ListDetailsView unfocus content on SelectedIndex changed.

Microsoft.Toolkit.Uwp.UI.Controls.Layout/ListDetailsView/ListDetailsView.cs

@@ -163,6 +163,7 @@ private void OnSelectedItemChanged(DependencyPropertyChangedEventArgs e)
 
             OnSelectionChanged(new SelectionChangedEventArgs(new List<object> { e.OldValue }, new List<object> { e.NewValue }));
             UpdateView(true);
+            SetFocus(ViewState);
         }
 
         private void OnLoaded(object sender, RoutedEventArgs e)
@@ -405,7 +406,7 @@ private void FocusFirstFocusableElementInDetails()
         /// </summary>
         private void FocusItemList()
         {
-            if (GetTemplateChild("PartMainList") is Control list)
+            if (GetTemplateChild(PartMainList) is Control list)
             {
                 list.Focus(FocusState.Programmatic);
             }

UnitTests/UnitTests.UWP/UI/Controls/Test_ListDetailsView_UI.cs

@@ -0,0 +1,112 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.Toolkit.Uwp;
+using Microsoft.Toolkit.Uwp.UI;
+using Microsoft.Toolkit.Uwp.UI.Controls;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.ObjectModel;
+using System.Threading.Tasks;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Markup;
+
+namespace UnitTests.UWP.UI.Controls
+{
+    [TestClass]
+    public class Test_ListDetailsView_UI : VisualUITestBase
+    {
+        private const string SampleXaml = @"<controls:ListDetailsView
+                                                    xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
+                                                    xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
+                                                    xmlns:controls=""using:Microsoft.Toolkit.Uwp.UI.Controls""
+                                                    NoSelectionContent=""No item selected"" >
+                                                    <controls:ListDetailsView.ItemTemplate>
+                                                        <DataTemplate>
+                                                            <TextBlock Text=""Item"" />
+                                                        </DataTemplate>
+                                                    </controls:ListDetailsView.ItemTemplate>
+                                                    <controls:ListDetailsView.DetailsTemplate>
+                                                        <DataTemplate>
+                                                            <TextBox Text=""{Binding}"" />
+                                                        </DataTemplate>
+                                                    </controls:ListDetailsView.DetailsTemplate>
+                                                 </controls:ListDetailsView>";
+
+        [TestCategory("ListDetailsView")]
+        [TestMethod]
+        public async Task Test_LoseFocusOnNoSelection()
+        {
+            await App.DispatcherQueue.EnqueueAsync(async () =>
+            {
+                var listDetailsView = XamlReader.Load(SampleXaml) as ListDetailsView;
+
+                listDetailsView.ItemsSource = new ObservableCollection<string>
+                {
+                     "First",
+                };
+
+                listDetailsView.SelectedIndex = 0;
+
+                await SetTestContentAsync(listDetailsView);
+
+                var firsttb = listDetailsView.FindDescendant<TextBox>();
+
+                await App.DispatcherQueue.EnqueueAsync(() => firsttb.Focus(FocusState.Programmatic));
+
+                Assert.AreEqual(firsttb, FocusManager.GetFocusedElement(), "TextBox didn't get focus");
+
+                var tcs = new TaskCompletionSource<bool>();
+
+                firsttb.LostFocus += (s, e) => tcs.SetResult(true);
+
+                listDetailsView.SelectedIndex = -1;
+
+                await Task.WhenAny(tcs.Task, Task.Delay(2000));
+
+                Assert.IsTrue(tcs.Task.IsCompleted);
+                Assert.IsTrue(tcs.Task.Result, "TextBox in the first item should have lost focus.");
+            });
+        }
+
+        [TestCategory("ListDetailsView")]
+        [TestMethod]
+        public async Task Test_LoseFocusOnSelectOther()
+        {
+            await App.DispatcherQueue.EnqueueAsync(async () =>
+            {
+                var listDetailsView = XamlReader.Load(SampleXaml) as ListDetailsView;
+
+                listDetailsView.ItemsSource = new ObservableCollection<string>
+                {
+                     "First",
+                     "Second",
+                };
+
+                listDetailsView.SelectedIndex = 0;
+
+                await SetTestContentAsync(listDetailsView);
+
+                var firsttb = listDetailsView.FindDescendant<TextBox>();
+
+                await App.DispatcherQueue.EnqueueAsync(() => firsttb.Focus(FocusState.Programmatic));
+
+                Assert.AreEqual(firsttb, FocusManager.GetFocusedElement(), "TextBox didn't get focus");
+
+                var tcs = new TaskCompletionSource<bool>();
+
+                firsttb.LostFocus += (s, e) => tcs.SetResult(true);
+
+                listDetailsView.SelectedIndex = 1;
+
+                await Task.WhenAny(tcs.Task, Task.Delay(2000));
+
+                Assert.IsTrue(tcs.Task.IsCompleted);
+                Assert.IsTrue(tcs.Task.Result, "TextBox in the first item should have lost focus.");
+            });
+        }
+    }
+}

UnitTests/UnitTests.UWP/UnitTests.UWP.csproj

@@ -237,6 +237,7 @@
     <Compile Include="UI\Controls\Test_ConstrainedBox.Multiple.cs" />
     <Compile Include="UI\Controls\Test_ConstrainedBox.Combined.cs" />
     <Compile Include="UI\Controls\Test_ImageEx.cs" />
+    <Compile Include="UI\Controls\Test_ListDetailsView_UI.cs" />
     <Compile Include="UI\Controls\Test_RadialGauge.cs" />
     <Compile Include="UI\Controls\Test_RichSuggestBox.cs" />
     <Compile Include="UI\Controls\Test_TextToolbar_Localization.cs" />