Verify ContentsChanged Event is Only Unassigned if it Exists

Author: lukeblevins

Files UWP/Filesystem/ItemViewModel.cs

@@ -386,6 +386,14 @@ public async void AddItemsToCollectionAsync(string path, Page currentPage)
                 rootContentFrame.Navigate(typeof(InstanceTabsView), null, new SuppressNavigationTransitionInfo());
                 return;
             }
+            catch (FileNotFoundException)
+            {
+                Frame rootContentFrame = Window.Current.Content as Frame;
+                MessageDialog folderGone = new MessageDialog("The folder you've navigated to was removed.", "Did you delete this folder?");
+                await folderGone.ShowAsync();
+                rootContentFrame.Navigate(typeof(InstanceTabsView), null, new SuppressNavigationTransitionInfo());
+                return;
+            }
 
             if (typeof(PageType) == typeof(GenericFileBrowser))
             {

Files UWP/GenericFileBrowser.xaml.cs

@@ -161,7 +161,10 @@ protected override void OnNavigatedTo(NavigationEventArgs eventArgs)
         protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
         {
             base.OnNavigatingFrom(e);
-            instanceViewModel._fileQueryResult.ContentsChanged -= instanceViewModel.FileContentsChanged;
+            if(instanceViewModel._fileQueryResult != null)
+            {
+                instanceViewModel._fileQueryResult.ContentsChanged -= instanceViewModel.FileContentsChanged;
+            }
         }
 
 

Files UWP/PhotoAlbum.xaml.cs

@@ -119,7 +119,10 @@ protected override void OnNavigatedTo(NavigationEventArgs eventArgs)
         protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
         {
             base.OnNavigatingFrom(e);
-            instanceViewModel._fileQueryResult.ContentsChanged -= instanceViewModel.FileContentsChanged;
+            if (instanceViewModel._fileQueryResult != null)
+            {
+                instanceViewModel._fileQueryResult.ContentsChanged -= instanceViewModel.FileContentsChanged;
+            }
         }
 
         private void Clipboard_ContentChanged(object sender, object e)