refactor: remove possible null reference

Screenbox/Pages/AlbumDetailsPage.xaml.cs

@@ -76,7 +76,7 @@ private void AlbumDetailsPage_OnLoaded(object sender, RoutedEventArgs e)
             // Get references to our property sets for use with ExpressionNodes
             ManipulationPropertySetReferenceNode scrollingProperties = _scrollerPropertySet.GetSpecializedReference<ManipulationPropertySetReferenceNode>();
 
-            CreateHeaderAnimation(scrollingProperties.Translation.Y);
+            CreateHeaderAnimation(_props, scrollingProperties.Translation.Y);
             MediaViewModel firstSong = ViewModel.Source.RelatedSongs[0];
             if (firstSong.ThumbnailSource != null)
             {
@@ -90,6 +90,7 @@ private void AlbumDetailsPage_OnLoaded(object sender, RoutedEventArgs e)
 
         private void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
         {
+            if (_scrollerPropertySet == null) return;
             MediaViewModel media = (MediaViewModel)sender;
             if (e.PropertyName == nameof(MediaViewModel.Thumbnail) && media.ThumbnailSource != null)
             {
@@ -99,16 +100,16 @@ private void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
             }
         }
 
-        private void CreateHeaderAnimation(ScalarNode scrollVerticalOffset)
+        private void CreateHeaderAnimation(CompositionPropertySet propSet, ScalarNode scrollVerticalOffset)
         {
-            PropertySetReferenceNode props = _props.GetReference();
+            PropertySetReferenceNode props = propSet.GetReference();
             ScalarNode progressNode = props.GetScalarProperty("progress");
             ScalarNode clampSizeNode = props.GetScalarProperty("clampSize");
             ScalarNode bottomMarginNode = props.GetScalarProperty("bottomMargin");
 
             // Create and start an ExpressionAnimation to track scroll progress over the desired distance
             ExpressionNode progressAnimation = EF.Clamp(-scrollVerticalOffset / clampSizeNode, 0, 1);
-            _props.StartAnimation("progress", progressAnimation);
+            propSet.StartAnimation("progress", progressAnimation);
 
             // Get the backing visual for the photo in the header so that its properties can be animated
             Visual photoVisual = ElementCompositionPreview.GetElementVisual(BackgroundAcrylic);

Screenbox/Pages/ArtistDetailsPage.xaml.cs

@@ -65,19 +65,19 @@ private void ArtistDetailsPage_OnLoaded(object sender, RoutedEventArgs e)
             // Get references to our property sets for use with ExpressionNodes
             ManipulationPropertySetReferenceNode scrollingProperties = _scrollerPropertySet.GetSpecializedReference<ManipulationPropertySetReferenceNode>();
 
-            CreateHeaderAnimation(scrollingProperties.Translation.Y);
+            CreateHeaderAnimation(_props, scrollingProperties.Translation.Y);
         }
 
-        private void CreateHeaderAnimation(ScalarNode scrollVerticalOffset)
+        private void CreateHeaderAnimation(CompositionPropertySet propSet, ScalarNode scrollVerticalOffset)
         {
-            PropertySetReferenceNode props = _props.GetReference();
+            PropertySetReferenceNode props = propSet.GetReference();
             ScalarNode progressNode = props.GetScalarProperty("progress");
             ScalarNode clampSizeNode = props.GetScalarProperty("clampSize");
             ScalarNode bottomMarginNode = props.GetScalarProperty("bottomMargin");
 
             // Create and start an ExpressionAnimation to track scroll progress over the desired distance
             ExpressionNode progressAnimation = EF.Clamp(-scrollVerticalOffset / clampSizeNode, 0, 1);
-            _props.StartAnimation("progress", progressAnimation);
+            propSet.StartAnimation("progress", progressAnimation);
 
             // Get the backing visual for the photo in the header so that its properties can be animated
             Visual photoVisual = ElementCompositionPreview.GetElementVisual(BackgroundAcrylic);