[Android] Fix previewer exceptions with shell (#5955)

* shell preivewer

* nonappcompat hack

* - moove up null check

* internal IsDesignerContext

Xamarin.Forms.Platform.Android/AppCompat/CarouselPageRenderer.cs

@@ -101,7 +101,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 		{
 			base.OnElementChanged(e);
 
-			var activity = (FormsAppCompatActivity)Context;
+			var activity = (FormsAppCompatActivity)Context.GetActivity();
 
 			if (e.OldElement != null)
 				((IPageController)e.OldElement).InternalChildren.CollectionChanged -= OnChildrenCollectionChanged;

Xamarin.Forms.Platform.Android/AppCompat/MasterDetailContainer.cs

@@ -26,7 +26,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 
 		public bool MarkedForDispose { get; internal set; } = false;
 
-		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = ((FormsAppCompatActivity)Context).SupportFragmentManager);
+		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = Context.GetFragmentManager());
 
 		protected override void OnLayout(bool changed, int l, int t, int r, int b)
 		{

Xamarin.Forms.Platform.Android/AppCompat/NavigationPageRenderer.cs

@@ -88,7 +88,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 			{
 				if (_platform == null)
 				{
-					if (Context is FormsAppCompatActivity activity)
+					if (Context.GetActivity() is FormsAppCompatActivity activity)
 					{
 						_platform = activity.Platform;
 					}
@@ -122,7 +122,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 			}
 		}
 
-		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = ((FormsAppCompatActivity)Context).SupportFragmentManager);
+		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = Context.GetFragmentManager());
 
 		IPageController PageController => Element;
 
@@ -745,7 +745,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 		void SetupToolbar()
 		{
 			Context context = Context;
-			var activity = (FormsAppCompatActivity)context;
+			var activity = context.GetActivity();
 
 			AToolbar bar;
 			if (FormsAppCompatActivity.ToolbarResource != 0)
@@ -935,7 +935,6 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 				return;
 
 			Context context = Context;
-			var activity = (FormsAppCompatActivity)context;
 			AToolbar bar = _toolbar;
 			ActionBarDrawerToggle toggle = _drawerToggle;
 
@@ -954,8 +953,9 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 					toggle.SyncState();
 				}
 
-				if (NavigationPage.GetHasBackButton(currentPage))
+				if (NavigationPage.GetHasBackButton(currentPage) && !Context.IsDesignerContext())
 				{
+					var activity = (global::Android.Support.V7.App.AppCompatActivity)context.GetActivity();
 					var icon = new DrawerArrowDrawable(activity.SupportActionBar.ThemedContext);
 					icon.Progress = 1;
 					bar.NavigationIcon = icon;

Xamarin.Forms.Platform.Android/AppCompat/Platform.cs

@@ -369,8 +369,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 
 		void LayoutRootPage(Page page, int width, int height)
 		{
-			var activity = (FormsAppCompatActivity)_context;
-			page.Layout(new Rectangle(0, 0, activity.FromPixels(width), activity.FromPixels(height)));
+			page.Layout(new Rectangle(0, 0, _context.FromPixels(width), _context.FromPixels(height)));
 		}
 
 		Task PresentModal(Page modal, bool animated)
@@ -457,9 +456,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 			{
 				if (changed)
 				{
-					var activity = (FormsAppCompatActivity)Context;
-
-					_modal.Layout(new Rectangle(0, 0, activity.FromPixels(r - l), activity.FromPixels(b - t)));
+					_modal.Layout(new Rectangle(0, 0, Context.FromPixels(r - l), Context.FromPixels(b - t)));
 					_backgroundView.Layout(0, 0, r - l, b - t);
 				}
 

Xamarin.Forms.Platform.Android/AppCompat/TabbedPageRenderer.cs

@@ -73,7 +73,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 			}
 		}
 
-		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = ((FormsAppCompatActivity)Context).SupportFragmentManager);
+		FragmentManager FragmentManager => _fragmentManager ?? (_fragmentManager = Context.GetFragmentManager());
 		bool IsBottomTabPlacement => (Element != null) ? Element.OnThisPlatform().GetToolbarPlacement() == ToolbarPlacement.Bottom : false;
 
 		public Color BarItemColor
@@ -231,7 +231,7 @@ namespace Xamarin.Forms.Platform.Android.AppCompat
 		{
 			base.OnElementChanged(e);
 
-			var activity = (FormsAppCompatActivity)Context;
+			var activity = Context.GetActivity();
 
 			if (e.OldElement != null)
 				((IPageController)e.OldElement).InternalChildren.CollectionChanged -= OnChildrenCollectionChanged;

Xamarin.Forms.Platform.Android/ContextExtensions.cs

@@ -5,6 +5,7 @@ using Android.Util;
 using Android.Views.InputMethods;
 using AApplicationInfoFlags = Android.Content.PM.ApplicationInfoFlags;
 using AActivity = Android.App.Activity;
+using AFragmentManager = Android.Support.V4.App.FragmentManager;
 
 namespace Xamarin.Forms.Platform.Android
 {
@@ -96,5 +97,49 @@ namespace Xamarin.Forms.Platform.Android
 
 			return null;
 		}
+
+		internal static Context GetThemedContext(this Context context)
+		{
+			if (context == null)
+				return null;
+
+			if (context.IsDesignerContext())
+				return context;
+
+			if (context is global::Android.Support.V7.App.AppCompatActivity activity)
+				return activity.SupportActionBar.ThemedContext;
+
+			if (context is ContextWrapper contextWrapper)
+				return contextWrapper.BaseContext.GetThemedContext();
+
+			return null;
+		}
+
+		internal static bool IsDesignerContext(this Context context)
+		{
+			if (context == null)
+				return false;
+			
+			if ($"{context.ToString()}".Contains("com.android.layoutlib.bridge.android.BridgeContext"))
+				return true;
+
+			if (context is ContextWrapper contextWrapper)
+				return contextWrapper.BaseContext.IsDesignerContext();
+
+			return false;
+		}
+
+		public static AFragmentManager GetFragmentManager(this Context context)
+		{
+			if (context == null)
+				return null;
+
+			var activity = context.GetActivity();
+
+			if (activity is global::Android.Support.V4.App.FragmentActivity fa)
+				return fa.SupportFragmentManager;
+
+			return null;
+		}
 	}
 }

Xamarin.Forms.Platform.Android/Renderers/ContainerView.cs

@@ -50,7 +50,7 @@ namespace Xamarin.Forms.Platform.Android
 
 			if (disposing)
 			{
-				_renderer.Dispose();
+				_renderer?.Dispose();
 				_renderer = null;
 				_view = null;
 				_context = null;

Xamarin.Forms.Platform.Android/Renderers/ShellFlyoutTemplatedContentRenderer.cs

@@ -38,13 +38,48 @@ namespace Xamarin.Forms.Platform.Android
         protected virtual void LoadView(IShellContext shellContext)
         {
             var context = shellContext.AndroidContext;
-            var coordinator = LayoutInflater.FromContext(context).Inflate(Resource.Layout.FlyoutContent, null);
-            var recycler = coordinator.FindViewById<RecyclerView>(Resource.Id.flyoutcontent_recycler);
-            var appBar = coordinator.FindViewById<AppBarLayout>(Resource.Id.flyoutcontent_appbar);
+            var coordinator = (ViewGroup)LayoutInflater.FromContext(context).Inflate(Resource.Layout.FlyoutContent, null);
+			var recycler = coordinator.FindViewById<RecyclerView>(Resource.Id.flyoutcontent_recycler);
+			var appBar = coordinator.FindViewById<ViewGroup>(Resource.Id.flyoutcontent_appbar);
 
-            _rootView = coordinator;
+			_rootView = coordinator;
 
-            appBar.AddOnOffsetChangedListener(this);
+			if((recycler == null || appBar == null) && !context.IsDesignerContext())
+			{
+				if (recycler == null)
+					throw new ArgumentNullException("flyoutcontent_recycler", "Unable to find layout for flyoutcontent_recycler");
+
+				// PREVIEWER HACK for some reason previewer pulls this out as a FrameLayout and ignores the internal resources
+				if (appBar == null)
+					throw new ArgumentNullException("flyoutcontent_appbar", "Unable to find layout for flyoutcontent_recycler");
+
+			}
+
+
+			try
+			{
+				// PREVIEWER HACK for some reason previewer can't find the resources for the recycler or the appBar
+				if (recycler == null)
+					recycler = (RecyclerView)coordinator.GetChildAt(1);
+				if (appBar == null)
+					appBar = (AppBarLayout)coordinator.GetChildAt(0);
+			}
+			catch
+			{
+				// PReviewer hack.
+				// appcompat and non appcompat initialize this whole thing differently so the above are for appcompat the below are for non
+			}
+
+			// PREVIEWER HACK for some reason previewer can't find the resources for the recycler or the appBar
+			if (recycler == null)
+				recycler = coordinator.FindViewById<RecyclerView>(context.Resources.GetIdentifier("flyoutcontent_recycler", "id", context.PackageName));
+
+			// PREVIEWER HACK for some reason previewer pulls this out as a FrameLayout and ignores the internal resources
+			if (appBar == null)
+				appBar = coordinator.FindViewById<ViewGroup>(context.Resources.GetIdentifier("flyoutcontent_appbar", "id", context.PackageName));
+
+
+			(appBar as AppBarLayout)?.AddOnOffsetChangedListener(this);
 
             int actionBarHeight = (int)context.ToPixels(56);
 
@@ -68,11 +103,14 @@ namespace Xamarin.Forms.Platform.Android
             var metrics = context.Resources.DisplayMetrics;
             var width = Math.Min(metrics.WidthPixels, metrics.HeightPixels);
 
-            TypedValue tv = new TypedValue();
-            if (context.Theme.ResolveAttribute(global::Android.Resource.Attribute.ActionBarSize, tv, true))
-            {
-                actionBarHeight = TypedValue.ComplexToDimensionPixelSize(tv.Data, metrics);
-            }
+			using (TypedValue tv = new TypedValue())
+			{
+				if (context.Theme.ResolveAttribute(global::Android.Resource.Attribute.ActionBarSize, tv, true))
+				{
+					actionBarHeight = TypedValue.ComplexToDimensionPixelSize(tv.Data, metrics);
+				}
+			}
+
             width -= actionBarHeight;
 
             coordinator.LayoutParameters = new LP(width, LP.MatchParent);

Xamarin.Forms.Platform.Android/Renderers/ShellRenderer.cs

@@ -36,7 +36,10 @@ namespace Xamarin.Forms.Platform.Android
 		VisualElementTracker IVisualElementRenderer.Tracker => null;
 
 		AView IVisualElementRenderer.View => _flyoutRenderer.AndroidView;
-		ViewGroup IVisualElementRenderer.ViewGroup => _flyoutRenderer.AndroidView as ViewGroup;
+
+		// Used by Previewer
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public ViewGroup ViewGroup => _flyoutRenderer.AndroidView as ViewGroup;
 
 		SizeRequest IVisualElementRenderer.GetDesiredSize(int widthConstraint, int heightConstraint)
 		{
@@ -59,7 +62,9 @@ namespace Xamarin.Forms.Platform.Android
 		{
 		}
 
-		void IVisualElementRenderer.UpdateLayout()
+		// Used by Previewer
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public void UpdateLayout()
 		{
 			var width = (int)AndroidContext.ToPixels(Element.Width);
 			var height = (int)AndroidContext.ToPixels(Element.Height);
@@ -151,7 +156,7 @@ namespace Xamarin.Forms.Platform.Android
 
 		protected Context AndroidContext { get; }
 		protected Shell Element { get; private set; }
-		private FragmentManager FragmentManager => ((FormsAppCompatActivity)AndroidContext).SupportFragmentManager;
+		FragmentManager FragmentManager => AndroidContext.GetFragmentManager();
 
 		protected virtual IShellObservableFragment CreateFragmentForPage(Page page)
 		{
@@ -202,9 +207,7 @@ namespace Xamarin.Forms.Platform.Android
 		protected virtual void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
 		{
 			if (e.PropertyName == Shell.CurrentItemProperty.PropertyName)
-			{
 				SwitchFragment(FragmentManager, _frameLayout, Element.CurrentItem);
-			}
 
 			_elementPropertyChanged?.Invoke(sender, e);
 		}
@@ -223,13 +226,18 @@ namespace Xamarin.Forms.Platform.Android
 
 			((IShellController)shell).AddAppearanceObserver(this, shell);
 
-			SwitchFragment(FragmentManager, _frameLayout, shell.CurrentItem, false);
+			// Previewer Hack
+			if(AndroidContext.GetActivity() != null)
+				SwitchFragment(FragmentManager, _frameLayout, shell.CurrentItem, false);
 		}
 
 		IShellItemRenderer _currentRenderer;
 
 		protected virtual void SwitchFragment(FragmentManager manager, AView targetView, ShellItem newItem, bool animate = true)
 		{
+			if (AndroidContext.IsDesignerContext())
+				return; 
+
 			var previousRenderer = _currentRenderer;
 			_currentRenderer = CreateShellItemRenderer(newItem);
 			_currentRenderer.ShellItem = newItem;
@@ -266,10 +274,10 @@ namespace Xamarin.Forms.Platform.Android
 
 		void UpdateStatusBarColor(ShellAppearance appearance)
 		{
-			var activity = ((FormsAppCompatActivity)AndroidContext);
-			var window = activity.Window;
-			var decorView = window.DecorView;
-			var resources = activity.Resources;
+			var activity = AndroidContext.GetActivity();
+			var window = activity?.Window;
+			var decorView = window?.DecorView;
+			var resources = AndroidContext.Resources;
 
 			int statusBarHeight = 0;
 			int resourceId = resources.GetIdentifier("status_bar_height", "dimen", "android");
@@ -285,19 +293,23 @@ namespace Xamarin.Forms.Platform.Android
 				navigationBarHeight = resources.GetDimensionPixelSize(resourceId);
 			}
 
-			// we are using the split drawable here to avoid GPU overdraw.
-			// All it really is is a drawable that only draws under the statusbar/bottom bar to make sure
-			// we dont draw over areas we dont need to. This has very limited benefits considering its
-			// only saving us a flat color fill BUT it helps people not freak out about overdraw.
-			if (appearance != null)
+			// TODO Previewer Hack
+			if (decorView != null)
 			{
-				var color = appearance.BackgroundColor.ToAndroid(Color.FromHex("#03A9F4"));
-				decorView.SetBackground(new SplitDrawable(color, statusBarHeight, navigationBarHeight));
-			}
-			else
-			{
-				var color = Color.FromHex("#03A9F4").ToAndroid();
-				decorView.SetBackground(new SplitDrawable(color, statusBarHeight, navigationBarHeight));
+				// we are using the split drawable here to avoid GPU overdraw.
+				// All it really is is a drawable that only draws under the statusbar/bottom bar to make sure
+				// we dont draw over areas we dont need to. This has very limited benefits considering its
+				// only saving us a flat color fill BUT it helps people not freak out about overdraw.
+				if (appearance != null)
+				{
+					var color = appearance.BackgroundColor.ToAndroid(Color.FromHex("#03A9F4"));
+					decorView.SetBackground(new SplitDrawable(color, statusBarHeight, navigationBarHeight));
+				}
+				else
+				{
+					var color = Color.FromHex("#03A9F4").ToAndroid();
+					decorView.SetBackground(new SplitDrawable(color, statusBarHeight, navigationBarHeight));
+				}
 			}
 		}
 

Xamarin.Forms.Platform.Android/Renderers/ShellToolbarTracker.cs

@@ -236,23 +236,21 @@ namespace Xamarin.Forms.Platform.Android
 			var backButtonHandler = Shell.GetBackButtonBehavior(page);
 			toolbar.SetNavigationOnClickListener(this);
 
-			var activity = (FormsAppCompatActivity)context;
-
 			if (backButtonHandler != null)
 			{
-				await UpdateDrawerArrowFromBackButtonBehavior(context, toolbar, drawerLayout, backButtonHandler, activity);
+				await UpdateDrawerArrowFromBackButtonBehavior(context, toolbar, drawerLayout, backButtonHandler);
 			}
 			else
 			{
-				await UpdateDrawerArrow(context, toolbar, drawerLayout, activity);
+				await UpdateDrawerArrow(context, toolbar, drawerLayout);
 			}
 		}
 
-		protected virtual async Task UpdateDrawerArrow(Context context, Toolbar toolbar, DrawerLayout drawerLayout, FormsAppCompatActivity activity)
+		protected virtual async Task UpdateDrawerArrow(Context context, Toolbar toolbar, DrawerLayout drawerLayout)
 		{
-			if (_drawerToggle == null)
+			if (_drawerToggle == null && !context.IsDesignerContext())
 			{
-				_drawerToggle = new ActionBarDrawerToggle((Activity)context, drawerLayout, toolbar,
+				_drawerToggle = new ActionBarDrawerToggle(context.GetActivity(), drawerLayout, toolbar,
 					R.String.Ok, R.String.Ok)
 				{
 					ToolbarNavigationClickListener = this,
@@ -267,7 +265,7 @@ namespace Xamarin.Forms.Platform.Android
 			if (CanNavigateBack)
 			{
 				_drawerToggle.DrawerIndicatorEnabled = false;
-				using (var icon = new DrawerArrowDrawable(activity.SupportActionBar.ThemedContext))
+				using (var icon = new DrawerArrowDrawable(context.GetThemedContext()))
 				{
 					icon.SetColorFilter(TintColor.ToAndroid(Color.White), PorterDuff.Mode.SrcAtop);
 					icon.Progress = 1;
@@ -288,7 +286,7 @@ namespace Xamarin.Forms.Platform.Android
 			_drawerToggle.SyncState();
 		}
 
-		protected virtual async Task UpdateDrawerArrowFromBackButtonBehavior(Context context, Toolbar toolbar, DrawerLayout drawerLayout, BackButtonBehavior backButtonHandler, FormsAppCompatActivity activity)
+		protected virtual async Task UpdateDrawerArrowFromBackButtonBehavior(Context context, Toolbar toolbar, DrawerLayout drawerLayout, BackButtonBehavior backButtonHandler)
 		{
 			var behavior = backButtonHandler;
 			var command = behavior.Command;
@@ -307,7 +305,7 @@ namespace Xamarin.Forms.Platform.Android
 
 			if (CanNavigateBack && icon == null)
 			{
-				icon = new DrawerArrowDrawable(activity.SupportActionBar.ThemedContext);
+				icon = new DrawerArrowDrawable(context.GetThemedContext());
 				(icon as DrawerArrowDrawable).Progress = 1;
 			}
 

Xamarin.Forms.Platform.Android/Resources/Layout/FlyoutContent.axml

@@ -9,13 +9,13 @@
 		>
 
 	<android.support.design.widget.AppBarLayout
-			android:id="@+id/flyoutcontent.appbar"
+			android:id="@+id/flyoutcontent_appbar"
 			android:layout_width="match_parent"
 			android:layout_height="wrap_content"
 			android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" />
 
 	<android.support.v7.widget.RecyclerView
-		android:id="@+id/flyoutcontent.recycler"
+		android:id="@+id/flyoutcontent_recycler"
 		android:layout_width="match_parent"
 		android:layout_height="match_parent"
 		app:layout_behavior="@string/appbar_scrolling_view_behavior" />

Xamarin.Forms.Sandbox/ShellPage.xaml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Shell xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Xamarin.Forms.Sandbox.ShellPage">
+
+    <ShellContent Title="test">
+        <ContentPage></ContentPage>
+    </ShellContent>
+</Shell>

Xamarin.Forms.Sandbox/ShellPage.xaml.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using Xamarin.Forms;
+using Xamarin.Forms.Xaml;
+
+namespace Xamarin.Forms.Sandbox
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	public partial class ShellPage : Shell
+	{
+		public ShellPage()
+		{
+			InitializeComponent();
+		}
+	}
+}

Xamarin.Forms.Sandbox/Xamarin.Forms.Sandbox.csproj

@@ -13,6 +13,12 @@
     <DebugType>pdbonly</DebugType>
     <DebugSymbols>true</DebugSymbols>
   </PropertyGroup>
+
+  <ItemGroup>
+    <None Include="ShellPage.xaml">
+      <Generator>MSBuild:Compile</Generator>
+    </None>
+  </ItemGroup>
   
   <ItemGroup>
     <!-- A reference to the entire .NET Framework is automatically included -->