[LottieViewer] PixelView bug fixed. We should not update pixel view when it is not on the screen. (#475)

Author: aborziak-ms

LottieViewer/MainPage.xaml.cs

@@ -421,6 +421,11 @@ void ControlPanelButtonChecked(object sender, RoutedEventArgs e)
                 ControlPanel.Children.Add(ColorPanel);
             }
 
+            // PixelView should be active only when Info page is open.
+            // Otherwise changing surface that is not yet on the screen
+            // will throw an exception.
+            _pixelView.Active = sender == InfoButton;
+
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsControlPanelVisible)));
         }
 
@@ -433,6 +438,11 @@ void ControlPanelButtonUnchecked(object sender, RoutedEventArgs e)
             // trigger the PaneThemeTransition so that the pane slides in and out.
             ControlPanel.Children.Clear();
 
+            // PixelView should be active only when Info page is open.
+            // Otherwise changing surface that is not yet on the screen
+            // will throw an exception.
+            _pixelView.Active = false;
+
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsControlPanelVisible)));
         }
 

LottieViewer/PixelViewElement.cs

@@ -33,6 +33,9 @@ public sealed class PixelViewElement : UserControl
         readonly SpriteVisual _spriteVisual;
         Visual? _capturedVisual = null;
 
+        // Indicates if PixelView should update the image.
+        public bool Active { get; set; } = false;
+
         // Checkerboard pattern bitmap.
         static CanvasBitmap? _patternBitmap = null;
 
@@ -171,10 +174,13 @@ async Task ShowBitmapOnTargetAsync(CanvasBitmap bitmap)
 
         void OnFrameArrived(Direct3D11CaptureFramePool sender, object args)
         {
-            using (var frame = sender.TryGetNextFrame())
+            if (Active)
             {
-                CanvasBitmap bitmap = CanvasBitmap.CreateFromDirect3D11Surface(_canvasDevice!, frame.Surface);
-                _ = ShowBitmapOnTargetAsync(bitmap);
+                using (var frame = sender.TryGetNextFrame())
+                {
+                    CanvasBitmap bitmap = CanvasBitmap.CreateFromDirect3D11Surface(_canvasDevice!, frame.Surface);
+                    _ = ShowBitmapOnTargetAsync(bitmap);
+                }
             }
         }