[iOS] Alternative proposal for PR 7794 (#7811)

* emptyview fix

* fix

* added collectionview flag

* added using for List

* fix formatting

* fix formatting 2

* fix formatting 3

* fixes

* fix test

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7758.xaml

@@ -0,0 +1,52 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<controls:TestContentPage  
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    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" 
+    xmlns:controls="clr-namespace:Xamarin.Forms.Controls"
+    mc:Ignorable="d"
+    x:Class="Xamarin.Forms.Controls.Issues.Issue7758">
+    <ContentPage.Resources>
+        <ResourceDictionary>
+            <Style TargetType="StackLayout" x:Key="StackLayoutStyle">
+                <Setter Property="Orientation" Value="Vertical"/>
+                <Setter Property="HorizontalOptions" Value="Center"/>
+                <Setter Property="VerticalOptions" Value="Center"/>
+                <Setter Property="Padding" Value="20, 0"/>
+                <Setter Property="Spacing" Value="10"/>
+                <Setter Property="BackgroundColor" Value="Wheat"/>
+            </Style>
+        </ResourceDictionary>
+    </ContentPage.Resources>
+    <Grid RowSpacing="0">
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto"/>
+            <RowDefinition/>
+            <RowDefinition Height="Auto"/>
+        </Grid.RowDefinitions>
+        
+        <Grid Grid.Row="0" BackgroundColor="Black" Padding="10">
+            <Label Text="If the red line is not between Item 3 and Item 4, the test has failed. Change device orientation to landscape. If the red line is not between Item 3 and Item 4, the test has failed. If there is a visible white background during orientation change, the test has failed." TextColor="White"/>
+        </Grid>
+        
+        <CollectionView Grid.Row="1">
+            <CollectionView.EmptyView>
+                <ContentView HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" BackgroundColor="Beige">
+                    <StackLayout Style="{x:StaticResource StackLayoutStyle}">
+                        <Label Text="Text1" HorizontalTextAlignment="Center" FontAttributes="Bold" FontSize="14.5"/>
+                        <Label Text="Text2" HorizontalTextAlignment="Center" TextColor="#636571" FontSize="14.5"/>
+                        <Label Text="Text3" HorizontalTextAlignment="Center" FontAttributes="Bold" FontSize="14.5"/>
+                        <Label Text="Text4" HorizontalTextAlignment="Center" TextColor="#636571" FontSize="14.5"/>
+                        <Label Text="Text5" HorizontalTextAlignment="Center" FontAttributes="Bold" FontSize="14.5"/>
+                        <Label Text="Text6" HorizontalTextAlignment="Center" TextColor="#636571" FontSize="14.5"/>
+                    </StackLayout>
+                </ContentView>
+            </CollectionView.EmptyView>
+        </CollectionView>
+        
+        <Grid Grid.Row="2" BackgroundColor="Black" HeightRequest="50"/>
+        
+        <Grid Grid.Row="1" BackgroundColor="Red" HeightRequest="5" VerticalOptions="Center"/>
+    </Grid>
+</controls:TestContentPage> 

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7758.xaml.cs

@@ -0,0 +1,25 @@
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 7758, "[iOS] EmptyView is not rendered in screen center", PlatformAffected.iOS)]
+	public partial class Issue7758 : TestContentPage
+	{
+		public Issue7758()
+		{
+#if APP
+			Device.SetFlags(new List<string> { CollectionView.CollectionViewExperimental });
+
+			InitializeComponent();
+#endif
+		}
+
+		protected override void Init()
+		{
+
+		}
+    }
+}

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

@@ -55,6 +55,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue7519Xaml.xaml.cs">
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7758.xaml.cs">
+      <SubType>Code</SubType>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue7593.xaml.cs">
       <SubType>Code</SubType>
     </Compile>
@@ -1418,6 +1421,9 @@
     <Compile Update="$(MSBuildThisFileDirectory)Issue7593.xaml.cs">
       <DependentUpon>Issue7593.xaml</DependentUpon>
     </Compile>
+    <Compile Update="$(MSBuildThisFileDirectory)Issue7758.xaml.cs">
+      <DependentUpon>Issue7758.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue1455.xaml">
@@ -1479,4 +1485,10 @@
       <Generator>MSBuild:Compile</Generator>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue7758.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

Xamarin.Forms.Platform.iOS/CollectionView/ItemsViewController.cs

@@ -140,8 +140,13 @@ namespace Xamarin.Forms.Platform.iOS
 			if (!_initialConstraintsSet)
 			{
 				ItemsViewLayout.ConstrainTo(CollectionView.Bounds.Size);
+				UpdateEmptyView();
 				_initialConstraintsSet = true;
 			}
+			else
+			{
+				ResizeEmptyView();
+			}
 		}
 
 		protected virtual UICollectionViewDelegator CreateDelegator()
@@ -267,6 +272,15 @@ namespace Xamarin.Forms.Platform.iOS
 			UpdateEmptyViewVisibility(ItemsSource?.ItemCount == 0);
 		}
 
+		void ResizeEmptyView()
+		{
+			if (_emptyUIView != null)
+				_emptyUIView.Frame = CollectionView.Frame;
+
+			if (_emptyViewFormsElement != null)
+				_emptyViewFormsElement.Layout(CollectionView.Frame.ToRectangle());
+		}
+
 		protected void UpdateSubview(object view, DataTemplate viewTemplate, ref UIView uiView, ref VisualElement formsElement)
 		{
 			uiView?.RemoveFromSuperview();

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

@@ -97,7 +97,6 @@ namespace Xamarin.Forms.Platform.iOS
 
 			SetNativeControl(ItemsViewController.View);
 			ItemsViewController.CollectionView.BackgroundColor = UIColor.Clear;
-			ItemsViewController.UpdateEmptyView();
 			UpdateHorizontalScrollBarVisibility();
 			UpdateVerticalScrollBarVisibility();