Merge pull request #9856 from AvaloniaUI/back_request

Add BackRequested event for TopLevel

src/Android/Avalonia.Android/AvaloniaMainActivity.cs

@@ -1,18 +1,14 @@
 using System;
 using Android.App;
 using Android.Content;
-using Android.Content.Res;
 using Android.OS;
 using Android.Runtime;
 using Android.Views;
 using AndroidX.AppCompat.App;
-using AndroidX.Lifecycle;
-
-using AndroidRect = Android.Graphics.Rect;
 
 namespace Avalonia.Android
 {
-    public abstract class AvaloniaMainActivity : AppCompatActivity, IActivityResultHandler
+    public abstract class AvaloniaMainActivity : AppCompatActivity, IActivityResultHandler, IActivityNavigationService
     {
         internal static object ViewContent;
 
@@ -56,9 +52,18 @@ namespace Avalonia.Android
             }
         }
 
-        public override void OnConfigurationChanged(Configuration newConfig)
+        public event EventHandler<AndroidBackRequestedEventArgs> BackRequested;
+
+        public override void OnBackPressed()
         {
-            base.OnConfigurationChanged(newConfig);
+            var eventArgs = new AndroidBackRequestedEventArgs();
+
+            BackRequested?.Invoke(this, eventArgs);
+
+            if (!eventArgs.Handled)
+            {
+                base.OnBackPressed();
+            }
         }
 
         protected override void OnDestroy()

src/Android/Avalonia.Android/IAndroidNavigationService.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace Avalonia.Android
+{
+    public interface IActivityNavigationService
+    {
+        event EventHandler<AndroidBackRequestedEventArgs> BackRequested;
+    }
+
+    public class AndroidBackRequestedEventArgs : EventArgs
+    {
+        public bool Handled { get; set; }
+    }
+}

src/Android/Avalonia.Android/Platform/AndroidSystemNavigationManager.cs

@@ -0,0 +1,28 @@
+using System;
+using Avalonia.Interactivity;
+using Avalonia.Platform;
+
+namespace Avalonia.Android.Platform
+{
+    internal class AndroidSystemNavigationManager : ISystemNavigationManager
+    {
+        public event EventHandler<RoutedEventArgs> BackRequested;
+
+        public AndroidSystemNavigationManager(IActivityNavigationService? navigationService)
+        {
+            if(navigationService != null)
+            {
+                navigationService.BackRequested += OnBackRequested;
+            }
+        }
+
+        private void OnBackRequested(object sender, AndroidBackRequestedEventArgs e)
+        {
+            var routedEventArgs = new RoutedEventArgs();
+
+            BackRequested?.Invoke(this, routedEventArgs);
+
+            e.Handled = routedEventArgs.Handled;
+        }
+    }
+}

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -32,7 +32,8 @@ using Android.Graphics.Drawables;
 namespace Avalonia.Android.Platform.SkiaPlatform
 {
     class TopLevelImpl : IAndroidView, ITopLevelImpl, EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo,
-        ITopLevelImplWithTextInputMethod, ITopLevelImplWithNativeControlHost, ITopLevelImplWithStorageProvider
+        ITopLevelImplWithTextInputMethod, ITopLevelImplWithNativeControlHost, ITopLevelImplWithStorageProvider,
+        ITopLevelWithSystemNavigationManager
     {
         private readonly IGlPlatformSurface _gl;
         private readonly IFramebufferPlatformSurface _framebuffer;
@@ -58,6 +59,8 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
             NativeControlHost = new AndroidNativeControlHostImpl(avaloniaView);
             StorageProvider = new AndroidStorageProvider((Activity)avaloniaView.Context);
+
+            SystemNavigationManager = new AndroidSystemNavigationManager(avaloniaView.Context as IActivityNavigationService);
         }
 
         public virtual Point GetAvaloniaPointFromEvent(MotionEvent e, int pointerIndex) =>
@@ -306,6 +309,8 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         
         public IStorageProvider StorageProvider { get; }
 
+        public ISystemNavigationManager SystemNavigationManager { get; }
+
         public void SetTransparencyLevelHint(WindowTransparencyLevel transparencyLevel)
         {
             if (TransparencyLevel != transparencyLevel)

src/Avalonia.Base/Input/Platform/PlatformHotkeyConfiguration.cs

@@ -81,6 +81,10 @@ namespace Avalonia.Input.Platform
             {
                 new KeyGesture(Key.Apps)
             };
+            Back = new List<KeyGesture>
+            {
+                new KeyGesture(Key.Left, KeyModifiers.Alt)
+            };
         }
 
         public KeyModifiers CommandModifiers { get; set; }
@@ -101,5 +105,6 @@ namespace Avalonia.Input.Platform
         public List<KeyGesture> MoveCursorToTheStartOfDocumentWithSelection { get; set; }
         public List<KeyGesture> MoveCursorToTheEndOfDocumentWithSelection { get; set; }
         public List<KeyGesture> OpenContextMenu { get; set; }
+        public List<KeyGesture> Back { get; set; }
     }
 }

src/Avalonia.Base/Platform/SystemNavigationManager.cs

@@ -0,0 +1,18 @@
+using System;
+using Avalonia.Interactivity;
+using Avalonia.Metadata;
+
+namespace Avalonia.Platform
+{
+    [Unstable]
+    public interface ITopLevelWithSystemNavigationManager
+    {
+        ISystemNavigationManager SystemNavigationManager { get; }
+    }
+
+    [Unstable]
+    public interface ISystemNavigationManager
+    {
+        public event EventHandler<RoutedEventArgs>? BackRequested;
+    }
+}

src/Avalonia.Controls/TopLevel.cs

@@ -7,6 +7,7 @@ using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Input.TextInput;
+using Avalonia.Interactivity;
 using Avalonia.Layout;
 using Avalonia.Logging;
 using Avalonia.LogicalTree;
@@ -17,6 +18,8 @@ using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.Utilities;
 using Avalonia.VisualTree;
+using Avalonia.Input.Platform;
+using System.Linq;
 
 namespace Avalonia.Controls
 {
@@ -76,6 +79,12 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<IBrush> TransparencyBackgroundFallbackProperty =
             AvaloniaProperty.Register<TopLevel, IBrush>(nameof(TransparencyBackgroundFallback), Brushes.White);
 
+        /// <summary>
+        /// Defines the <see cref="BackRequested"/> event.
+        /// </summary>
+        public static readonly RoutedEvent<RoutedEventArgs> BackRequestedEvent = 
+            RoutedEvent.Register<TopLevel, RoutedEventArgs>(nameof(BackRequested), RoutingStrategies.Bubble);
+
         private static readonly WeakEvent<IResourceHost, ResourcesChangedEventArgs>
             ResourcesChangedWeakEvent = WeakEvent.Register<IResourceHost, ResourcesChangedEventArgs>(
                 (s, h) => s.ResourcesChanged += h,
@@ -89,6 +98,7 @@ namespace Avalonia.Controls
         private readonly IGlobalStyles? _globalStyles;
         private readonly PointerOverPreProcessor? _pointerOverPreProcessor;
         private readonly IDisposable? _pointerOverPreProcessorSubscription;
+        private readonly IDisposable? _backGestureSubscription;
         private Size _clientSize;
         private Size? _frameSize;
         private WindowTransparencyLevel _actualTransparencyLevel;
@@ -205,6 +215,48 @@ namespace Avalonia.Controls
 
             _pointerOverPreProcessor = new PointerOverPreProcessor(this);
             _pointerOverPreProcessorSubscription = _inputManager?.PreProcess.Subscribe(_pointerOverPreProcessor);
+
+            if(impl is ITopLevelWithSystemNavigationManager topLevelWithSystemNavigation)
+            {
+                topLevelWithSystemNavigation.SystemNavigationManager.BackRequested += (s, e) =>
+                {
+                    e.RoutedEvent = BackRequestedEvent;
+                    RaiseEvent(e);
+                };
+            }
+
+            _backGestureSubscription = _inputManager?.PreProcess.Subscribe(e =>
+            {
+                bool backRequested = false;
+
+                if (e is RawKeyEventArgs rawKeyEventArgs && rawKeyEventArgs.Type == RawKeyEventType.KeyDown)
+                {
+                    var keymap = AvaloniaLocator.Current.GetService<PlatformHotkeyConfiguration>()?.Back;
+
+                    if (keymap != null)
+                    {
+                        var keyEvent = new KeyEventArgs()
+                        {
+                            KeyModifiers = (KeyModifiers)rawKeyEventArgs.Modifiers,
+                            Key = rawKeyEventArgs.Key
+                        };
+
+                        backRequested = keymap.Any( key => key.Matches(keyEvent));
+                    }
+                }
+                else if(e is RawPointerEventArgs pointerEventArgs)
+                {
+                    backRequested = pointerEventArgs.Type == RawPointerEventType.XButton1Down;
+                }
+
+                if (backRequested)
+                {
+                    var backRequestedEventArgs = new RoutedEventArgs(BackRequestedEvent);
+                    RaiseEvent(backRequestedEventArgs);
+
+                    e.Handled = backRequestedEventArgs.Handled;
+                }
+            });
         }
 
         /// <summary>
@@ -263,6 +315,15 @@ namespace Avalonia.Controls
             set => SetValue(TransparencyBackgroundFallbackProperty, value);
         }
 
+        /// <summary>
+        /// Occurs when physical Back Button is pressed or a back navigation has been requested.
+        /// </summary>
+        public event EventHandler<RoutedEvent> BackRequested
+        {
+            add { AddHandler(BackRequestedEvent, value); }
+            remove { RemoveHandler(BackRequestedEvent, value); }
+        }
+
         public ILayoutManager LayoutManager
         {
             get
@@ -382,6 +443,7 @@ namespace Avalonia.Controls
 
             _pointerOverPreProcessor?.OnCompleted();
             _pointerOverPreProcessorSubscription?.Dispose();
+            _backGestureSubscription?.Dispose();
 
             PlatformImpl = null;
 

src/Browser/Avalonia.Browser/BrowserSystemNavigationManager.cs

@@ -0,0 +1,24 @@
+using System;
+using Avalonia.Browser.Interop;
+using Avalonia.Interactivity;
+using Avalonia.Platform;
+
+namespace Avalonia.Browser
+{
+    internal class BrowserSystemNavigationManager : ISystemNavigationManager
+    {
+        public event EventHandler<RoutedEventArgs>? BackRequested;
+
+        public BrowserSystemNavigationManager()
+        {
+            NavigationHelper.AddBackHandler(() =>
+            {
+                var routedEventArgs = new RoutedEventArgs();
+
+                BackRequested?.Invoke(this, routedEventArgs);
+
+                return routedEventArgs.Handled;
+            });
+        }
+    }
+}

src/Browser/Avalonia.Browser/BrowserTopLevelImpl.cs

@@ -19,7 +19,8 @@ using Avalonia.Rendering.Composition;
 
 namespace Avalonia.Browser
 {
-    internal class BrowserTopLevelImpl : ITopLevelImplWithTextInputMethod, ITopLevelImplWithNativeControlHost, ITopLevelImplWithStorageProvider
+    internal class BrowserTopLevelImpl : ITopLevelImplWithTextInputMethod, ITopLevelImplWithNativeControlHost, ITopLevelImplWithStorageProvider,
+        ITopLevelWithSystemNavigationManager
     {
         private Size _clientSize;
         private IInputRoot? _inputRoot;
@@ -239,5 +240,7 @@ namespace Avalonia.Browser
 
         public INativeControlHostImpl? NativeControlHost { get; }
         public IStorageProvider StorageProvider { get; } = new BrowserStorageProvider();
+
+        public ISystemNavigationManager SystemNavigationManager { get; } = new BrowserSystemNavigationManager();
     }
 }

src/Browser/Avalonia.Browser/Interop/NavigationHelper.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Runtime.InteropServices.JavaScript;
+
+namespace Avalonia.Browser.Interop;
+
+internal static partial class NavigationHelper
+{
+    [JSImport("NavigationHelper.addBackHandler", AvaloniaModule.MainModuleName)]
+    public static partial void AddBackHandler([JSMarshalAs<JSType.Function<JSType.Boolean>>] Func<bool> backHandlerCallback);
+}

src/Browser/Avalonia.Browser/webapp/modules/avalonia.ts

@@ -5,6 +5,7 @@ import { AvaloniaDOM } from "./avalonia/dom";
 import { Caniuse } from "./avalonia/caniuse";
 import { StreamHelper } from "./avalonia/stream";
 import { NativeControlHost } from "./avalonia/nativeControlHost";
+import { NavigationHelper } from "./avalonia/navigationHelper";
 
 async function registerAvaloniaModule(api: RuntimeAPI): Promise<void> {
     api.setModuleImports("avalonia", {
@@ -15,7 +16,8 @@ async function registerAvaloniaModule(api: RuntimeAPI): Promise<void> {
         DpiWatcher,
         AvaloniaDOM,
         StreamHelper,
-        NativeControlHost
+        NativeControlHost,
+        NavigationHelper
     });
 }
 export {
@@ -27,6 +29,7 @@ export {
     AvaloniaDOM,
     StreamHelper,
     NativeControlHost,
+    NavigationHelper,
 
     registerAvaloniaModule
 };

src/Browser/Avalonia.Browser/webapp/modules/avalonia/navigationHelper.ts

@@ -0,0 +1,14 @@
+export class NavigationHelper {
+    public static addBackHandler(backHandlerCallback: () => Boolean) {
+        history.pushState(null, "", window.location.href);
+        window.onpopstate = () => {
+            const handled = backHandlerCallback();
+
+            if (!handled) {
+                history.back();
+            } else {
+                history.forward();
+            }
+        };
+    }
+}