Modify ScrollView to allow native measure in addition to content measure

src/Controls/src/Core/Layout.cs

@@ -219,12 +219,14 @@ protected virtual void OnChildMeasureInvalidated()
 
  Size IFrameworkElement.Measure(double widthConstraint, double heightConstraint)
  {
- DesiredSize = OnMeasure(widthConstraint, heightConstraint).Request;
- return DesiredSize;
+ return MeasureOverride(widthConstraint, heightConstraint);
  }
 
  protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
- => (this as IFrameworkElement).Measure(widthConstraint, heightConstraint);
+ {
+ DesiredSize = OnMeasure(widthConstraint, heightConstraint).Request;
+ return DesiredSize;
+ }
 
  protected override void OnSizeAllocated(double width, double height)
  {

src/Controls/src/Core/ScrollView.cs

@@ -276,9 +276,9 @@ protected override SizeRequest OnSizeRequest(double widthConstraint, double heig
 
  SizeRequest contentRequest;
 
- if (Content is IFrameworkElement fe && fe.Handler != null)
+ if (Content is IFrameworkElement fe)
  {
- contentRequest = fe.Handler.GetDesiredSize(widthConstraint, heightConstraint);
+ contentRequest = fe.Measure(widthConstraint, heightConstraint);
  }
  else
  {
@@ -362,5 +362,19 @@ void OnScrollToRequested(ScrollToRequestedEventArgs e)
  CheckTaskCompletionSource();
  ScrollToRequested?.Invoke(this, e);
  }
+
+ protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
+ {
+ // We call OnSizeRequest so that the content gets measured appropriately
+ // and then use the standard GetDesiredSize from the handler so the ScrollView's
+ // backing control gets measured. 
+
+ // TODO ezhart 2021-07-14 Verify that we've got the naming correct on this after we resolve the OnSizeRequest obsolete stuff
+#pragma warning disable CS0618 // Type or member is obsolete
+ _ = OnSizeRequest(widthConstraint, heightConstraint);
+#pragma warning restore CS0618 // Type or member is obsolete
+
+ return Handler.GetDesiredSize(widthConstraint, heightConstraint);
+ }
  }
 }

src/Core/src/Handlers/ScrollView/ScrollViewHandler.Windows.cs

@@ -21,14 +21,6 @@ protected override void ConnectHandler(ScrollViewer nativeView)
  nativeView.ViewChanged += ViewChanged;
  }
 
- public override void NativeArrange(Rectangle rect)
- {
- // Re-measure the content too, otherwise winui will try and keep the scrollviewer' size >= the content size
- NativeView?.Measure(new Windows.Foundation.Size(rect.Size.Width, rect.Size.Height));
-
- base.NativeArrange(rect);
- }
-
  protected override void DisconnectHandler(ScrollViewer nativeView)
  {
  base.DisconnectHandler(nativeView);