Fix NullReferenceException when displaying Toast or SnackBar (#963)

maxkoshevoi · web-flow · commit 5b6b4f089715 · 2021-04-19T14:57:49.000-03:00
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Extensions/PageExtension.shared.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Extensions/PageExtension.shared.cs
@@ -10,7 +10,7 @@ namespace Xamarin.CommunityToolkit.Extensions
 {
 	public static class PageExtension
 	{
-		public static Task DisplayToastAsync(this Page page, string message, int durationMilliseconds = 3000)
+		public static async Task DisplayToastAsync(this Page page, string message, int durationMilliseconds = 3000)
 		{
 			_ = page ?? throw new ArgumentNullException(nameof(page));
 
@@ -26,11 +26,11 @@ public static Task DisplayToastAsync(this Page page, string message, int duratio
 #endif
 			};
 			var snackBar = new SnackBar();
-			snackBar.Show(page, args);
-			return args.Result.Task;
+			await snackBar.Show(page, args);
+			await args.Result.Task;
 		}
 
-		public static Task DisplayToastAsync(this Page page, ToastOptions toastOptions)
+		public static async Task DisplayToastAsync(this Page page, ToastOptions toastOptions)
 		{
 			_ = page ?? throw new ArgumentNullException(nameof(page));
 
@@ -43,11 +43,11 @@ public static Task DisplayToastAsync(this Page page, ToastOptions toastOptions)
 				BackgroundColor = arguments.BackgroundColor,
 				IsRtl = arguments.IsRtl
 			};
-			snackBar.Show(page, options);
-			return options.Result.Task;
+			await snackBar.Show(page, options);
+			await options.Result.Task;
 		}
 
-		public static Task<bool> DisplaySnackBarAsync(this Page page, string message, string actionButtonText, Func<Task> action, int durationMilliseconds = 3000)
+		public static async Task<bool> DisplaySnackBarAsync(this Page page, string message, string actionButtonText, Func<Task> action, int durationMilliseconds = 3000)
 		{
 			_ = page ?? throw new ArgumentNullException(nameof(page));
 
@@ -71,18 +71,22 @@ public static Task<bool> DisplaySnackBarAsync(this Page page, string message, st
 #endif
 			};
 			var snackBar = new SnackBar();
-			snackBar.Show(page, options);
-			return options.Result.Task;
+			await snackBar.Show(page, options);
+			var isButtonClicked = await options.Result.Task;
+
+			return isButtonClicked;
 		}
 
-		public static Task<bool> DisplaySnackBarAsync(this Page page, SnackBarOptions snackBarOptions)
+		public static async Task<bool> DisplaySnackBarAsync(this Page page, SnackBarOptions snackBarOptions)
 		{
 			_ = page ?? throw new ArgumentNullException(nameof(page));
 
 			var snackBar = new SnackBar();
-			var arguments = snackBarOptions ?? new SnackBarOptions();
-			snackBar.Show(page, arguments);
-			return arguments.Result.Task;
+			var options = snackBarOptions ?? new SnackBarOptions();
+			await snackBar.Show(page, options);
+			var isButtonClicked = await options.Result.Task;
+
+			return isButtonClicked;
 		}
 	}
 }
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.android.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.android.cs
@@ -1,10 +1,11 @@
-﻿using Xamarin.Forms;
+﻿using System;
+using System.Threading.Tasks;
+using Xamarin.Forms;
 using Android.Graphics;
 using Android.Widget;
 using Xamarin.Forms.Platform.Android;
 using Xamarin.CommunityToolkit.UI.Views.Options;
 using Android.Util;
-using System;
 #if MONOANDROID10_0
 using AndroidSnackBar = Google.Android.Material.Snackbar.Snackbar;
 #else
@@ -15,10 +16,10 @@ namespace Xamarin.CommunityToolkit.UI.Views
 {
 	class SnackBar
 	{
-		internal void Show(Page sender, SnackBarOptions arguments)
+		internal async ValueTask Show(Page sender, SnackBarOptions arguments)
 		{
-			var view = Platform.GetRenderer(sender).View;
-			var snackBar = AndroidSnackBar.Make(view, arguments.MessageOptions.Message, (int)arguments.Duration.TotalMilliseconds);
+			var renderer = await GetRendererWithRetries(sender) ?? throw new ArgumentException("Provided page cannot be parent to SnackBar", nameof(sender));
+			var snackBar = AndroidSnackBar.Make(renderer.View, arguments.MessageOptions.Message, (int)arguments.Duration.TotalMilliseconds);
 			var snackBarView = snackBar.View;
 			if (arguments.BackgroundColor != Forms.Color.Default)
 			{
@@ -100,6 +101,20 @@ internal void Show(Page sender, SnackBarOptions arguments)
 			snackBar.Show();
 		}
 
+		/// <summary>
+		/// Tries to get renderer multiple times since it can be null while switching tabs in Shell.
+		/// See this bug for more info: https://github.com/xamarin/Xamarin.Forms/issues/13950
+		/// </summary>
+		static async Task<IVisualElementRenderer?> GetRendererWithRetries(Page page, int retryCount = 5)
+		{
+			var renderer = Platform.GetRenderer(page);
+			if (renderer != null || retryCount <= 0)
+				return renderer;
+
+			await Task.Delay(50);
+			return await GetRendererWithRetries(page, retryCount - 1);
+		}
+
 		class SnackBarCallback : AndroidSnackBar.BaseCallback
 		{
 			readonly SnackBarOptions arguments;
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.gtk.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.gtk.cs
@@ -1,4 +1,5 @@
 ﻿using System.Linq;
+using System.Threading.Tasks;
 using System.Timers;
 using Gtk;
 using Pango;
@@ -13,7 +14,7 @@ class SnackBar
 	{
 		Timer? snackBarTimer;
 
-		public void Show(Page page, SnackBarOptions arguments)
+		public ValueTask Show(Page page, SnackBarOptions arguments)
 		{
 			var mainWindow = (Platform.GetRenderer(page).Container.Child as Forms.Platform.GTK.Controls.Page)?.Children[0] as VBox;
 			var snackBarLayout = GetSnackBarLayout(mainWindow, arguments);
@@ -29,6 +30,7 @@ public void Show(Page page, SnackBarOptions arguments)
 			};
 
 			snackBarTimer.Start();
+			return default;
 		}
 
 		HBox GetSnackBarLayout(Container? container, SnackBarOptions arguments)
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.ios.macos.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.ios.macos.cs
@@ -17,7 +17,7 @@ namespace Xamarin.CommunityToolkit.UI.Views
 {
 	class SnackBar
 	{
-		internal void Show(Page sender, SnackBarOptions arguments)
+		internal ValueTask Show(Page sender, SnackBarOptions arguments)
 		{
 			var snackBar = NativeSnackBar.MakeSnackBar(arguments.MessageOptions.Message)
 							.SetDuration(arguments.Duration.TotalMilliseconds)
@@ -124,6 +124,8 @@ internal void Show(Page sender, SnackBarOptions arguments)
 			}
 
 			snackBar.Show();
+
+			return default;
 		}
 	}
 }
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.netstandard.tvos.watchos.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.netstandard.tvos.watchos.cs
@@ -1,11 +1,12 @@
 ﻿using System;
+using System.Threading.Tasks;
 using Xamarin.CommunityToolkit.UI.Views.Options;
 using Xamarin.Forms;
 
 namespace Xamarin.CommunityToolkit.UI.Views
 {
 	class SnackBar
 	{
-		internal void Show(Page sender, SnackBarOptions arguments) => throw new PlatformNotSupportedException();
+		internal ValueTask Show(Page sender, SnackBarOptions arguments) => throw new PlatformNotSupportedException();
 	}
 }
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.tizen.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.tizen.cs
@@ -1,13 +1,14 @@
 ﻿using System;
 using System.Linq;
+using System.Threading.Tasks;
 using Xamarin.CommunityToolkit.UI.Views.Options;
 using EButton = ElmSharp.Button;
 
 namespace Xamarin.CommunityToolkit.UI.Views
 {
 	class SnackBar
 	{
-		internal void Show(Forms.Page sender, SnackBarOptions arguments)
+		internal ValueTask Show(Forms.Page sender, SnackBarOptions arguments)
 		{
 			var snackBarDialog =
 				Forms.Platform.Tizen.Native.Dialog.CreateDialog(Forms.Forms.NativeParent,
@@ -36,11 +37,11 @@ internal void Show(Forms.Page sender, SnackBarOptions arguments)
 			}
 
 			snackBarDialog.TimedOut += (s, evt) => DismissSnackBar();
-
 			snackBarDialog.BackButtonPressed += (s, evt) => DismissSnackBar();
-
 			snackBarDialog.Show();
 
+			return default;
+
 			void DismissSnackBar()
 			{
 				snackBarDialog.Dismiss();
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.uwp.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.uwp.cs
@@ -1,4 +1,5 @@
 ﻿using System;
+using System.Threading.Tasks;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Media;
@@ -34,7 +35,7 @@ class SnackBar
 			return null;
 		}
 
-		internal void Show(Forms.Page page, SnackBarOptions arguments)
+		internal ValueTask Show(Forms.Page page, SnackBarOptions arguments)
 		{
 			var snackBarLayout = new SnackBarLayout(arguments);
 			var pageControl = Platform.GetRenderer(page).ContainerElement.Parent;
@@ -59,6 +60,7 @@ internal void Show(Forms.Page page, SnackBarOptions arguments)
 			grid.RowDefinitions.Add(snackBarRow);
 			grid.Children.Add(snackBarLayout);
 			Grid.SetRow(snackBarLayout, grid.RowDefinitions.Count - 1);
+			return default;
 		}
 	}
 }
diff --git a/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.wpf.cs b/src/CommunityToolkit/Xamarin.CommunityToolkit/Views/Snackbar/SnackBar.wpf.cs
@@ -1,4 +1,5 @@
-﻿using System.Windows.Forms;
+﻿using System.Threading.Tasks;
+using System.Windows.Forms;
 using Xamarin.CommunityToolkit.UI.Views.Helpers;
 using Xamarin.CommunityToolkit.UI.Views.Options;
 using Xamarin.Forms;
@@ -11,7 +12,7 @@ class SnackBar
 	{
 		Timer? snackBarTimer;
 
-		internal void Show(Page page, SnackBarOptions arguments)
+		internal ValueTask Show(Page page, SnackBarOptions arguments)
 		{
 			var formsAppBar = System.Windows.Application.Current.MainWindow.FindChild<FormsAppBar>("PART_BottomAppBar");
 			var currentContent = formsAppBar.Content;
@@ -31,6 +32,7 @@ internal void Show(Page page, SnackBarOptions arguments)
 			};
 			snackBarTimer.Start();
 			formsAppBar.Content = snackBar;
+			return default;
 		}
 	}
 }

Original file line number	Diff line number	Diff line change
`@@ -10,7 +10,7 @@ namespace Xamarin.CommunityToolkit.Extensions`
`10`	`10`	`{`
`11`	`11`	`public static class PageExtension`
`12`	`12`	`{`
`13`		`- public static Task DisplayToastAsync(this Page page, string message, int durationMilliseconds = 3000)`
	`13`	`+ public static async Task DisplayToastAsync(this Page page, string message, int durationMilliseconds = 3000)`
`14`	`14`	`{`
`15`	`15`	`_ = page ?? throw new ArgumentNullException(nameof(page));`
`16`	`16`
`@@ -26,11 +26,11 @@ public static Task DisplayToastAsync(this Page page, string message, int duratio`
`26`	`26`	`#endif`
`27`	`27`	`};`
`28`	`28`	`var snackBar = new SnackBar();`
`29`		`- snackBar.Show(page, args);`
`30`		`- return args.Result.Task;`
	`29`	`+ await snackBar.Show(page, args);`
	`30`	`+ await args.Result.Task;`
`31`	`31`	`}`
`32`	`32`
`33`		`- public static Task DisplayToastAsync(this Page page, ToastOptions toastOptions)`
	`33`	`+ public static async Task DisplayToastAsync(this Page page, ToastOptions toastOptions)`
`34`	`34`	`{`
`35`	`35`	`_ = page ?? throw new ArgumentNullException(nameof(page));`
`36`	`36`
`@@ -43,11 +43,11 @@ public static Task DisplayToastAsync(this Page page, ToastOptions toastOptions)`
`43`	`43`	`BackgroundColor = arguments.BackgroundColor,`
`44`	`44`	`IsRtl = arguments.IsRtl`
`45`	`45`	`};`
`46`		`- snackBar.Show(page, options);`
`47`		`- return options.Result.Task;`
	`46`	`+ await snackBar.Show(page, options);`
	`47`	`+ await options.Result.Task;`
`48`	`48`	`}`
`49`	`49`
`50`		`- public static Task<bool> DisplaySnackBarAsync(this Page page, string message, string actionButtonText, Func<Task> action, int durationMilliseconds = 3000)`
	`50`	`+ public static async Task<bool> DisplaySnackBarAsync(this Page page, string message, string actionButtonText, Func<Task> action, int durationMilliseconds = 3000)`
`51`	`51`	`{`
`52`	`52`	`_ = page ?? throw new ArgumentNullException(nameof(page));`
`53`	`53`
`@@ -71,18 +71,22 @@ public static Task<bool> DisplaySnackBarAsync(this Page page, string message, st`
`71`	`71`	`#endif`
`72`	`72`	`};`
`73`	`73`	`var snackBar = new SnackBar();`
`74`		`- snackBar.Show(page, options);`
`75`		`- return options.Result.Task;`
	`74`	`+ await snackBar.Show(page, options);`
	`75`	`+ var isButtonClicked = await options.Result.Task;`
	`76`	`+`
	`77`	`+ return isButtonClicked;`
`76`	`78`	`}`
`77`	`79`
`78`		`- public static Task<bool> DisplaySnackBarAsync(this Page page, SnackBarOptions snackBarOptions)`
	`80`	`+ public static async Task<bool> DisplaySnackBarAsync(this Page page, SnackBarOptions snackBarOptions)`
`79`	`81`	`{`
`80`	`82`	`_ = page ?? throw new ArgumentNullException(nameof(page));`
`81`	`83`
`82`	`84`	`var snackBar = new SnackBar();`
`83`		`- var arguments = snackBarOptions ?? new SnackBarOptions();`
`84`		`- snackBar.Show(page, arguments);`
`85`		`- return arguments.Result.Task;`
	`85`	`+ var options = snackBarOptions ?? new SnackBarOptions();`
	`86`	`+ await snackBar.Show(page, options);`
	`87`	`+ var isButtonClicked = await options.Result.Task;`
	`88`	`+`
	`89`	`+ return isButtonClicked;`
`86`	`90`	`}`
`87`	`91`	`}`
`88`	`92`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,5 @@`
`1`	`1`	`using System.Linq;`
	`2`	`+using System.Threading.Tasks;`
`2`	`3`	`using System.Timers;`
`3`	`4`	`using Gtk;`
`4`	`5`	`using Pango;`
`@@ -13,7 +14,7 @@ class SnackBar`
`13`	`14`	`{`
`14`	`15`	`Timer? snackBarTimer;`
`15`	`16`
`16`		`- public void Show(Page page, SnackBarOptions arguments)`
	`17`	`+ public ValueTask Show(Page page, SnackBarOptions arguments)`
`17`	`18`	`{`
`18`	`19`	`var mainWindow = (Platform.GetRenderer(page).Container.Child as Forms.Platform.GTK.Controls.Page)?.Children[0] as VBox;`
`19`	`20`	`var snackBarLayout = GetSnackBarLayout(mainWindow, arguments);`
`@@ -29,6 +30,7 @@ public void Show(Page page, SnackBarOptions arguments)`
`29`	`30`	`};`
`30`	`31`
`31`	`32`	`snackBarTimer.Start();`
	`33`	`+ return default;`
`32`	`34`	`}`
`33`	`35`
`34`	`36`	`HBox GetSnackBarLayout(Container? container, SnackBarOptions arguments)`
Original file line number	Diff line number	Diff line change
`@@ -17,7 +17,7 @@ namespace Xamarin.CommunityToolkit.UI.Views`
`17`	`17`	`{`
`18`	`18`	`class SnackBar`
`19`	`19`	`{`
`20`		`- internal void Show(Page sender, SnackBarOptions arguments)`
	`20`	`+ internal ValueTask Show(Page sender, SnackBarOptions arguments)`
`21`	`21`	`{`
`22`	`22`	`var snackBar = NativeSnackBar.MakeSnackBar(arguments.MessageOptions.Message)`
`23`	`23`	`.SetDuration(arguments.Duration.TotalMilliseconds)`
`@@ -124,6 +124,8 @@ internal void Show(Page sender, SnackBarOptions arguments)`
`124`	`124`	`}`
`125`	`125`
`126`	`126`	`snackBar.Show();`
	`127`	`+`
	`128`	`+ return default;`
`127`	`129`	`}`
`128`	`130`	`}`
`129`	`131`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1,11 +1,12 @@`
`1`	`1`	`using System;`
	`2`	`+using System.Threading.Tasks;`
`2`	`3`	`using Xamarin.CommunityToolkit.UI.Views.Options;`
`3`	`4`	`using Xamarin.Forms;`
`4`	`5`
`5`	`6`	`namespace Xamarin.CommunityToolkit.UI.Views`
`6`	`7`	`{`
`7`	`8`	`class SnackBar`
`8`	`9`	`{`
`9`		`- internal void Show(Page sender, SnackBarOptions arguments) => throw new PlatformNotSupportedException();`
	`10`	`+ internal ValueTask Show(Page sender, SnackBarOptions arguments) => throw new PlatformNotSupportedException();`
`10`	`11`	`}`
`11`	`12`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1,13 +1,14 @@`
`1`	`1`	`using System;`
`2`	`2`	`using System.Linq;`
	`3`	`+using System.Threading.Tasks;`
`3`	`4`	`using Xamarin.CommunityToolkit.UI.Views.Options;`
`4`	`5`	`using EButton = ElmSharp.Button;`
`5`	`6`
`6`	`7`	`namespace Xamarin.CommunityToolkit.UI.Views`
`7`	`8`	`{`
`8`	`9`	`class SnackBar`
`9`	`10`	`{`
`10`		`- internal void Show(Forms.Page sender, SnackBarOptions arguments)`
	`11`	`+ internal ValueTask Show(Forms.Page sender, SnackBarOptions arguments)`
`11`	`12`	`{`
`12`	`13`	`var snackBarDialog =`
`13`	`14`	`Forms.Platform.Tizen.Native.Dialog.CreateDialog(Forms.Forms.NativeParent,`
`@@ -36,11 +37,11 @@ internal void Show(Forms.Page sender, SnackBarOptions arguments)`
`36`	`37`	`}`
`37`	`38`
`38`	`39`	`snackBarDialog.TimedOut += (s, evt) => DismissSnackBar();`
`39`		`-`
`40`	`40`	`snackBarDialog.BackButtonPressed += (s, evt) => DismissSnackBar();`
`41`		`-`
`42`	`41`	`snackBarDialog.Show();`
`43`	`42`
	`43`	`+ return default;`
	`44`	`+`
`44`	`45`	`void DismissSnackBar()`
`45`	`46`	`{`
`46`	`47`	`snackBarDialog.Dismiss();`
Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,5 @@`
`1`		`-using System.Windows.Forms;`
	`1`	`+using System.Threading.Tasks;`
	`2`	`+using System.Windows.Forms;`
`2`	`3`	`using Xamarin.CommunityToolkit.UI.Views.Helpers;`
`3`	`4`	`using Xamarin.CommunityToolkit.UI.Views.Options;`
`4`	`5`	`using Xamarin.Forms;`
`@@ -11,7 +12,7 @@ class SnackBar`
`11`	`12`	`{`
`12`	`13`	`Timer? snackBarTimer;`
`13`	`14`
`14`		`- internal void Show(Page page, SnackBarOptions arguments)`
	`15`	`+ internal ValueTask Show(Page page, SnackBarOptions arguments)`
`15`	`16`	`{`
`16`	`17`	`var formsAppBar = System.Windows.Application.Current.MainWindow.FindChild<FormsAppBar>("PART_BottomAppBar");`
`17`	`18`	`var currentContent = formsAppBar.Content;`
`@@ -31,6 +32,7 @@ internal void Show(Page page, SnackBarOptions arguments)`
`31`	`32`	`};`
`32`	`33`	`snackBarTimer.Start();`
`33`	`34`	`formsAppBar.Content = snackBar;`
	`35`	`+ return default;`
`34`	`36`	`}`
`35`	`37`	`}`
`36`	`38`	`}`