Merge pull request #41 from mgnslndh/webview2-movefocus-crash

Fix WebView2 MoveFocus crash on window activation (issue #27)

Author: maxkatz6

src/Avalonia.Controls.WebView.Core/Win/WebView2/WebView2BaseAdapter.cs

@@ -245,11 +245,44 @@ private Task<Stream> PrintToPdfStreamAsyncInternal(WebViewPrintSettings? setting
 
     public void Focus()
     {
-        controller.MoveFocus(0 /* Programmatic */);
+        SafeCallController(() =>
+            controller.MoveFocus(COREWEBVIEW2_MOVE_FOCUS_REASON.COREWEBVIEW2_MOVE_FOCUS_REASON_PROGRAMMATIC));
     }
 
     public void ResignFocus() { }
 
+    private void SafeCallController(Action action)
+    {
+        if (Disposed || controller == null)
+        {
+            return;
+        }
+        try
+        {
+            action();
+        }
+        catch (ArgumentException ex) when (ex.HResult == HResult.EInvalidArg)
+        {
+            // Controller rejected MoveFocus with E_INVALIDARG — transient state during
+            // async init or window-activation race. Safe to ignore; focus re-establishes
+            // naturally once the controller reaches a ready state.
+        }
+        catch (COMException ex) when (ex.HResult is HResult.EInvalidArg or HResult.EInvalidState)
+        {
+            // Same transient rejection surfaced as COMException depending on the
+            // source-generated interop path (e.g. during controller teardown).
+        }
+    }
+
+    private static class HResult
+    {
+        // E_INVALIDARG (0x80070057): returned by MoveFocus when the controller rejects
+        // the call during async init or window-activation races.
+        public const int EInvalidArg = unchecked((int)0x80070057);
+        // ERROR_INVALID_STATE (0x8007139F): observed in teardown-phase rejections.
+        public const int EInvalidState = unchecked((int)0x8007139F);
+    }
+
     internal EventHandler<WebViewNavigationStartingEventArgs>? GetNavigationStarted() => NavigationStarted;
     internal EventHandler<WebViewNavigationCompletedEventArgs>? GetNavigationCompleted() => NavigationCompleted;
     internal EventHandler<WebMessageReceivedEventArgs>? GetWebMessageReceived() => WebMessageReceived;

tests/Avalonia.Controls.WebView.Tests/WebView2BaseAdapterTests.cs

@@ -0,0 +1,74 @@
+#pragma warning disable CA1416 // Platform compatibility — guarded by runtime OS check inside each test
+
+using System;
+using System.Runtime.InteropServices;
+using Avalonia.Controls.Win;
+using Avalonia.Controls.Win.WebView2;
+using Avalonia.Controls.Win.WebView2.Interop;
+using Xunit;
+
+namespace Avalonia.Controls.WebView.Tests;
+
+public class WebView2BaseAdapterTests
+{
+    // Reproduces https://github.com/AvaloniaUI/Avalonia.Controls.WebView/issues/27
+    // The controller exists but rejects MoveFocus with E_INVALIDARG during a
+    // window-activation race (WM_ACTIVATE fires before async init completes).
+    // This tests that the adapter's Focus method doesn't throw in this scenario, which would cause a crash at runtime.
+    // NOTE: This is a regression test for a specific issue. We test the implementation by faking the behavior
+    // of the controller, rather than using a real WebView2 instance, to avoid the complexity of reproducing the exact race
+    // condition in a reliable way.
+    [Fact]
+    public void FocusShouldNotThrowWhenControllerThrowsEInvalidArg()
+    {
+        if (!OperatingSystem.IsWindows())
+        {
+            Assert.Skip("WebView2 adapter is Windows-only");
+        }
+
+        var adapter = new TestableAdapter(new ThrowingFakeController());
+        
+        adapter.Focus();
+    }
+
+    private sealed class TestableAdapter(ICoreWebView2Controller controller)
+        : WebView2BaseAdapter(controller)
+    {
+        public override IntPtr Handle => IntPtr.Zero;
+        public override string? HandleDescriptor => null;
+    }
+
+    private sealed class ThrowingFakeController : ICoreWebView2Controller
+    {
+        void ICoreWebView2Controller.MoveFocus(COREWEBVIEW2_MOVE_FOCUS_REASON reason)
+        {
+            // Marshal.GetExceptionForHR produces the exact ArgumentException with HResult
+            // E_INVALIDARG that the source-generated COM interop layer throws at runtime.
+            throw (ArgumentException)Marshal.GetExceptionForHR(unchecked((int)0x80070057))!;
+        }
+
+        void ICoreWebView2Controller.Close() { }
+
+        int ICoreWebView2Controller.GetIsVisible() => throw new NotImplementedException();
+        void ICoreWebView2Controller.SetIsVisible(int value) => throw new NotImplementedException();
+        tagRECT ICoreWebView2Controller.GetBounds() => throw new NotImplementedException();
+        void ICoreWebView2Controller.SetBounds(tagRECT value) => throw new NotImplementedException();
+        double ICoreWebView2Controller.GetZoomFactor() => throw new NotImplementedException();
+        void ICoreWebView2Controller.SetZoomFactor(double value) => throw new NotImplementedException();
+        void ICoreWebView2Controller.add_ZoomFactorChanged(IntPtr eventHandler, out EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.remove_ZoomFactorChanged(EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.SetBoundsAndZoomFactor(tagRECT bounds, double zoomFactor) => throw new NotImplementedException();
+        void ICoreWebView2Controller.add_MoveFocusRequested(ICoreWebView2MoveFocusRequestedEventHandler eventHandler, out EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.remove_MoveFocusRequested(EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.add_GotFocus(ICoreWebView2FocusChangedEventHandler eventHandler, out EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.remove_GotFocus(EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.add_LostFocus(ICoreWebView2FocusChangedEventHandler eventHandler, out EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.remove_LostFocus(EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.add_AcceleratorKeyPressed(IntPtr eventHandler, out EventRegistrationToken token) => throw new NotImplementedException();
+        void ICoreWebView2Controller.remove_AcceleratorKeyPressed(EventRegistrationToken token) => throw new NotImplementedException();
+        IntPtr ICoreWebView2Controller.GetParentWindow() => throw new NotImplementedException();
+        void ICoreWebView2Controller.SetParentWindow(IntPtr value) => throw new NotImplementedException();
+        void ICoreWebView2Controller.NotifyParentWindowPositionChanged() => throw new NotImplementedException();
+        ICoreWebView2 ICoreWebView2Controller.GetCoreWebView2() => throw new NotImplementedException();
+    }
+}