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@@ -2,37 +2,62 @@
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using System.Collections;
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using System.Collections.Generic;
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using System.Collections.Specialized;
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-using System.Linq;
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-using Avalonia.Controls.Utils;
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namespace Avalonia.Controls.Selection
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{
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- public abstract class SelectionNodeBase<T> : ICollectionChangedListener
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+ /// <summary>
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+ /// Base class for selection models.
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+ /// </summary>
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+ /// <typeparam name="T">The type of the element being selected.</typeparam>
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+ public abstract class SelectionNodeBase<T>
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{
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private IEnumerable? _source;
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private bool _rangesEnabled;
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private List<IndexRange>? _ranges;
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- private int _collectionChanging;
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+ /// <summary>
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+ /// Gets or sets the source collection.
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+ /// </summary>
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protected IEnumerable? Source
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{
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get => _source;
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set
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{
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+ void OnPreChanged(object? sender, NotifyCollectionChangedEventArgs e) => OnSourceCollectionChangeStarted();
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+ void OnChanged(object? sender, NotifyCollectionChangedEventArgs e) => OnSourceCollectionChanged(e);
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+ void OnPostChanged(object? sender, NotifyCollectionChangedEventArgs e) => OnSourceCollectionChangeFinished();
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+
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if (_source != value)
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{
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- if (ItemsView?.Inner is INotifyCollectionChanged inccOld)
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- CollectionChangedEventManager.Instance.RemoveListener(inccOld, this);
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+ if (ItemsView is not null)
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+ {
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+ ItemsView.PreCollectionChanged -= OnPreChanged;
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+ ItemsView.CollectionChanged -= OnChanged;
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+ ItemsView.PostCollectionChanged -= OnPostChanged;
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+ }
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+
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_source = value;
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- ItemsView = value is object ? ItemsSourceView.GetOrCreate<T>(value) : null;
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- if (ItemsView?.Inner is INotifyCollectionChanged inccNew)
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- CollectionChangedEventManager.Instance.AddListener(inccNew, this);
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+ ItemsView = value is not null ? ItemsSourceView.GetOrCreate<T>(value) : null;
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+
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+ if (ItemsView is not null)
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+ {
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+ ItemsView.PreCollectionChanged += OnPreChanged;
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+ ItemsView.CollectionChanged += OnChanged;
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+ ItemsView.PostCollectionChanged += OnPostChanged;
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+ }
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}
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}
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}
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- protected bool IsSourceCollectionChanging => _collectionChanging > 0;
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+ /// <summary>
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+ /// Gets an <see cref="ItemsSourceView{T}"/> of the <see cref="Source"/>.
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+ /// </summary>
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+ protected internal ItemsSourceView<T>? ItemsView { get; set; }
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+ /// <summary>
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+ /// Gets or sets a value indicating whether range selection is currently enabled for
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+ /// the selection node.
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+ /// </summary>
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protected bool RangesEnabled
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{
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get => _rangesEnabled;
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@@ -50,8 +75,6 @@ namespace Avalonia.Controls.Selection
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}
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}
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- internal ItemsSourceView<T>? ItemsView { get; set; }
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-
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internal IReadOnlyList<IndexRange> Ranges
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{
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get
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@@ -65,81 +88,170 @@ namespace Avalonia.Controls.Selection
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}
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}
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- void ICollectionChangedListener.PreChanged(INotifyCollectionChanged sender, NotifyCollectionChangedEventArgs e)
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+ /// <summary>
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+ /// Called when the source collection starts changing.
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+ /// </summary>
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+ protected virtual void OnSourceCollectionChangeStarted()
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{
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- ++_collectionChanging;
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}
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- void ICollectionChangedListener.Changed(INotifyCollectionChanged sender, NotifyCollectionChangedEventArgs e)
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+ /// <summary>
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+ /// Called when the <see cref="Source"/> collection changes.
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+ /// </summary>
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+ /// <param name="e">The details of the collection change.</param>
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+ /// <remarks>
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+ /// The implementation in <see cref="SelectionNodeBase{T}"/> calls
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+ /// <see cref="OnItemsAdded(int, IList)"/> and <see cref="OnItemsRemoved(int, IList)"/>
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+ /// in order to calculate how the collection change affects the currently selected items.
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+ /// It then calls <see cref="OnIndexesChanged(int, int)"/> and
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+ /// <see cref="OnSelectionRemoved(int, int, IReadOnlyList{T})"/> if necessary, according
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+ /// to the <see cref="CollectionChangeState"/> returned by those methods.
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+ ///
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+ /// Override this method and <see cref="OnSourceCollectionChangeFinished"/> to provide
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+ /// custom handling of source collection changes.
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+ /// </remarks>
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+ protected virtual void OnSourceCollectionChanged(NotifyCollectionChangedEventArgs e)
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{
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- OnSourceCollectionChanged(e);
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- }
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+ var shiftDelta = 0;
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+ var shiftIndex = -1;
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+ List<T>? removed = null;
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- void ICollectionChangedListener.PostChanged(INotifyCollectionChanged sender, NotifyCollectionChangedEventArgs e)
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- {
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- if (--_collectionChanging == 0)
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+ if (!IsValidCollectionChange(e))
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{
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- OnSourceCollectionChangeFinished();
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+ return;
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}
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- }
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-
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- protected abstract void OnSourceCollectionChangeFinished();
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-
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- private protected abstract void OnIndexesChanged(int shiftIndex, int shiftDelta);
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-
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- private protected abstract void OnSourceReset();
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- private protected abstract void OnSelectionChanged(IReadOnlyList<T> deselectedItems);
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-
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- private protected int CommitSelect(IndexRange range)
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- {
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- if (RangesEnabled)
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+ switch (e.Action)
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{
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- _ranges ??= new List<IndexRange>();
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- return IndexRange.Add(_ranges, range);
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+ case NotifyCollectionChangedAction.Add:
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+ {
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+ var change = OnItemsAdded(e.NewStartingIndex, e.NewItems!);
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+ shiftIndex = change.ShiftIndex;
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+ shiftDelta = change.ShiftDelta;
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+ break;
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+ }
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+ case NotifyCollectionChangedAction.Remove:
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+ {
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+ var change = OnItemsRemoved(e.OldStartingIndex, e.OldItems!);
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+ shiftIndex = change.ShiftIndex;
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+ shiftDelta = change.ShiftDelta;
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+ removed = change.RemovedItems;
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+ break;
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+ }
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+ case NotifyCollectionChangedAction.Replace:
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+ case NotifyCollectionChangedAction.Move:
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+ {
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+ var removeChange = OnItemsRemoved(e.OldStartingIndex, e.OldItems!);
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+ var addChange = OnItemsAdded(e.NewStartingIndex, e.NewItems!);
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+ shiftIndex = removeChange.ShiftIndex;
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+ shiftDelta = removeChange.ShiftDelta + addChange.ShiftDelta;
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+ removed = removeChange.RemovedItems;
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+ }
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+ break;
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+ case NotifyCollectionChangedAction.Reset:
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+ OnSourceReset();
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+ break;
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}
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- return 0;
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+ if (shiftDelta != 0)
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+ OnIndexesChanged(shiftIndex, shiftDelta);
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+ if (removed is not null)
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+ OnSelectionRemoved(shiftIndex, -shiftDelta, removed);
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}
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- private protected int CommitSelect(IReadOnlyList<IndexRange> ranges)
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+ /// <summary>
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+ /// Called when the source collection has finished changing, and all CollectionChanged
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+ /// handlers have run.
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+ /// </summary>
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+ /// <remarks>
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+ /// Override this method to respond to the end of a collection change instead of acting at
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+ /// the end of <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>
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+ /// in order to ensure that all UI subscribers to the source collection change event have
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+ /// had chance to run.
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+ /// </remarks>
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+ protected virtual void OnSourceCollectionChangeFinished()
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{
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- if (RangesEnabled)
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- {
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- _ranges ??= new List<IndexRange>();
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- return IndexRange.Add(_ranges, ranges);
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- }
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+ }
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- return 0;
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+ /// <summary>
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+ /// Called by <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>,
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+ /// detailing the indexes changed by the collection changing.
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+ /// </summary>
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+ /// <param name="shiftIndex">The first index that was shifted.</param>
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+ /// <param name="shiftDelta">
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+ /// If positive, the number of items inserted, or if negative the number of items removed.
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+ /// </param>
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+ protected virtual void OnIndexesChanged(int shiftIndex, int shiftDelta)
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+ {
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+ }
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+
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+ /// <summary>
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+ /// Called by <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>,
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+ /// on collection reset.
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+ /// </summary>
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+ protected abstract void OnSourceReset();
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+
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+ /// <summary>
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+ /// Called by <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>,
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+ /// detailing the items removed by a collection change.
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+ /// </summary>
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+ protected virtual void OnSelectionRemoved(int index, int count, IReadOnlyList<T> deselectedItems)
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+ {
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}
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- private protected int CommitDeselect(IndexRange range)
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+ /// <summary>
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+ /// If <see cref="RangesEnabled"/>, adds the specified range to the selection.
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+ /// </summary>
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+ /// <param name="begin">The inclusive index of the start of the range to select.</param>
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+ /// <param name="end">The inclusive index of the end of the range to select.</param>
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+ /// <returns>The number of items selected.</returns>
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+ protected int CommitSelect(int begin, int end)
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{
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if (RangesEnabled)
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{
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_ranges ??= new List<IndexRange>();
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- return IndexRange.Remove(_ranges, range);
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+ return IndexRange.Add(_ranges, new IndexRange(begin, end));
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}
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return 0;
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}
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- private protected int CommitDeselect(IReadOnlyList<IndexRange> ranges)
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+ /// <summary>
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+ /// If <see cref="RangesEnabled"/>, removes the specified range from the selection.
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+ /// </summary>
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+ /// <param name="begin">The inclusive index of the start of the range to deselect.</param>
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+ /// <param name="end">The inclusive index of the end of the range to deselect.</param>
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+ /// <returns>The number of items selected.</returns>
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+ protected int CommitDeselect(int begin, int end)
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{
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- if (RangesEnabled && _ranges is object)
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+ if (RangesEnabled)
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{
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- return IndexRange.Remove(_ranges, ranges);
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+ _ranges ??= new List<IndexRange>();
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+ return IndexRange.Remove(_ranges, new IndexRange(begin, end));
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}
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return 0;
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}
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- private protected virtual CollectionChangeState OnItemsAdded(int index, IList items)
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+ /// <summary>
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+ /// Called by <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>
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+ /// when items are added to the source collection.
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+ /// </summary>
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+ /// <returns>
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+ /// A <see cref="CollectionChangeState"/> struct containing the details of the adjusted
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+ /// selection.
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+ /// </returns>
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+ /// <remarks>
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+ /// The implementation in <see cref="SelectionNodeBase{T}"/> adjusts the selected ranges,
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+ /// assigning new indexes. Override this method to carry out additional computation when
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+ /// items are added.
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+ /// </remarks>
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+ protected virtual CollectionChangeState OnItemsAdded(int index, IList items)
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{
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var count = items.Count;
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var shifted = false;
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- if (_ranges is object)
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+ if (_ranges is not null)
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{
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List<IndexRange>? toAdd = null;
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@@ -150,7 +262,7 @@ namespace Avalonia.Controls.Selection
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// The range is after the inserted items, need to shift the range right
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if (range.End >= index)
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{
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- int begin = range.Begin;
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+ var begin = range.Begin;
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// If the index left of newIndex is inside the range,
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// Split the range and remember the left piece to add later
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@@ -167,7 +279,7 @@ namespace Avalonia.Controls.Selection
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}
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}
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- if (toAdd is object)
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+ if (toAdd is not null)
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{
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foreach (var range in toAdd)
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{
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@@ -183,14 +295,27 @@ namespace Avalonia.Controls.Selection
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};
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}
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+ /// <summary>
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+ /// Called by <see cref="OnSourceCollectionChanged(NotifyCollectionChangedEventArgs)"/>
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+ /// when items are removed from the source collection.
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+ /// </summary>
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+ /// <returns>
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+ /// A <see cref="CollectionChangeState"/> struct containing the details of the adjusted
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+ /// selection.
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+ /// </returns>
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+ /// <remarks>
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+ /// The implementation in <see cref="SelectionNodeBase{T}"/> adjusts the selected ranges,
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+ /// assigning new indexes. Override this method to carry out additional computation when
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+ /// items are removed.
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+ /// </remarks>
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private protected virtual CollectionChangeState OnItemsRemoved(int index, IList items)
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{
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var count = items.Count;
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var removedRange = new IndexRange(index, index + count - 1);
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- bool shifted = false;
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+ var shifted = false;
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List<T>? removed = null;
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- if (_ranges is object)
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+ if (_ranges is not null)
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{
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var deselected = new List<IndexRange>();
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@@ -227,60 +352,6 @@ namespace Avalonia.Controls.Selection
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};
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}
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- private protected virtual void OnSourceCollectionChanged(NotifyCollectionChangedEventArgs e)
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- {
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- var shiftDelta = 0;
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- var shiftIndex = -1;
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- List<T>? removed = null;
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-
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- if (!IsValidCollectionChange(e))
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- {
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- return;
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- }
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-
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- switch (e.Action)
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- {
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- case NotifyCollectionChangedAction.Add:
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- {
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- var change = OnItemsAdded(e.NewStartingIndex, e.NewItems!);
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- shiftIndex = change.ShiftIndex;
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- shiftDelta = change.ShiftDelta;
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- break;
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- }
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- case NotifyCollectionChangedAction.Remove:
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- {
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- var change = OnItemsRemoved(e.OldStartingIndex, e.OldItems!);
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- shiftIndex = change.ShiftIndex;
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- shiftDelta = change.ShiftDelta;
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- removed = change.RemovedItems;
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- break;
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- }
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- case NotifyCollectionChangedAction.Replace:
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- case NotifyCollectionChangedAction.Move:
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- {
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- var removeChange = OnItemsRemoved(e.OldStartingIndex, e.OldItems!);
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- var addChange = OnItemsAdded(e.NewStartingIndex, e.NewItems!);
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- shiftIndex = removeChange.ShiftIndex;
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- shiftDelta = removeChange.ShiftDelta + addChange.ShiftDelta;
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- removed = removeChange.RemovedItems;
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- }
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- break;
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- case NotifyCollectionChangedAction.Reset:
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- OnSourceReset();
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- break;
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- }
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-
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- if (shiftDelta != 0)
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- {
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- OnIndexesChanged(shiftIndex, shiftDelta);
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- }
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-
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- if (removed is object)
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- {
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- OnSelectionChanged(removed);
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- }
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- }
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-
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private protected virtual bool IsValidCollectionChange(NotifyCollectionChangedEventArgs e)
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{
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// If the selection is modified in a CollectionChanged handler before the selection
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@@ -309,11 +380,27 @@ namespace Avalonia.Controls.Selection
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return true;
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}
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- private protected struct CollectionChangeState
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+ /// <summary>
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+ /// Details the results of a collection change on the current selection;
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+ /// </summary>
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+ protected class CollectionChangeState
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{
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- public int ShiftIndex;
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- public int ShiftDelta;
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- public List<T>? RemovedItems;
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+ /// <summary>
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+ /// Gets or sets the first index that was shifted as a result of the collection
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+ /// changing.
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+ /// </summary>
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+ public int ShiftIndex { get; set; }
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+
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+ /// <summary>
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+ /// Gets or sets a value indicating how the indexes after <see cref="ShiftIndex"/>
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+ /// were shifted.
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+ /// </summary>
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+ public int ShiftDelta { get; set; }
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+
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+ /// <summary>
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+ /// Gets or sets the items removed by the collection change, if any.
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+ /// </summary>
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+ public List<T>? RemovedItems { get; set; }
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}
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}
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}
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Steven Kirk