[Android] CarouselView position resets when visibility toggled

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12848.xaml

@@ -0,0 +1,42 @@
+<?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:controls="clr-namespace:Xamarin.Forms.Controls"
+    x:Class="Xamarin.Forms.Controls.Issues.Issue12848"
+    Title="Issue 12848">
+    <StackLayout>
+        <Label
+            Padding="12"
+            BackgroundColor="Black"
+            TextColor="White"
+            Text="Swipe the CarouselView to select the item numbered 2. Then, tap the Hide Button to hide the Carousel and the Show Button to show the Carousel again. If the position of the Carousel is the same as before hiding, the test has passed."/>
+        <CarouselView
+            AutomationId="TestCarouselView"
+            x:Name="carousel"
+            HorizontalOptions="Center"
+            ItemsSource="{Binding}">
+            <CarouselView.ItemTemplate>
+                <DataTemplate>
+                    <Label
+                        Text="{Binding}"
+                        FontSize="96"
+                        HorizontalTextAlignment="Center"/>
+                </DataTemplate>
+            </CarouselView.ItemTemplate>
+        </CarouselView>
+        <Label
+           AutomationId="CarouselPosition"
+            Text="{Binding Source={x:Reference carousel}, Path=Position}"
+            HorizontalOptions="Center"/>
+        <Button
+            AutomationId="HideButton"
+            Text="Hide CarouselView"
+            Clicked="OnHideButtonClicked"/>
+        <Button
+            AutomationId="ShowButton"
+            Text="Show CarouselView"
+            Clicked="OnShowButtonClicked"/>
+    </StackLayout>
+</controls:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue12848.xaml.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 12848, "[Bug] CarouselView position resets when visibility toggled",
+		PlatformAffected.Android)]
+	public partial class Issue12848 : TestContentPage
+	{
+		protected override void Init()
+		{
+#if APP
+			InitializeComponent();
+
+			BindingContext = new List<int> { 1, 2, 3 };
+#endif
+		}
+
+#if APP
+		void OnShowButtonClicked(object sender, EventArgs e)
+		{
+			carousel.IsVisible = true;
+		}
+
+		void OnHideButtonClicked(object sender, EventArgs e)
+		{
+			carousel.IsVisible = false;
+		}
+#endif
+
+#if UITEST
+		[Test]
+		public void Issue12848Test()
+		{
+			RunningApp.WaitForElement("TestCarouselView");
+			RunningApp.SwipeRightToLeft();
+			Assert.AreEqual(1, int.Parse(RunningApp.Query(q => q.Marked("CarouselPosition"))[0].Text));
+			RunningApp.Tap("HideButton");
+			RunningApp.Tap("ShowButton");
+			Assert.AreEqual(1, int.Parse(RunningApp.Query(q => q.Marked("CarouselPosition"))[0].Text));
+			RunningApp.Screenshot("Test passed");
+		}
+#endif
+	}
+}

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

@@ -1682,6 +1682,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue12777.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11911.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11691.xaml.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue12848.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12315.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12912.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue12910.xaml.cs" />
@@ -2059,6 +2060,9 @@
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue11691.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue12848.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue12315.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>

Xamarin.Forms.Platform.Android/CollectionView/CarouselViewRenderer.cs

@@ -334,21 +334,21 @@ void UpdateItemDecoration()
 
 		void UpdateInitialPosition()
 		{
-			int position = 0;
 			int itemCount = 0;
+			int position;
 
 			if (Carousel.CurrentItem != null)
 			{
 				var carouselEnumerator = Carousel.ItemsSource.GetEnumerator();
+				var items = new List<object>();
 
 				while (carouselEnumerator.MoveNext())
 				{
-					if (carouselEnumerator.Current == Carousel.CurrentItem)
-						position = itemCount;
-
+					items.Add(carouselEnumerator.Current);
 					itemCount++;
 				}
 
+				position = items.IndexOf(Carousel.CurrentItem);
 				Carousel.Position = position;
 			}
 			else