[CollectionView] UWP- Updating the ItemsLayout type should refresh the layout

Xamarin.Forms.Platform.UAP/CollectionView/ItemContentControl.cs

@@ -9,6 +9,7 @@ namespace Xamarin.Forms.Platform.UWP
 {
 	public class ItemContentControl : ContentControl
 	{
+		View _view;
 		IVisualElementRenderer _renderer;
 
 		public ItemContentControl()
@@ -17,7 +18,7 @@ public ItemContentControl()
 		}
 
 		public static readonly DependencyProperty FormsDataTemplateProperty = DependencyProperty.Register(
-			nameof(FormsDataTemplate), typeof(DataTemplate), typeof(ItemContentControl), 
+			nameof(FormsDataTemplate), typeof(DataTemplate), typeof(ItemContentControl),
 			new PropertyMetadata(default(DataTemplate), FormsDataTemplateChanged));
 
 		static void FormsDataTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
@@ -38,7 +39,7 @@ public DataTemplate FormsDataTemplate
 		}
 
 		public static readonly DependencyProperty FormsDataContextProperty = DependencyProperty.Register(
-			nameof(FormsDataContext), typeof(object), typeof(ItemContentControl), 
+			nameof(FormsDataContext), typeof(object), typeof(ItemContentControl),
 			new PropertyMetadata(default(object), FormsDataContextChanged));
 
 		static void FormsDataContextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
@@ -103,15 +104,11 @@ protected override void OnContentChanged(object oldContent, object newContent)
 		{
 			base.OnContentChanged(oldContent, newContent);
 
-			if (oldContent is FrameworkElement oldElement)
-			{
-				oldElement.Loaded -= ContentLoaded;
-			}
+			if (oldContent != null && _view != null)
+				_view.MeasureInvalidated -= OnViewMeasureInvalidated;
 
-			if (newContent is FrameworkElement newElement)
-			{
-				newElement.Loaded += ContentLoaded;
-			}
+			if (newContent != null && _view != null)
+				_view.MeasureInvalidated += OnViewMeasureInvalidated;
 		}
 
 		internal void Realize()
@@ -132,17 +129,17 @@ internal void Realize()
 				return;
 			}
 
-			var view = FormsDataTemplate.CreateContent(dataContext, container) as View;
-			view.BindingContext = dataContext;
-			_renderer = Platform.CreateRenderer(view);
-			Platform.SetRenderer(view, _renderer);
+			_view = FormsDataTemplate.CreateContent(dataContext, container) as View;
+			_view.BindingContext = dataContext;
+			_renderer = Platform.CreateRenderer(_view);
+			Platform.SetRenderer(_view, _renderer);
 
 			Content = _renderer.ContainerElement;
 
-			itemsView?.AddLogicalChild(view);
+			itemsView?.AddLogicalChild(_view);
 		}
 
-		void ContentLoaded(object sender, RoutedEventArgs e)
+		void OnViewMeasureInvalidated(object sender, EventArgs e)
 		{
 			InvalidateMeasure();
 		}

Xamarin.Forms.Platform.UAP/CollectionView/ItemsViewRenderer.cs

@@ -1,15 +1,16 @@
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Threading.Tasks;
+
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Data;
-using Windows.UI.Xaml.Controls.Primitives;
-using Windows.Foundation;
+
 using Xamarin.Forms.Internals;
+
+using UwpApp = Windows.UI.Xaml.Application;
+using UwpDataTemplate = Windows.UI.Xaml.DataTemplate;
 using UwpScrollBarVisibility = Windows.UI.Xaml.Controls.ScrollBarVisibility;
-using UWPApp = Windows.UI.Xaml.Application;
-using UWPDataTemplate = Windows.UI.Xaml.DataTemplate;
 
 namespace Xamarin.Forms.Platform.UWP
 {
@@ -27,8 +28,8 @@ public abstract class ItemsViewRenderer<TItemsView> : ViewRenderer<TItemsView, L
 		internal double _previousVerticalOffset;
 
 		protected ListViewBase ListViewBase { get; private set; }
-		protected UWPDataTemplate ViewTemplate => (UWPDataTemplate)UWPApp.Current.Resources["View"];
-		protected UWPDataTemplate ItemsViewTemplate => (UWPDataTemplate)UWPApp.Current.Resources["ItemsViewDefaultTemplate"];
+		protected UwpDataTemplate ViewTemplate => (UwpDataTemplate)UwpApp.Current.Resources["View"];
+		protected UwpDataTemplate ItemsViewTemplate => (UwpDataTemplate)UwpApp.Current.Resources["ItemsViewDefaultTemplate"];
 
 		protected ItemsViewRenderer()
 		{
@@ -392,6 +393,31 @@ protected virtual void UpdateEmptyView()
 			UpdateEmptyViewVisibility();
 		}
 
+		protected virtual void UpdateItemsLayout()
+		{
+			if (_scrollViewer != null)
+				_scrollViewer.ViewChanged -= OnScrollViewChanged;
+
+			if (ListViewBase != null)
+			{
+				ListViewBase.ItemsSource = null;
+				ListViewBase = null;
+			}
+
+			ListViewBase = SelectListViewBase();
+			ListViewBase.IsSynchronizedWithCurrentItem = false;
+
+			FindScrollViewer(ListViewBase);
+
+			SetNativeControl(ListViewBase);
+
+			UpdateItemTemplate();
+			UpdateItemsSource();
+			UpdateVerticalScrollBarVisibility();
+			UpdateHorizontalScrollBarVisibility();
+			UpdateEmptyView();
+		}
+
 		FrameworkElement RealizeEmptyViewTemplate(object bindingContext, DataTemplate emptyViewTemplate)
 		{
 			if (emptyViewTemplate == null)
@@ -478,4 +504,4 @@ void OnScrollViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
 			HandleScroll(_scrollViewer);
 		}
 	}
-}
+}

Xamarin.Forms.Platform.UAP/CollectionView/StructuredItemsViewRenderer.cs

@@ -1,6 +1,8 @@
 using System;
 using System.ComponentModel;
+
 using Windows.UI.Xaml.Controls;
+
 using UWPApp = Windows.UI.Xaml.Application;
 using WListView = Windows.UI.Xaml.Controls.ListView;
 using WScrollMode = Windows.UI.Xaml.Controls.ScrollMode;
@@ -43,6 +45,10 @@ protected override void OnElementPropertyChanged(object sender, PropertyChangedE
 			{
 				UpdateFooter();
 			}
+			else if (changedProperty.Is(StructuredItemsView.ItemsLayoutProperty))
+			{
+				UpdateItemsLayout();
+			}
 		}
 
 		protected override ListViewBase SelectListViewBase()
@@ -57,7 +63,7 @@ protected override ListViewBase SelectListViewBase()
 					return CreateHorizontalListView(listItemsLayout);
 			}
 
-			throw new NotImplementedException("The layout is not implemented");			
+			throw new NotImplementedException("The layout is not implemented");
 		}
 
 		protected virtual void UpdateHeader()
@@ -211,7 +217,7 @@ static ListViewBase CreateVerticalListView(LinearItemsLayout listItemsLayout)
 
 		static ListViewBase CreateHorizontalListView(LinearItemsLayout listItemsLayout)
 		{
-			var horizontalListView = new WListView()
+			var horizontalListView = new FormsListView()
 			{
 				ItemsPanel = (ItemsPanelTemplate)UWPApp.Current.Resources["HorizontalListItemsPanel"],
 				ItemContainerStyle = GetHorizontalItemContainerStyle(listItemsLayout)
@@ -238,8 +244,8 @@ static WStyle GetItemContainerStyle(GridItemsLayout layout)
 		static WStyle GetVerticalItemContainerStyle(LinearItemsLayout layout)
 		{
 			var v = layout?.ItemSpacing ?? 0;
-			var margin = new WThickness(0, v, 0, v);	
-			
+			var margin = new WThickness(0, v, 0, v);
+
 			var style = new WStyle(typeof(ListViewItem));
 			style.Setters.Add(new WSetter(ListViewItem.MarginProperty, margin));
 			return style;