- expander flag

Xamarin.Forms.Controls/CoreGallery.cs

@@ -17,6 +17,7 @@
 using Xamarin.Forms.Controls.GalleryPages.PlatformTestsGallery;
 using Xamarin.Forms.Controls.GalleryPages.TwoPaneViewGalleries;
 using Xamarin.Forms.Controls.GalleryPages.AppThemeGalleries;
+using Xamarin.Forms.Controls.GalleryPages.ExpanderGalleries;
 
 namespace Xamarin.Forms.Controls
 {
@@ -297,7 +298,7 @@ public override string ToString()
 				new GalleryPageFactory(() => new RadioButtonGroupGalleryPage(), "RadioButton group Gallery - Legacy"),
 				new GalleryPageFactory(() => new RadioButtonCoreGalleryPage(), "RadioButton Gallery"),
 				new GalleryPageFactory(() => new FontImageSourceGallery(), "Font ImageSource"),
-				new GalleryPageFactory(() => new ExpanderGallery(), "Expander Gallery"),
+				new GalleryPageFactory(() => new ExpanderGalleries(), "Expander Gallery"),
 				new GalleryPageFactory(() => new IndicatorsSample(), "Indicator Gallery"),
 				new GalleryPageFactory(() => new CarouselViewGallery(), "CarouselView Gallery"),
 				new GalleryPageFactory(() => new CarouselViewCoreGalleryPage(), "CarouselView Core Gallery"),

Xamarin.Forms.Controls/GalleryPages/ExpanderGalleries/ExpanderGalleries.cs

@@ -0,0 +1,45 @@
+namespace Xamarin.Forms.Controls.GalleryPages.ExpanderGalleries
+{
+	public class ExpanderGalleries : ContentPage
+	{
+		public ExpanderGalleries()
+		{
+			var descriptionLabel =
+				   new Label { Text = "Expander Galleries", Margin = new Thickness(2, 2, 2, 2) };
+
+			Title = "Expander Galleries";
+
+			var button = new Button
+			{
+				Text = "Enable Expander",
+				AutomationId = "EnableExpander"
+			};
+			button.Clicked += ButtonClicked;
+
+			Content = new ScrollView
+			{
+				Content = new StackLayout
+				{
+					Children =
+					{
+						descriptionLabel,
+						button,
+						GalleryBuilder.NavButton("Expander Gallery", () =>
+							new ExpanderGallery(), Navigation)
+					}
+				}
+			};
+		}
+
+		void ButtonClicked(object sender, System.EventArgs e)
+		{
+			var button = sender as Button;
+
+			button.Text = "Expander Enabled!";
+			button.TextColor = Color.Black;
+			button.IsEnabled = false;
+
+			Device.SetFlags(new[] { ExperimentalFlags.ExpanderExperimental });
+		}
+	}
+}

Xamarin.Forms.Controls/GalleryPages/ExpanderGallery.xaml → Xamarin.Forms.Controls/GalleryPages/ExpanderGalleries/ExpanderGallery.xaml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-             x:Class="Xamarin.Forms.Controls.ExpanderGallery"
+             x:Class="Xamarin.Forms.Controls.GalleryPages.ExpanderGalleries.ExpanderGallery"
              x:Name="page">
     <ScrollView Padding="30, 20">
         <StackLayout BindableLayout.ItemsSource="{Binding Path=Items, Source={x:Reference page}}">

Xamarin.Forms.Controls/GalleryPages/ExpanderGallery.xaml.cs → Xamarin.Forms.Controls/GalleryPages/ExpanderGalleries/ExpanderGallery.xaml.cs

@@ -5,7 +5,7 @@
 using System.Windows.Input;
 using Xamarin.Forms;
 
-namespace Xamarin.Forms.Controls
+namespace Xamarin.Forms.Controls.GalleryPages.ExpanderGalleries
 {
 	public partial class ExpanderGallery : ContentPage
 	{

Xamarin.Forms.Core/Expander.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.CompilerServices;
 using System.Windows.Input;
 using static System.Math;
 
@@ -51,6 +52,7 @@ public class Expander : TemplatedView
 		double _endHeight;
 		bool _shouldIgnoreContentSetting;
 		bool _shouldIgnoreAnimation;
+		static bool isExperimentalFlagSet = false;
 
 		public Expander()
 		{
@@ -59,6 +61,22 @@ public Expander()
 			InternalChildren.Add(ExpanderLayout);
 		}
 
+		internal static void VerifyExperimental([CallerMemberName] string memberName = "", string constructorHint = null)
+		{
+			if (isExperimentalFlagSet)
+				return;
+
+			ExperimentalFlags.VerifyFlagEnabled(nameof(Markup), ExperimentalFlags.ExpanderExperimental, constructorHint, memberName);
+
+			isExperimentalFlagSet = true;
+		}
+
+		protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
+		{			
+			VerifyExperimental();
+			return base.OnMeasure(widthConstraint, heightConstraint);
+		}
+
 		StackLayout ExpanderLayout { get; }
 
 		public double Spacing

Xamarin.Forms.Core/ExperimentalFlags.cs

@@ -17,6 +17,7 @@ internal static class ExperimentalFlags
 		internal const string MediaElementExperimental = "MediaElement_Experimental";
 		internal const string MarkupExperimental = "Markup_Experimental";
 		internal const string AppThemeExperimental = "AppTheme_Experimental";
+		internal const string ExpanderExperimental = "Expander_Experimental";
 
 		[EditorBrowsable(EditorBrowsableState.Never)]
 		public static void VerifyFlagEnabled(