Make sure transition from empty CollectionView measures cell size; fixes #7472 (...

fixes #7472
fixes #7548

diff --git a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs
index 6e2e5d8a40e730683966324070824f9bd7bf5524..be9b989579fe2365737a589eaf42fb21a9193841 100644 (file)
--- a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs
+++ b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionViewGallery.cs
@@ -14,26 +14,29 @@ namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries
        {
                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
index a8ffeb33edf1a13ba848601c76b738c423863554..e1bed541742e0ded5d2a0700f7aa228b2839ff16 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
+++ b/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
@@ -112,6 +112,14 @@ namespace Xamarin.Forms.Platform.iOS
                        {
                                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
index cb6449822173b818543a8bdf270375da5827aa4e..6b881cdc19425435e38ba177fc9472412013f3f0 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs
+++ b/Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs
@@ -135,17 +135,21 @@ namespace Xamarin.Forms.Platform.iOS
                        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)