Fix issue changing the ItemsLayout in UWP CollectionView (#13470) fixes #13437

Co-authored-by: E.Z. Hart <hartez@users.noreply.github.com>

Author: jsuarezruiz

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue13437.xaml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<controls:TestContentPage
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:controls="clr-namespace:Xamarin.Forms.Controls"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:d="http://xamarin.com/schemas/2014/forms/design"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    x:Class="Xamarin.Forms.Controls.Issues.Issue13437"
+    Title="Issue 13437">
+    <ContentPage.Content>
+        <StackLayout>
+            <Label
+                Padding="12"
+                BackgroundColor="Black"
+                TextColor="White"
+                Text="Tap each Button to change the CollectionView ItemsLayout. If in all cases, the ItemsLayout changes correctly, the test has passed."/>
+            <Button x:Name="ButtonOne"/>
+            <Button x:Name="ButtonTwo"/>
+            <Button x:Name="ButtonThree"/>
+            <Button x:Name="ButtonFour"/>
+            <CollectionView 
+                x:Name="Collection"
+                ItemsSource="{Binding Items}">
+                <CollectionView.ItemTemplate>
+                    <DataTemplate>
+                        <Label 
+                            Text="{Binding Text}"
+                            WidthRequest="100"/>
+                    </DataTemplate>
+                </CollectionView.ItemTemplate>
+            </CollectionView>
+        </StackLayout>
+    </ContentPage.Content>
+</controls:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue13437.xaml.cs

@@ -0,0 +1,95 @@
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using System.Collections.ObjectModel;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Issue(IssueTracker.Github, 13437, "[Bug] Changing ItemsLayout of CollectionView at runtime does not work on UWP",
+		PlatformAffected.UWP)]
+	public partial class Issue13437 : TestContentPage
+	{
+		public Issue13437()
+		{
+#if APP
+			InitializeComponent();
+
+			ButtonOne.Text = "Set Vertical List";
+			ButtonOne.Command = new Command(() =>
+			{
+				SetVerticalList();
+			});
+
+			ButtonTwo.Text = "Set Horizontal List";
+			ButtonTwo.Command = new Command(() =>
+			{
+				SetHorizontalList();
+			});
+
+			ButtonThree.Text = "Set Grid 2 List";
+			ButtonThree.Command = new Command(() =>
+			{
+				SetTwoGrid();
+			});
+
+			ButtonFour.Text = "Set Grid 3 List";
+			ButtonFour.Command = new Command(() =>
+			{
+				SetThreeGrid();
+			});
+
+			var collection = new ObservableCollection<Issue13437Model>();
+
+			for (int i = 0; i < 42; i++)
+			{
+				collection.Add(new Issue13437Model { Text = "Label " + i.ToString() });
+			}
+
+			Collection.ItemsSource = collection;
+
+			BindingContext = new ViewModel10482();
+#endif
+		}
+
+		protected override void Init()
+		{
+
+		}
+#if APP
+		void SetVerticalList()
+		{
+			Collection.ItemsLayout = new LinearItemsLayout(ItemsLayoutOrientation.Vertical);
+		}
+
+		void SetHorizontalList()
+		{
+			Collection.ItemsLayout = new LinearItemsLayout(ItemsLayoutOrientation.Horizontal);
+		}
+
+		void SetTwoGrid()
+		{
+			Collection.ItemsLayout = new GridItemsLayout(ItemsLayoutOrientation.Vertical)	
+			{
+					Span = 2,
+					HorizontalItemSpacing = 5,
+					VerticalItemSpacing = 5
+			};
+		}
+
+		void SetThreeGrid()
+		{
+			Collection.ItemsLayout = new GridItemsLayout(3, ItemsLayoutOrientation.Vertical);
+		}
+#endif
+	}
+
+	public class Issue13437Model
+	{
+		public string Text { get; set; }
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -12,6 +12,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)CollectionViewGroupTypeIssue.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11214.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue13109.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue13437.xaml.cs">
+      <DependentUpon>Issue13437.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue13126.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue13126_2.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue13551.cs" />
@@ -2665,6 +2668,10 @@
     </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue13437.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)VisualGallery.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>

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

@@ -78,6 +78,8 @@ void FindItemsWrapGrid()
 
 			_wrapGrid.SizeChanged -= WrapGridSizeChanged;
 			_wrapGrid.SizeChanged += WrapGridSizeChanged;
+
+			UpdateItemSize();
 		}
 
 		void WrapGridSizeChanged(object sender, SizeChangedEventArgs e)

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

@@ -418,6 +418,9 @@ protected virtual void UpdateItemsLayout()
 
 			SetNativeControl(ListViewBase);
 
+			_defaultHorizontalScrollVisibility = null;
+			_defaultVerticalScrollVisibility = null;
+
 			UpdateItemTemplate();
 			UpdateItemsSource();
 			UpdateVerticalScrollBarVisibility();