Merge pull request #4872 from YohDeadfall/various-nullability-issues

Fixed invalid cast issue if source isn't visual and nullability warnings

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -354,19 +354,15 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         /// <param name="eventSource">The control that raised the event.</param>
         /// <returns>The container or null if the event did not originate in a container.</returns>
-        protected IControl? GetContainerFromEventSource(IInteractive eventSource)
+        protected IControl? GetContainerFromEventSource(IInteractive? eventSource)
         {
-            var parent = (IVisual)eventSource;
-
-            while (parent != null)
+            for (var current = eventSource as IVisual; current != null; current = current.VisualParent)
             {
-                if (parent is IControl control && control.LogicalParent == this
-                                               && ItemContainerGenerator?.IndexFromContainer(control) != -1)
+                if (current is IControl control && control.LogicalParent == this &&
+                    ItemContainerGenerator?.IndexFromContainer(control) != -1)
                 {
                     return control;
                 }
-
-                parent = parent.VisualParent;
             }
 
             return null;
@@ -670,7 +666,7 @@ namespace Avalonia.Controls.Primitives
         /// false.
         /// </returns>
         protected bool UpdateSelectionFromEventSource(
-            IInteractive eventSource,
+            IInteractive? eventSource,
             bool select = true,
             bool rangeModifier = false,
             bool toggleModifier = false,