Fix disappearing MasterDetail menu on UWP (#5808)

* Ensure Mstrdetail Popover menu is always visible

For #5412

* Add UITest for Issue 5412

* Add missing namespace

* Update Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5412.cs

Co-Authored-By: mrlacey <matt@mrlacey.co.uk>
fixes #5412
fixes #5637

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5412.cs

@@ -0,0 +1,123 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using NUnit.Framework;
+using Xamarin.UITest;
+using Xamarin.UITest.iOS;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(Core.UITests.UITestCategories.MasterDetailPage)]
+	[Category(Core.UITests.UITestCategories.Navigation)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 5412, "5412 - (NavigationBar disappears on MasterDetailPage)", PlatformAffected.UWP)]
+	public class Issue5412 : TestContentPage
+	{
+		protected override async void Init()
+		{
+			await Navigation.PushModalAsync(new Issue5412MainPage());
+		}
+
+#if UITEST && __WINDOWS__
+		[Test]
+		public void Issue5412Test()
+		{
+			var hamburgerText = "\uE700";
+			var settings = "Settings";
+			var back = "Back";
+		
+			RunningApp.WaitForElement(hamburgerText);
+			RunningApp.Tap(hamburgerText);
+
+			RunningApp.WaitForElement(settings);
+			RunningApp.Tap(settings);
+
+			RunningApp.WaitForElement(back);
+			RunningApp.Tap(back);
+
+			// This fails if the menu isn't displayed (original error behavior)
+			RunningApp.WaitForElement(hamburgerText);
+		}
+#endif
+	}
+
+	public class Issue5412MainPage : MasterDetailPage
+	{
+		public Issue5412MainPage()
+		{
+			var menuBtn = new Button
+			{
+				Text = "Settings"
+			};
+			menuBtn.Clicked += (sender, e) =>
+			{
+				var mdp = ((sender as Button).Parent.Parent as MasterDetailPage);
+				mdp.Detail.Navigation.PushAsync(new Issue5412SettingPage());
+				mdp.IsPresented = false;
+			};
+
+			MasterBehavior = MasterBehavior.Popover;
+			Master = new ContentPage
+			{
+				Content = menuBtn,
+				Title = "Menu title"
+			};
+			Detail = new NavigationPage(new Issue5412IndexPage());
+		}
+	}
+
+	public class Issue5412SettingPage : ContentPage
+	{
+		public Issue5412SettingPage()
+		{
+			Content = new StackLayout
+			{
+				HorizontalOptions = LayoutOptions.CenterAndExpand,
+				VerticalOptions = LayoutOptions.CenterAndExpand,
+				Children = {
+					new Label
+					{
+						Text = "Settings Page",
+						FontSize = Device.GetNamedSize (NamedSize.Large, typeof(Label))
+					},
+					new Label
+					{
+						Text = "Navigate back and check the navbar & menu are still visible.",
+						FontSize = Device.GetNamedSize (NamedSize.Medium, typeof(Label))
+					},
+				}
+			};
+		}
+	};
+
+	public class Issue5412IndexPage : ContentPage
+	{
+		public Issue5412IndexPage()
+		{
+			Content = new StackLayout
+			{
+				HorizontalOptions = LayoutOptions.CenterAndExpand,
+				VerticalOptions = LayoutOptions.CenterAndExpand,
+				Children = {
+					new Label
+					{
+						Text = "Index Page",
+						FontSize = Device.GetNamedSize (NamedSize.Large, typeof(Label))
+					},
+					new Label
+					{
+						Text = "Open the hamburger menu and navigate to settings page",
+						FontSize = Device.GetNamedSize (NamedSize.Medium, typeof(Label))
+					},
+				}
+			};
+		}
+	}
+}

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

@@ -9,6 +9,7 @@
     <Import_RootNamespace>Xamarin.Forms.Controls.Issues</Import_RootNamespace>
   </PropertyGroup>
   <ItemGroup>
+    <Compile Include="$(MSBuildThisFileDirectory)Issue5412.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Helpers\GarbageCollectionHelper.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue4879.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue5555.cs" />

Xamarin.Forms.Platform.UAP/MasterDetailPageRenderer.cs

@@ -335,7 +335,7 @@ namespace Xamarin.Forms.Platform.UWP
 				return;
 
 			Control.DetailTitle = GetCurrentPage().Title ?? Element?.Title;
-			(this as ITitleProvider).ShowTitle = !string.IsNullOrEmpty(Control.DetailTitle);
+			(this as ITitleProvider).ShowTitle = !string.IsNullOrEmpty(Control.DetailTitle) || Element.MasterBehavior == MasterBehavior.Popover;
 		}
 
 		async void UpdateDetailTitleIcon()