Explicitly wait for UI Test App to load the Page for the Test before executing Test

Hopefully resolves issue with TAEF tests seen in the CI.

Author: michael-hawker

UITests/UITests.App/App.AppService.xaml.cs

@@ -53,9 +53,8 @@ private async void OnAppServiceRequestReceived(AppServiceConnection sender, AppS
 
                     if (host != null)
                     {
-                        // TODO: Think tried to make this async before but it blewup the runtime for some reason...
-                        // We'd like the OpenPage method to ensure the navigation has finished.
-                        if (host.OpenPage(pageName))
+                        // We await the OpenPage method to ensure the navigation has finished.
+                        if (await host.OpenPage(pageName))
                         {
                             returnMessage.Add("Status", "OK");
                         }

UITests/UITests.App/MainTestHost.xaml.cs

@@ -12,6 +12,7 @@
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Media.Animation;
 
 namespace UITests.App
 {
@@ -24,28 +25,37 @@ public sealed partial class MainTestHost
 
         private Assembly _executingAssembly = Assembly.GetExecutingAssembly();
 
+        private TaskCompletionSource<bool> _loadingStateTask;
+
         public MainTestHost()
         {
             InitializeComponent();
             ((App)Application.Current).host = this;
             _queue = DispatcherQueue.GetForCurrentThread();
         }
 
-        internal bool OpenPage(string pageName)
+        // TODO: we should better expose how to control the MainTestHost vs. making this internal.
+        internal async Task<bool> OpenPage(string pageName)
         {
             try
             {
                 Log.Comment("Trying to Load Page: " + pageName);
 
+                _loadingStateTask = new TaskCompletionSource<bool>();
+
                 // Ensure we're on the UI thread as we'll be called from the AppService now.
-                _queue.EnqueueAsync(() =>
+                _ = _queue.EnqueueAsync(() =>
                 {
-                    navigationFrame.Navigate(FindPageType(pageName));
+                    // Navigate without extra animations
+                    navigationFrame.Navigate(FindPageType(pageName), new SuppressNavigationTransitionInfo());
                 });
+
+                // Wait for load to complete
+                await _loadingStateTask.Task;
             }
             catch (Exception e)
             {
-                Log.Error("Exception Finding Page {0}: {1} ", pageName, e.Message);
+                Log.Error("Exception Loading Page {0}: {1} ", pageName, e.Message);
                 return false;
             }
 
@@ -69,11 +79,34 @@ private Type FindPageType(string pageName)
         private void NavigationFrame_Navigated(object sender, Windows.UI.Xaml.Navigation.NavigationEventArgs e)
         {
             Log.Comment("Navigated to Page {0}", e.SourcePageType.FullName);
+            if (e.Content is Page page)
+            {
+                if (page.IsLoaded)
+                {
+                    Log.Comment("Loaded Page {0}", e.SourcePageType.FullName);
+                    _loadingStateTask.SetResult(true);
+                }
+                else
+                {
+                    page.Loaded += this.Page_Loaded;
+                }
+            }
+        }
+
+        private void Page_Loaded(object sender, RoutedEventArgs e)
+        {
+            var page = sender as Page;
+
+            page.Loaded -= Page_Loaded;
+
+            Log.Comment("Loaded Page (E) {0}", page.GetType().FullName);
+            _loadingStateTask.SetResult(true);
         }
 
         private void NavigationFrame_NavigationFailed(object sender, Windows.UI.Xaml.Navigation.NavigationFailedEventArgs e)
         {
             Log.Error("Failed to navigate to page {0}", e.SourcePageType.FullName);
+            _loadingStateTask.SetResult(false);
         }
     }
 }