Merge pull request #3811 from michael-hawker/fix-switchpresenter-logicaltree

Add ContentPresenter to Logical Tree helpers

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI/Extensions/FrameworkElement/FrameworkElementExtensions.LogicalTree.cs

@@ -153,43 +153,60 @@ public static partial class FrameworkElementExtensions
             }
             else if (element is ContentControl contentControl)
             {
-                if (contentControl.Content is T result && predicate.Match(result))
-                {
-                    return result;
-                }
-
                 if (contentControl.Content is FrameworkElement content)
                 {
+                    if (content is T result && predicate.Match(result))
+                    {
+                        return result;
+                    }
+
                     element = content;
 
                     goto Start;
                 }
             }
             else if (element is Border border)
             {
-                if (border.Child is T result && predicate.Match(result))
-                {
-                    return result;
-                }
-
                 if (border.Child is FrameworkElement child)
                 {
+                    if (child is T result && predicate.Match(result))
+                    {
+                        return result;
+                    }
+
                     element = child;
 
                     goto Start;
                 }
             }
+            else if (element is ContentPresenter contentPresenter)
+            {
+                // Sometimes ContentPresenter is used in control templates instead of ContentControl,
+                // therefore we should still check if its Content is a matching FrameworkElement instance.
+                // This also makes this work for SwitchPresenter.
+                if (contentPresenter.Content is FrameworkElement content)
+                {
+                    if (content is T result && predicate.Match(result))
+                    {
+                        return result;
+                    }
+
+                    element = content;
+
+                    goto Start;
+                }
+            }
             else if (element is UserControl userControl)
             {
                 // We put UserControl right before the slower reflection fallback path as
                 // this type is less likely to be used compared to the other ones above.
-                if (userControl.Content is T result && predicate.Match(result))
-                {
-                    return result;
-                }
-
                 if (userControl.Content is FrameworkElement content)
                 {
+                    if (content is T result && predicate.Match(result))
+                    {
+                        return result;
+                    }
+
                     element = content;
 
                     goto Start;
@@ -370,6 +387,17 @@ public static IEnumerable<FrameworkElement> FindChildren(this FrameworkElement e
                     goto Start;
                 }
             }
+            else if (element is ContentPresenter contentPresenter)
+            {
+                if (contentPresenter.Content is FrameworkElement content)
+                {
+                    yield return content;
+
+                    element = content;
+
+                    goto Start;
+                }
+            }
             else if (element is UserControl userControl)
             {
                 if (userControl.Content is FrameworkElement content)