diff --git a/src/Avalonia.Controls/ItemsSourceView.cs b/src/Avalonia.Controls/ItemsSourceView.cs index 2884295386..d306939e4b 100644 --- a/src/Avalonia.Controls/ItemsSourceView.cs +++ b/src/Avalonia.Controls/ItemsSourceView.cs @@ -42,19 +42,16 @@ namespace Avalonia.Controls public ItemsSourceView(IEnumerable source) { source = source ?? throw new ArgumentNullException(nameof(source)); - - if (source is IList list) - { - _inner = list; - } - else if (source is IEnumerable objectEnumerable) + _inner = source switch { - _inner = new List(objectEnumerable); - } - else - { - _inner = new List(source.Cast()); - } + ItemsSourceView => throw new ArgumentException("Cannot wrap an existing ItemsSourceView.", nameof(source)), + IList list => list, + INotifyCollectionChanged => throw new ArgumentException( + "Collection implements INotifyCollectionChanged by not IList.", + nameof(source)), + IEnumerable iObj => new List(iObj), + _ => new List(source.Cast()) + }; } /// diff --git a/tests/Avalonia.Controls.UnitTests/ItemsSourceViewTests.cs b/tests/Avalonia.Controls.UnitTests/ItemsSourceViewTests.cs new file mode 100644 index 0000000000..529b3b1aa8 --- /dev/null +++ b/tests/Avalonia.Controls.UnitTests/ItemsSourceViewTests.cs @@ -0,0 +1,63 @@ +using System; +using System.Collections; +using System.Collections.Generic; +using System.Collections.Specialized; +using System.Text; +using Avalonia.Collections; +using Avalonia.Diagnostics; +using Xunit; + +namespace Avalonia.Controls.UnitTests +{ + public class ItemsSourceViewTests + { + [Fact] + public void Only_Subscribes_To_Source_CollectionChanged_When_CollectionChanged_Subscribed() + { + var source = new AvaloniaList(); + var target = new ItemsSourceView(source); + var debug = (INotifyCollectionChangedDebug)source; + + Assert.Null(debug.GetCollectionChangedSubscribers()); + + void Handler(object sender, NotifyCollectionChangedEventArgs e) { } + target.CollectionChanged += Handler; + + Assert.NotNull(debug.GetCollectionChangedSubscribers()); + Assert.Equal(1, debug.GetCollectionChangedSubscribers().Length); + + target.CollectionChanged -= Handler; + + Assert.Null(debug.GetCollectionChangedSubscribers()); + } + + [Fact] + public void Cannot_Wrap_An_ItemsSourceView_In_Another() + { + var source = new ItemsSourceView(new string[0]); + Assert.Throws(() => new ItemsSourceView(source)); + } + + [Fact] + public void Cannot_Create_ItemsSourceView_With_Collection_That_Implements_INCC_But_Not_List() + { + var source = new InvalidCollection(); + Assert.Throws(() => new ItemsSourceView(source)); + } + + private class InvalidCollection : INotifyCollectionChanged, IEnumerable + { + public event NotifyCollectionChangedEventHandler CollectionChanged; + + public IEnumerator GetEnumerator() + { + yield break; + } + + IEnumerator IEnumerable.GetEnumerator() + { + yield break; + } + } + } +}