Lazy load VSGitExt on Main thread

Make PullRequestStatusBarPackage load on background thread.
The VSGitExt MEF service must be loaded on the Main thread.

Author: jcansdale

src/GitHub.InlineReviews/PullRequestStatusBarPackage.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Windows;
 using System.Threading;
 using System.Runtime.InteropServices;
 using Microsoft.VisualStudio.Shell;
@@ -10,9 +9,9 @@
 
 namespace GitHub.InlineReviews
 {
-    [PackageRegistration(UseManagedResourcesOnly = true)]
     [Guid(Guids.PullRequestStatusPackageId)]
-    [ProvideAutoLoad(Guids.GitSccProviderId)]
+    [PackageRegistration(UseManagedResourcesOnly = true, AllowsBackgroundLoading = true)]
+    [ProvideAutoLoad(Guids.GitSccProviderId, PackageAutoLoadFlags.BackgroundLoad)]
     public class PullRequestStatusBarPackage : AsyncPackage
     {
         /// <summary>
@@ -23,7 +22,7 @@ protected override async Task InitializeAsync(CancellationToken cancellationToke
             var componentModel = (IComponentModel)await GetServiceAsync(typeof(SComponentModel));
             var exportProvider = componentModel.DefaultExportProvider;
             var pullRequestStatusManager = exportProvider.GetExportedValue<IPullRequestStatusBarManager>();
-            pullRequestStatusManager.Initialize(Application.Current.MainWindow);
+            await pullRequestStatusManager.InitializeAsync();
         }
     }
 }

src/GitHub.InlineReviews/Services/IPullRequestStatusBarManager.cs

@@ -1,4 +1,4 @@
-using System.Windows;
+using System.Threading.Tasks;
 
 namespace GitHub.InlineReviews.Services
 {
@@ -7,7 +7,6 @@ public interface IPullRequestStatusBarManager
         /// <summary>
         /// Place the PR status control on Visual Studio's status bar.
         /// </summary>
-        /// <param name="mainWindow">The main window of Visual Studio.</param>
-        void Initialize(Window mainWindow);
+        Task InitializeAsync();
     }
 }

src/GitHub.InlineReviews/Services/PullRequestStatusBarManager.cs

@@ -24,15 +24,13 @@ public class PullRequestStatusBarManager : IPullRequestStatusBarManager
         static readonly ILogger log = LogManager.ForContext<PullRequestStatusBarManager>();
         const string StatusBarPartName = "PART_SccStatusBarHost";
 
-        readonly IVSGitExt gitExt;
+        readonly Lazy<IVSGitExt> gitExt;
         readonly Lazy<IPullRequestSessionManager> pullRequestSessionManager;
         readonly IUsageTracker usageTracker;
         readonly IGitHubServiceProvider serviceProvider;
 
-        Window mainWindow;
-
         [ImportingConstructor]
-        public PullRequestStatusBarManager(IVSGitExt gitExt, Lazy<IPullRequestSessionManager> pullRequestSessionManager,
+        public PullRequestStatusBarManager(Lazy<IVSGitExt> gitExt, Lazy<IPullRequestSessionManager> pullRequestSessionManager,
             IUsageTracker usageTracker, IGitHubServiceProvider serviceProvider)
         {
             this.gitExt = gitExt;
@@ -45,23 +43,24 @@ public PullRequestStatusBarManager(IVSGitExt gitExt, Lazy<IPullRequestSessionMan
         /// Lazily initialize when user enters the context of a GitHub repository.
         /// </summary>
         /// <param name="window">Visual Studio's main window.</param>
-        public void Initialize(Window window)
+        public async Task InitializeAsync()
         {
-            mainWindow = window;
+            await ThreadingHelper.SwitchToMainThreadAsync();
+
             OnActiveRepositoriesChanged();
-            gitExt.ActiveRepositoriesChanged += OnActiveRepositoriesChanged;
+            gitExt.Value.ActiveRepositoriesChanged += OnActiveRepositoriesChanged;
         }
 
         void OnActiveRepositoriesChanged()
         {
-            if (gitExt.ActiveRepositories.Count > 0)
+            if (gitExt.Value.ActiveRepositories.Count > 0)
             {
-                InitializeAsync().Forget();
-                gitExt.ActiveRepositoriesChanged -= OnActiveRepositoriesChanged;
+                StartShowingStatus().Forget();
+                gitExt.Value.ActiveRepositoriesChanged -= OnActiveRepositoriesChanged;
             }
         }
 
-        async Task InitializeAsync()
+        async Task StartShowingStatus()
         {
             try
             {
@@ -103,7 +102,7 @@ PullRequestStatusViewModel CreatePullRequestStatusViewModel(IPullRequestModel pu
 
         void ShowStatus(PullRequestStatusViewModel pullRequestStatusViewModel = null)
         {
-            var statusBar = FindSccStatusBar();
+            var statusBar = FindSccStatusBar(Application.Current.MainWindow);
             if (statusBar != null)
             {
                 var githubStatusBar = Find<PullRequestStatusView>(statusBar);
@@ -134,7 +133,7 @@ static T Find<T>(StatusBar statusBar)
             return default(T);
         }
 
-        StatusBar FindSccStatusBar()
+        StatusBar FindSccStatusBar(Window mainWindow)
         {
             var contentControl = mainWindow?.Template?.FindName(StatusBarPartName, mainWindow) as ContentControl;
             return contentControl?.Content as StatusBar;