[iOS] Fix crash when going from empty to having items (#5430)

* Fix crash on iOS when going from empty to having items

* Temporarily patching EditorRenderer so iOS tests can run

diff --git a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/EmptyViewGalleries/EmptyViewLoadSimulateGallery.xaml.cs b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/EmptyViewGalleries/EmptyViewLoadSimulateGallery.xaml.cs
index 066abd6..839cc8c 100644 (file)
--- a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/EmptyViewGalleries/EmptyViewLoadSimulateGallery.xaml.cs
+++ b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/EmptyViewGalleries/EmptyViewLoadSimulateGallery.xaml.cs
@@ -1,4 +1,5 @@
-using System.Threading;
+using System.Collections.Generic;
+using System.Threading;
 using Xamarin.Forms.Xaml;
 
 namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.EmptyViewGalleries
@@ -17,6 +18,8 @@ namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.EmptyViewG
                        new Thread(() =>
                        {
                                Thread.Sleep(1000);
+                               Device.BeginInvokeOnMainThread(() => CollectionView.ItemsSource = new List<object>());
+                               Thread.Sleep(1000);
                                Device.BeginInvokeOnMainThread(() => CollectionView.ItemsSource = _demoFilteredItemSource.Items);
                        }).Start();
                }

diff --git a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/ExampleTemplates.cs b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/ExampleTemplates.cs
index e884f5c..6707c68 100644 (file)
--- a/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/ExampleTemplates.cs
+++ b/Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/ExampleTemplates.cs
@@ -20,7 +20,8 @@ namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries
                                {
                                        HeightRequest = 100, WidthRequest = 100,
                                        HorizontalOptions = LayoutOptions.Center,
-                                       VerticalOptions = LayoutOptions.Center
+                                       VerticalOptions = LayoutOptions.Center,
+                                       AutomationId = "photo"
                                };
 
                                image.SetBinding(Image.SourceProperty, new Binding("Image"));

diff --git a/Xamarin.Forms.Core.UITests.Shared/Tests/CollectionViewUITests.cs b/Xamarin.Forms.Core.UITests.Shared/Tests/CollectionViewUITests.cs
index 31df17e..2edb46c 100644 (file)
--- a/Xamarin.Forms.Core.UITests.Shared/Tests/CollectionViewUITests.cs
+++ b/Xamarin.Forms.Core.UITests.Shared/Tests/CollectionViewUITests.cs
@@ -279,5 +279,16 @@ namespace Xamarin.Forms.Core.UITests
                                }
                        }
                }
-       }
+
+        [TestCase("EmptyView", "EmptyView (load simulation)", "photo")]
+        public void VisitAndCheckItem(string collectionTestName, string subgallery, string item)
+        {
+            VisitInitialGallery(collectionTestName);
+
+            App.WaitForElement(t => t.Marked(subgallery));
+            App.Tap(t => t.Marked(subgallery));
+
+            App.WaitForElement(t => t.Marked(item));
+        }
+    }
 }
\ No newline at end of file

diff --git a/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs b/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
index 8b52736..7b9b502 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
+++ b/Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Foundation;
 using UIKit;
 
@@ -12,6 +13,7 @@ namespace Xamarin.Forms.Platform.iOS
                readonly ItemsView _itemsView;
                ItemsViewLayout _layout;
                bool _initialConstraintsSet;
+               bool _safeForReload;
                bool _wasEmpty;
                bool _currentBackgroundIsEmptyView;
 
@@ -25,6 +27,10 @@ namespace Xamarin.Forms.Platform.iOS
                {
                        _itemsView = itemsView;
                        _itemsSource = ItemsSourceFactory.Create(_itemsView.ItemsSource, CollectionView);
+                       
+                       // If we already have data, the UICollectionView will have items and we'll be safe to call
+                       // ReloadData if the ItemsSource changes in the future (see UpdateItemsSource for more).
+                       _safeForReload = _itemsSource?.Count > 0;
 
                        UpdateLayout(layout);
                }
@@ -113,11 +119,59 @@ namespace Xamarin.Forms.Platform.iOS
 
                public virtual void UpdateItemsSource()
                {
-                       _itemsSource =  ItemsSourceFactory.Create(_itemsView.ItemsSource, CollectionView);
+                       if (_safeForReload)
+                       {
+                               UpdateItemsSourceAndReload();
+                       }
+                       else
+                       {
+                               // Okay, thus far this UICollectionView has never had any items in it. At this point, if
+                               // we set the ItemsSource and try to call ReloadData(), it'll crash. AFAICT this is a bug, but
+                               // until it's fixed (or we can figure out another way to go from empty -> having items), we'll
+                               // have to use this crazy workaround
+                               EmptyCollectionViewReloadWorkaround();
+                       }
+               }
+
+               void UpdateItemsSourceAndReload()
+               {
+                       _itemsSource = ItemsSourceFactory.Create(_itemsView.ItemsSource, CollectionView);
                        CollectionView.ReloadData();
                        CollectionView.CollectionViewLayout.InvalidateLayout();
                }
 
+               void EmptyCollectionViewReloadWorkaround()
+               {
+                       var enumerator = _itemsView.ItemsSource.GetEnumerator();
+
+                       if (!enumerator.MoveNext())
+                       {
+                               // The source we're updating to is empty, so we can just update as normal; it won't crash
+                               UpdateItemsSourceAndReload();
+                       }
+                       else
+                       {
+                               // Grab the first item from the new ItemsSource and create a usable source for the UICollectionView
+                               // from that
+                               var firstItem = new List<object> { enumerator.Current };
+                               _itemsSource = ItemsSourceFactory.Create(firstItem, CollectionView);
+
+                               // Insert that item into the UICollectionView
+                               // TODO ezhart When we implement grouping, this will need to be the index of the first actual item
+                               // Which might not be zero,zero if we have empty groups
+                               var indexesToInsert = new NSIndexPath[1] { NSIndexPath.Create(0, 0) };
+
+                               UIView.PerformWithoutAnimation(() =>
+                               {
+                                       CollectionView.InsertItems(indexesToInsert);
+                               });
+
+                               // Okay, from now on we can just call ReloadData and things will work fine
+                               _safeForReload = true;
+                               UpdateItemsSource();
+                       }
+               }
+
                protected virtual void UpdateDefaultCell(DefaultCell cell, NSIndexPath indexPath)
                {
                        cell.Label.Text = _itemsSource[indexPath.Row].ToString();

diff --git a/Xamarin.Forms.Platform.iOS/Renderers/EditorRenderer.cs b/Xamarin.Forms.Platform.iOS/Renderers/EditorRenderer.cs
index e14d888..5433328 100644 (file)
--- a/Xamarin.Forms.Platform.iOS/Renderers/EditorRenderer.cs
+++ b/Xamarin.Forms.Platform.iOS/Renderers/EditorRenderer.cs
@@ -60,7 +60,7 @@ namespace Xamarin.Forms.Platform.iOS
                {
                        _placeholderLabel.Text = Element.Placeholder;
                }
-
+               
                protected internal override void UpdatePlaceholderColor()
                {
                        if (Element.PlaceholderColor == Color.Default)