             colView.SelectionChanged?.Invoke(colView, args);
1183             colView.OnSelectionChanged(args);
1184         }
1185
1186         private static object CoerceSelectedItems(BindableObject bindable, object value)
1187         {
1188             if (value == null)
1189             {
1190                 return new SelectionList((CollectionView)bindable);
1191             }
1192
1193             if (value is SelectionList)
1194             {
1195                 return value;
1196             }
1197
1198             return new SelectionList((CollectionView)bindable, value as IList<object>);
1199         }
1200
1201         private static void SelectionModePropertyChanged(BindableObject bindable, object oldValue, object newValue)
1202         {
1203             var colView = (CollectionView)bindable;
1204
1205             var oldMode = (ItemSelectionMode)oldValue;
1206             var newMode = (ItemSelectionMode)newValue;
1207
1208             IList<object> previousSelection = new List<object>();
1209             IList<object> newSelection = new List<object>();
1210
1211             switch (oldMode)
1212             {
1213                 case ItemSelectionMode.None:
1214                     break;
1215                 case ItemSelectionMode.Single:
1216                     if (colView.SelectedItem != null)
1217                     {
1218                         previousSelection.Add(colView.SelectedItem);
1219                     }
1220                     break;
1221                 case ItemSelectionMode.Multiple:
1222                     previousSelection = colView.SelectedItems;
1223                     break;
1224             }
1225
1226             switch (newMode)
1227             {
1228                 case ItemSelectionMode.None:
1229                     break;
1230                 case ItemSelectionMode.Single:
1231                     if (colView.SelectedItem != null)
1232                     {
1233                         newSelection.Add(colView.SelectedItem);
1234                     }
1235                     break;
1236                 case ItemSelectionMode.Multiple:
1237                     newSelection = colView.SelectedItems;
1238                     break;
1239             }
1240
1241             if (previousSelection.Count == newSelection.Count)
1242             {
1243                 if (previousSelection.Count == 0 || (previousSelection[0] == newSelection[0]))
1244                 {
1245                     // Both selections are empty or have the same single item; no reason to signal a change
1246                     return;
1247                 }
1248             }
1249
1250             var args = new SelectionChangedEventArgs(previousSelection, newSelection);
1251             SelectionPropertyChanged(colView, args);
1252         }
1253
1254         private void Init()
1255         {
1256             if (ItemsSource == null) return;
1257             if (ItemsLayouter == null) return;
1258             if (ItemTemplate == null) return;
1259
1260             if (disposed) return;
1261             if (needInitalizeLayouter)
1262             {
1263                 if (InternalItemSource == null) return;
1264
1265                 InternalItemSource.HasHeader = (header != null);
1266                 InternalItemSource.HasFooter = (footer != null);
1267             }
1268
1269             if (!wasRelayouted) return;
1270
1271             if (needInitalizeLayouter)
1272             {
1273                 itemsLayouter.Clear();
1274                 ClearCache();
1275
1276                 ItemsLayouter.Initialize(this);
1277                 needInitalizeLayouter = false;
1278             }
1279             ItemsLayouter.RequestLayout(0.0f, true);
1280
1281             if (delayedScrollTo)
1282             {
1283                 delayedScrollTo = false;
1284                 ScrollTo(delayedScrollToParam.position, delayedScrollToParam.anim);
1285             }
1286
1287             if (delayedIndexScrollTo)
1288             {
1289                 delayedIndexScrollTo = false;
1290                 ScrollTo(delayedIndexScrollToParam.index, delayedIndexScrollToParam.anim, delayedIndexScrollToParam.scrollTo);
1291             }
1292
1293             if (ScrollingDirection == Direction.Horizontal)
1294             {
1295                 ContentContainer.SizeWidth = ItemsLayouter.CalculateLayoutOrientationSize();
1296             }
1297             else
1298             {
1299                 ContentContainer.SizeHeight = ItemsLayouter.CalculateLayoutOrientationSize();
1300             }
1301         }
1302
1303         private bool PushRecycleGroupCache(RecyclerViewItem item)
1304         {
1305             if (item == null) throw new ArgumentNullException(nameof(item));
1306             if (RecycleCache.Count >= 20) return false;
1307             if (item.Template == null) return false;
1308             if (item.isGroupHeader)
1309             {
1310                 recycleGroupHeaderCache.Add(item);
1311             }
1312             else if (item.isGroupFooter)
1313             {
1314                 recycleGroupFooterCache.Add(item);
1315             }
1316             else return false;
1317             item.Hide();
1318             item.Index = -1;
1319             return true;
1320         }
1321
1322         private RecyclerViewItem PopRecycleGroupCache(DataTemplate Template, bool isHeader)
1323         {
1324             RecyclerViewItem viewItem = null;
1325
1326             var Cache = (isHeader ? recycleGroupHeaderCache : recycleGroupFooterCache);
1327             for (int i = 0; i < Cache.Count; i++)
1328             {
1329                 viewItem = Cache[i];
1330                 if (Template == viewItem.Template) break;
1331             }
1332
1333             if (viewItem != null)
1334             {
1335                 Cache.Remove(viewItem);
1336                 viewItem.Show();
1337             }
1338             return viewItem;
1339         }
1340         private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
1341         {
1342             switch (args.Action)
1343             {
1344                 case NotifyCollectionChangedAction.Add:
1345                     break;
1346                 case NotifyCollectionChangedAction.Remove:
1347                     // Clear removed items.
1348                     if (args.OldItems != null)
1349                     {
1350                         if (args.OldItems.Contains(selectedItem))
1351                         {
1352                             selectedItem = null;
1353                         }
1354
1355                         if (selectedItems != null)
1356                         {
1357                             foreach (object removed in args.OldItems)
1358                             {
1359                                 if (selectedItems.Contains(removed))
1360                                 {
1361                                     selectedItems.Remove(removed);
1362                                 }
1363                             }
1364                         }
1365                     }
1366                     break;
1367                 case NotifyCollectionChangedAction.Replace:
1368                     break;
1369                 case NotifyCollectionChangedAction.Move:
1370                     break;
1371                 case NotifyCollectionChangedAction.Reset:
1372                     break;
1373                 default:
1374                     throw new ArgumentOutOfRangeException(nameof(args));
1375             }
1376         }
1377
1378     }
1379 }