Avoid recreating IMarkdownPreview control (#6153)

* Avoid recreating markdown control

* Remove MarkdownPreview depdency property

* Pass IMarkdownPreview into the viewmodel instead of building it there

* Add missing using statement

* fix merge

* Move to singleton

* Remove creating instance in tab control

* pr comment

src/NuGet.Clients/NuGet.PackageManagement.UI/Utility/MarkdownPreviewSingleton.cs

@@ -0,0 +1,37 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.VisualStudio.Markdown.Platform;
+
+namespace NuGet.PackageManagement.UI
+{
+    public class MarkdownPreviewSingleton
+    {
+#pragma warning disable CS0618 // Type or member is obsolete
+        private static IMarkdownPreview Instance;
+#pragma warning restore CS0618 // Type or member is obsolete
+
+#pragma warning disable CS0618 // Type or member is obsolete
+        public static IMarkdownPreview GetInstance()
+#pragma warning restore CS0618 // Type or member is obsolete
+        {
+            if (Instance == null)
+            {
+#pragma warning disable CS0618 // Type or member is obsolete
+                Instance = new PreviewBuilder().Build();
+#pragma warning restore CS0618 // Type or member is obsolete
+            }
+
+            return Instance;
+        }
+
+        public static void ResetInstance()
+        {
+            if (Instance != null)
+            {
+                Instance.Dispose();
+                Instance = null;
+            }
+        }
+    }
+}

src/NuGet.Clients/NuGet.PackageManagement.UI/ViewModels/PackageDetailsTabViewModel.cs

@@ -38,8 +38,9 @@ public async Task InitializeAsync(DetailControlModel detailControlModel, INuGetP
         {
             var nuGetFeatureFlagService = await ServiceLocator.GetComponentModelServiceAsync<INuGetFeatureFlagService>();
             _readmeTabEnabled = await nuGetFeatureFlagService.IsFeatureEnabledAsync(NuGetFeatureFlagConstants.RenderReadmeInPMUI);
-
+#pragma warning disable CS0618 // Type or member is obsolete
             ReadmePreviewViewModel = new ReadmePreviewViewModel(nugetPackageFileService, currentFilter, _readmeTabEnabled);
+#pragma warning restore CS0618 // Type or member is obsolete
             DetailControlModel = detailControlModel;
 
             if (_readmeTabEnabled)
@@ -76,7 +77,6 @@ public void Dispose()
             }
             _disposed = true;
             DetailControlModel.PropertyChanged -= DetailControlModel_PropertyChanged;
-
             foreach (var tab in Tabs)
             {
                 tab.PropertyChanged -= IsVisible_PropertyChanged;

src/NuGet.Clients/NuGet.PackageManagement.UI/ViewModels/ReadmePreviewViewModel.cs

@@ -20,7 +20,9 @@ public sealed class ReadmePreviewViewModel : TitledPageViewModelBase
         private bool _canRenderLocalReadme;
         private bool _isBusy;
 
+#pragma warning disable CS0618 // Type or member is obsolete
         public ReadmePreviewViewModel(INuGetPackageFileService packageFileService, ItemFilter itemFilter, bool isReadmeFeatureEnabled)
+#pragma warning restore CS0618 // Type or member is obsolete
         {
             _nugetPackageFileService = packageFileService ?? throw new ArgumentNullException(nameof(packageFileService));
             _canRenderLocalReadme = CanRenderLocalReadme(itemFilter);

src/NuGet.Clients/NuGet.PackageManagement.UI/Xamls/DetailControl.xaml.cs

@@ -104,6 +104,11 @@ public void Refresh()
             }).PostOnFailure(nameof(DetailControl));
         }
 
+        public void Cleanup()
+        {
+            _packageDetailsTabControl.Dispose();
+        }
+
         private void ProjectInstallButtonClicked(object sender, EventArgs e)
         {
             var model = (PackageDetailControlModel)DataContext;

src/NuGet.Clients/NuGet.PackageManagement.UI/Xamls/PackageDetailsTabControl.xaml.cs

@@ -41,6 +41,7 @@ protected virtual void Dispose(bool disposing)
             if (disposing)
             {
                 PackageDetailsTabViewModel.Dispose();
+                MarkdownPreviewSingleton.ResetInstance();
             }
             _disposed = true;
         }

src/NuGet.Clients/NuGet.PackageManagement.UI/Xamls/PackageManagerControl.xaml.cs

@@ -1580,6 +1580,7 @@ private void CleanUp()
             _refreshCts?.Dispose();
             _cancelSelectionChangedSource?.Dispose();
 
+            _packageDetail.Cleanup();
             _detailModel.Dispose();
             _packageList.SelectionChanged -= PackageList_SelectionChanged;
 

src/NuGet.Clients/NuGet.PackageManagement.UI/Xamls/PackageReadmeControl.xaml

@@ -28,14 +28,13 @@
   <Grid>
     <ContentControl
       x:Name="descriptionMarkdownPreview"
-      x:Uid="descriptionMarkdownPreview"
       ClipToBounds="True"
       Focusable="False"
-      Visibility="{Binding Path=IsReadmeReady, Mode=OneWay, Converter={StaticResource BooleanToVisibilityConverter}}" />
+      Visibility="{Binding Path=IsReadmeReady, Mode=OneWay, FallbackValue=Collapsed, Converter={StaticResource BooleanToVisibilityConverter}}" />
     <Grid
       HorizontalAlignment="Center"
       VerticalAlignment="Center"
-      Visibility="{Binding Path=IsBusy, Mode=OneWay, Converter={StaticResource BooleanToVisibilityConverter}}" >
+      Visibility="{Binding Path=IsBusy, Mode=OneWay, FallbackValue=Visible, Converter={StaticResource BooleanToVisibilityConverter}}" >
       <Grid.ColumnDefinitions>
         <ColumnDefinition Width="Auto"/>
         <ColumnDefinition Width="Auto"/>
@@ -75,6 +74,6 @@
     <TextBlock
       TextWrapping="Wrap"
       Text="{x:Static nuget:Resources.Error_UnableToLoadReadme}"
-      Visibility="{Binding Path=ErrorWithReadme, Mode=OneWay, Converter={StaticResource BooleanToVisibilityConverter}}" />
+      Visibility="{Binding Path=ErrorWithReadme, Mode=OneWay, FallbackValue=Collapsed, Converter={StaticResource BooleanToVisibilityConverter}}" />
   </Grid>
 </UserControl>

src/NuGet.Clients/NuGet.PackageManagement.UI/Xamls/PackageReadmeControl.xaml.cs

@@ -7,6 +7,7 @@
 using System.Windows;
 using System.Windows.Controls;
 using Microsoft.VisualStudio.Markdown.Platform;
+using Microsoft.VisualStudio.Shell;
 using NuGet.PackageManagement.UI.ViewModels;
 using NuGet.VisualStudio;
 using NuGet.VisualStudio.Telemetry;
@@ -16,19 +17,17 @@ namespace NuGet.PackageManagement.UI
     /// <summary>
     /// Interaction logic for PackageReadmeControl.xaml
     /// </summary>
-    public partial class PackageReadmeControl : UserControl, IDisposable
+    public partial class PackageReadmeControl : UserControl
     {
 #pragma warning disable CS0618 // Type or member is obsolete
         private IMarkdownPreview _markdownPreview;
 #pragma warning restore CS0618 // Type or member is obsolete
-        private bool _disposed = false;
 
         public PackageReadmeControl()
         {
             InitializeComponent();
-#pragma warning disable CS0618 // Type or member is obsolete
-            _markdownPreview = new PreviewBuilder().Build();
-#pragma warning restore CS0618 // Type or member is obsolete
+            _markdownPreview = MarkdownPreviewSingleton.GetInstance();
+            descriptionMarkdownPreview.Content = _markdownPreview.VisualElement;
         }
 
         public ReadmePreviewViewModel ReadmeViewModel { get => (ReadmePreviewViewModel)DataContext; }
@@ -41,36 +40,10 @@ private void ReadmeViewModel_PropertyChanged(object sender, PropertyChangedEvent
             }
         }
 
-        public void Dispose()
-        {
-            Dispose(disposing: true);
-            GC.SuppressFinalize(this);
-        }
-
-        protected virtual void Dispose(bool disposing)
-        {
-            if (_disposed)
-            {
-                return;
-            }
-
-            if (disposing)
-            {
-                _markdownPreview?.Dispose();
-                if (ReadmeViewModel is not null)
-                {
-                    ReadmeViewModel.PropertyChanged -= ReadmeViewModel_PropertyChanged;
-                }
-            }
-
-            _disposed = true;
-        }
-
         private async Task UpdateMarkdownAsync()
         {
             try
             {
-                descriptionMarkdownPreview.Content = descriptionMarkdownPreview.Content ?? _markdownPreview.VisualElement;
                 if (!string.IsNullOrWhiteSpace(ReadmeViewModel.ReadmeMarkdown))
                 {
                     await _markdownPreview.UpdateContentAsync(ReadmeViewModel.ReadmeMarkdown, ScrollHint.None);
@@ -88,6 +61,10 @@ private void UserControl_DataContextChanged(object sender, DependencyPropertyCha
         {
             if (e.OldValue is ReadmePreviewViewModel oldMetadata)
             {
+                ThreadHelper.JoinableTaskFactory.Run(async () =>
+                {
+                    await _markdownPreview.UpdateContentAsync("", ScrollHint.None);
+                });
                 oldMetadata.PropertyChanged -= ReadmeViewModel_PropertyChanged;
             }
             if (ReadmeViewModel is not null)
@@ -98,13 +75,19 @@ private void UserControl_DataContextChanged(object sender, DependencyPropertyCha
 
         private void PackageReadmeControl_Unloaded(object sender, RoutedEventArgs e)
         {
-            Dispose();
+            if (ReadmeViewModel is not null)
+            {
+                ThreadHelper.JoinableTaskFactory.Run(async () =>
+                {
+                    await _markdownPreview.UpdateContentAsync("", ScrollHint.None);
+                });
+                ReadmeViewModel.PropertyChanged -= ReadmeViewModel_PropertyChanged;
+            }
         }
 
         private void PackageReadmeControl_Loaded(object sender, RoutedEventArgs e)
         {
-            NuGetUIThreadHelper.JoinableTaskFactory.RunAsync(UpdateMarkdownAsync)
-                .PostOnFailure(nameof(PackageReadmeControl), nameof(PackageReadmeControl_Loaded));
+            NuGetUIThreadHelper.JoinableTaskFactory.Run(UpdateMarkdownAsync);
         }
     }
 }