Fix #122 - NullReferenceException in ItemAutomationPeer.GetNameCore() (…

…#7115)

For virtualized tree views it can happen that we are calling GetNameCore() on an item that has been scrolled out of view and doesn't have an associated container. ItemContainerGenerator.GetContainerFromItem() returns null, and so ItemsControlAutomationPeer ends up being null as well.

We're still going to retrieve the name from the item.ToString(), so it's much better than crashing here and aborting the entire layout pass.

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/ItemAutomationPeer.cs

@@ -527,9 +527,10 @@ protected override string GetNameCore()
             {
                 name = wrapperPeer.GetName();
             }
-            else if (item != null)
+            // see https://github.com/dotnet/wpf/issues/122
+            else if (item != null && ItemsControlAutomationPeer is { } itemsControlAutomationPeer)
             {
-                using (RecyclableWrapper recyclableWrapper = ItemsControlAutomationPeer.GetRecyclableWrapperPeer(item))
+                using (RecyclableWrapper recyclableWrapper = itemsControlAutomationPeer.GetRecyclableWrapperPeer(item))
                 {
                     name = recyclableWrapper.Peer.GetName();
                 }