Make sure transition from empty CollectionView measures cell size; fixes

xamarin#7472 (xamarin#7580) fixes xamarin#7472 fixes xamarin#7548
felipebaltazar · Oct 16, 2019 · ed57fe3 · ed57fe3
1 parent 3aeee7a
commit ed57fe3
Show file tree

Hide file tree

Showing 3 changed files with 43 additions and 28 deletions.
diff --git a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs
@@ -14,26 +14,29 @@ public class CollectionViewGallery : ContentPage
 	{
 		public CollectionViewGallery()
 		{
-			Content = new StackLayout
+			Content = new ScrollView
 			{
-				Children =
-				{   
-					new Button { Text ="Enable CollectionView", AutomationId = "EnableCollectionView", Command = new Command(() => Device.SetFlags(new[] { ExperimentalFlags.CollectionViewExperimental })) },
-					GalleryBuilder.NavButton("Default Text Galleries", () => new DefaultTextGallery(), Navigation),
-					GalleryBuilder.NavButton("DataTemplate Galleries", () => new DataTemplateGallery(), Navigation),
-					GalleryBuilder.NavButton("Observable Collection Galleries", () => new ObservableCollectionGallery(), Navigation),
-					GalleryBuilder.NavButton("Snap Points Galleries", () => new SnapPointsGallery(), Navigation),
-					GalleryBuilder.NavButton("ScrollTo Galleries", () => new ScrollToGallery(), Navigation),
-					GalleryBuilder.NavButton("CarouselView Galleries", () => new CarouselViewGallery(), Navigation),
-					GalleryBuilder.NavButton("EmptyView Galleries", () => new EmptyViewGallery(), Navigation),
-					GalleryBuilder.NavButton("Selection Galleries", () => new SelectionGallery(), Navigation),
-					GalleryBuilder.NavButton("Propagation Galleries", () => new PropagationGallery(), Navigation),
-					GalleryBuilder.NavButton("Grouping Galleries", () => new GroupingGallery(), Navigation),
-					GalleryBuilder.NavButton("Item Size Galleries", () => new ItemsSizeGallery(), Navigation),
-					GalleryBuilder.NavButton("Scroll Mode Galleries", () => new ScrollModeGallery(), Navigation),
-					GalleryBuilder.NavButton("Alternate Layout Galleries", () => new AlternateLayoutGallery(), Navigation),
-					GalleryBuilder.NavButton("Header/Footer Galleries", () => new HeaderFooterGallery(), Navigation),
-					GalleryBuilder.NavButton("Nested CollectionViews", () => new NestedGalleries.NestedCollectionViewGallery(), Navigation),
+				Content = new StackLayout
+				{
+					Children =
+					{
+						new Button { Text ="Enable CollectionView", AutomationId = "EnableCollectionView", Command = new Command(() => Device.SetFlags(new[] { ExperimentalFlags.CollectionViewExperimental })) },
+						GalleryBuilder.NavButton("Default Text Galleries", () => new DefaultTextGallery(), Navigation),
+						GalleryBuilder.NavButton("DataTemplate Galleries", () => new DataTemplateGallery(), Navigation),
+						GalleryBuilder.NavButton("Observable Collection Galleries", () => new ObservableCollectionGallery(), Navigation),
+						GalleryBuilder.NavButton("Snap Points Galleries", () => new SnapPointsGallery(), Navigation),
+						GalleryBuilder.NavButton("ScrollTo Galleries", () => new ScrollToGallery(), Navigation),
+						GalleryBuilder.NavButton("CarouselView Galleries", () => new CarouselViewGallery(), Navigation),
+						GalleryBuilder.NavButton("EmptyView Galleries", () => new EmptyViewGallery(), Navigation),
+						GalleryBuilder.NavButton("Selection Galleries", () => new SelectionGallery(), Navigation),
+						GalleryBuilder.NavButton("Propagation Galleries", () => new PropagationGallery(), Navigation),
+						GalleryBuilder.NavButton("Grouping Galleries", () => new GroupingGallery(), Navigation),
+						GalleryBuilder.NavButton("Item Size Galleries", () => new ItemsSizeGallery(), Navigation),
+						GalleryBuilder.NavButton("Scroll Mode Galleries", () => new ScrollModeGallery(), Navigation),
+						GalleryBuilder.NavButton("Alternate Layout Galleries", () => new AlternateLayoutGallery(), Navigation),
+						GalleryBuilder.NavButton("Header/Footer Galleries", () => new HeaderFooterGallery(), Navigation),
+						GalleryBuilder.NavButton("Nested CollectionViews", () => new NestedGalleries.NestedCollectionViewGallery(), Navigation),
+					}
 				}
 			};
 		}

diff --git a/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs b/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
@@ -112,6 +112,14 @@ void CheckForEmptySource()
 			{
 				UpdateEmptyViewVisibility(_isEmpty);
 			}
+
+			if (wasEmpty && !_isEmpty)
+			{
+				// If we're going from empty to having stuff, it's possible that we've never actually measured
+				// a prototype cell and our itemSize or estimatedItemSize are wrong/unset
+				// So trigger a constraint update; if we need a measurement, that will make it happen
+				ItemsViewLayout.ConstrainTo(CollectionView.Bounds.Size);
+			}
 		}
 
 		public override void ViewDidLoad()

diff --git a/Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs b/Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs
@@ -135,17 +135,21 @@ void Add(NotifyCollectionChangedEventArgs args)
 			var startIndex = args.NewStartingIndex > -1 ? args.NewStartingIndex : _itemsSource.IndexOf(args.NewItems[0]);
 			var count = args.NewItems.Count;
 
-			_collectionView.PerformBatchUpdates(() =>
+			if (!_grouped && _collectionView.NumberOfSections() != GroupCount && count > 0)
 			{
-				if (!_grouped && _collectionView.NumberOfSections() != GroupCount)
+				// Okay, we're going from completely empty to more than 0 items; this means we don't even
+				// have a section 0 yet. Inserting a section 0 manually results in an unexplained crash, so instead
+				// we'll just reload the data so the UICollectionView can get its internal state sorted out.
+				_collectionView.ReloadData();
+			}
+			else
+			{
+				_collectionView.PerformBatchUpdates(() =>
 				{
-					// We had an empty non-grouped list, and now we're trying to add an item;
-					// we need to give it a section as well
-					_collectionView.InsertSections(new NSIndexSet(0));
-				}
-
-				_collectionView.InsertItems(CreateIndexesFrom(startIndex, count));
-			}, null);
+					var indexes = CreateIndexesFrom(startIndex, count);
+					_collectionView.InsertItems(indexes);
+				}, null);
+			}
 		}
 
 		void Remove(NotifyCollectionChangedEventArgs args)