Add WinForms message filter for Avalonia windows (#20814)

* Add WinForms message filter for Avalonia windows

* Do not use filter messages for WinFormsAvaloniaControlHost

samples/interop/WindowsInteropTest/EmbedToWinFormsDemo.Designer.cs

@@ -30,87 +30,88 @@ namespace WindowsInteropTest
         /// </summary>
         private void InitializeComponent()
         {
-            this.button1 = new System.Windows.Forms.Button();
-            this.monthCalendar1 = new System.Windows.Forms.MonthCalendar();
-            this.groupBox1 = new System.Windows.Forms.GroupBox();
-            this.groupBox2 = new System.Windows.Forms.GroupBox();
-            this.avaloniaHost = new WinFormsAvaloniaControlHost();
-            this.groupBox1.SuspendLayout();
-            this.groupBox2.SuspendLayout();
-            this.SuspendLayout();
-            // 
-            // button1
-            // 
-            this.button1.Location = new System.Drawing.Point(28, 29);
-            this.button1.Name = "button1";
-            this.button1.Size = new System.Drawing.Size(164, 73);
-            this.button1.TabIndex = 0;
-            this.button1.Text = "button1";
-            this.button1.UseVisualStyleBackColor = true;
-            // 
+            OpenWindowButton = new System.Windows.Forms.Button();
+            monthCalendar1 = new System.Windows.Forms.MonthCalendar();
+            groupBox1 = new System.Windows.Forms.GroupBox();
+            groupBox2 = new System.Windows.Forms.GroupBox();
+            avaloniaHost = new Avalonia.Win32.Interoperability.WinFormsAvaloniaControlHost();
+            groupBox1.SuspendLayout();
+            groupBox2.SuspendLayout();
+            SuspendLayout();
+            //
+            // OpenWindowButton
+            //
+            OpenWindowButton.Location = new System.Drawing.Point(33, 33);
+            OpenWindowButton.Margin = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            OpenWindowButton.Name = "OpenWindowButton";
+            OpenWindowButton.Size = new System.Drawing.Size(191, 84);
+            OpenWindowButton.TabIndex = 0;
+            OpenWindowButton.Text = "Open Avalonia Window";
+            OpenWindowButton.UseVisualStyleBackColor = true;
+            OpenWindowButton.Click += OpenWindowButton_Click;
+            //
             // monthCalendar1
-            // 
-            this.monthCalendar1.Location = new System.Drawing.Point(28, 114);
-            this.monthCalendar1.Name = "monthCalendar1";
-            this.monthCalendar1.TabIndex = 1;
-            // 
+            //
+            monthCalendar1.Location = new System.Drawing.Point(33, 132);
+            monthCalendar1.Margin = new System.Windows.Forms.Padding(10);
+            monthCalendar1.Name = "monthCalendar1";
+            monthCalendar1.TabIndex = 1;
+            //
             // groupBox1
-            // 
-            this.groupBox1.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
-            | System.Windows.Forms.AnchorStyles.Left)));
-            this.groupBox1.Controls.Add(this.button1);
-            this.groupBox1.Controls.Add(this.monthCalendar1);
-            this.groupBox1.Location = new System.Drawing.Point(12, 12);
-            this.groupBox1.Name = "groupBox1";
-            this.groupBox1.Size = new System.Drawing.Size(227, 418);
-            this.groupBox1.TabIndex = 2;
-            this.groupBox1.TabStop = false;
-            this.groupBox1.Text = "WinForms";
-            // 
+            //
+            groupBox1.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) | System.Windows.Forms.AnchorStyles.Left));
+            groupBox1.Controls.Add(OpenWindowButton);
+            groupBox1.Controls.Add(monthCalendar1);
+            groupBox1.Location = new System.Drawing.Point(14, 14);
+            groupBox1.Margin = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            groupBox1.Name = "groupBox1";
+            groupBox1.Padding = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            groupBox1.Size = new System.Drawing.Size(265, 482);
+            groupBox1.TabIndex = 2;
+            groupBox1.TabStop = false;
+            groupBox1.Text = "WinForms";
+            //
             // groupBox2
-            // 
-            this.groupBox2.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
-            | System.Windows.Forms.AnchorStyles.Left) 
-            | System.Windows.Forms.AnchorStyles.Right)));
-            this.groupBox2.Controls.Add(this.avaloniaHost);
-            this.groupBox2.Location = new System.Drawing.Point(245, 12);
-            this.groupBox2.Name = "groupBox2";
-            this.groupBox2.Size = new System.Drawing.Size(501, 418);
-            this.groupBox2.TabIndex = 3;
-            this.groupBox2.TabStop = false;
-            this.groupBox2.Text = "Avalonia";
-            // 
+            //
+            groupBox2.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) | System.Windows.Forms.AnchorStyles.Left) | System.Windows.Forms.AnchorStyles.Right));
+            groupBox2.Controls.Add(avaloniaHost);
+            groupBox2.Location = new System.Drawing.Point(286, 14);
+            groupBox2.Margin = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            groupBox2.Name = "groupBox2";
+            groupBox2.Padding = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            groupBox2.Size = new System.Drawing.Size(584, 482);
+            groupBox2.TabIndex = 3;
+            groupBox2.TabStop = false;
+            groupBox2.Text = "Avalonia";
+            //
             // avaloniaHost
-            // 
-            this.avaloniaHost.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
-            | System.Windows.Forms.AnchorStyles.Left) 
-            | System.Windows.Forms.AnchorStyles.Right)));
-            this.avaloniaHost.Content = null;
-            this.avaloniaHost.Location = new System.Drawing.Point(6, 19);
-            this.avaloniaHost.Name = "avaloniaHost";
-            this.avaloniaHost.Size = new System.Drawing.Size(489, 393);
-            this.avaloniaHost.TabIndex = 0;
-            this.avaloniaHost.Text = "avaloniaHost";
-            // 
+            //
+            avaloniaHost.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) | System.Windows.Forms.AnchorStyles.Left) | System.Windows.Forms.AnchorStyles.Right));
+            avaloniaHost.Location = new System.Drawing.Point(7, 22);
+            avaloniaHost.Margin = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            avaloniaHost.Name = "avaloniaHost";
+            avaloniaHost.Size = new System.Drawing.Size(570, 453);
+            avaloniaHost.TabIndex = 0;
+            avaloniaHost.Text = "avaloniaHost";
+            //
             // EmbedToWinFormsDemo
-            // 
-            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
-            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
-            this.ClientSize = new System.Drawing.Size(758, 442);
-            this.Controls.Add(this.groupBox2);
-            this.Controls.Add(this.groupBox1);
-            this.MinimumSize = new System.Drawing.Size(600, 400);
-            this.Name = "EmbedToWinFormsDemo";
-            this.Text = "EmbedToWinFormsDemo";
-            this.groupBox1.ResumeLayout(false);
-            this.groupBox2.ResumeLayout(false);
-            this.ResumeLayout(false);
-
+            //
+            AutoScaleDimensions = new System.Drawing.SizeF(7F, 15F);
+            AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
+            ClientSize = new System.Drawing.Size(884, 510);
+            Controls.Add(groupBox2);
+            Controls.Add(groupBox1);
+            Margin = new System.Windows.Forms.Padding(4, 3, 4, 3);
+            MinimumSize = new System.Drawing.Size(697, 456);
+            Text = "EmbedToWinFormsDemo";
+            groupBox1.ResumeLayout(false);
+            groupBox2.ResumeLayout(false);
+            ResumeLayout(false);
         }
 
         #endregion
 
-        private System.Windows.Forms.Button button1;
+        private System.Windows.Forms.Button OpenWindowButton;
         private System.Windows.Forms.MonthCalendar monthCalendar1;
         private System.Windows.Forms.GroupBox groupBox1;
         private System.Windows.Forms.GroupBox groupBox2;

samples/interop/WindowsInteropTest/EmbedToWinFormsDemo.cs

@@ -1,5 +1,10 @@
-using System.Windows.Forms;
+using System;
+using System.Windows.Forms;
 using ControlCatalog;
+using AvaloniaButton = Avalonia.Controls.Button;
+using AvaloniaStackPanel = Avalonia.Controls.StackPanel;
+using AvaloniaTextBox = Avalonia.Controls.TextBox;
+using AvaloniaWindow = Avalonia.Controls.Window;
 
 namespace WindowsInteropTest
 {
@@ -10,5 +15,23 @@ namespace WindowsInteropTest
             InitializeComponent();
             avaloniaHost.Content = new MainView();
         }
+
+        private void OpenWindowButton_Click(object sender, EventArgs e)
+        {
+            var window = new AvaloniaWindow
+            {
+                Width = 300,
+                Height = 300,
+                Content = new AvaloniaStackPanel
+                {
+                    Children =
+                    {
+                        new AvaloniaButton { Content = "Button" },
+                        new AvaloniaTextBox { Text = "Text" }
+                    }
+                }
+            };
+            window.Show();
+        }
     }
 }

samples/interop/WindowsInteropTest/Program.cs

@@ -1,6 +1,7 @@
 using System;
 using ControlCatalog;
 using Avalonia;
+using Avalonia.Win32.Interoperability;
 
 namespace WindowsInteropTest
 {
@@ -14,9 +15,11 @@ namespace WindowsInteropTest
         {
             System.Windows.Forms.Application.EnableVisualStyles();
             System.Windows.Forms.Application.SetCompatibleTextRenderingDefault(false);
+            System.Windows.Forms.Application.AddMessageFilter(new WinFormsAvaloniaMessageFilter());
             AppBuilder.Configure<App>()
                 .UseWin32()
                 .UseSkia()
+                .UseHarfBuzz()
                 .SetupWithoutStarting();
             System.Windows.Forms.Application.Run(new EmbedToWinFormsDemo());
         }

samples/interop/WindowsInteropTest/WindowsInteropTest.csproj

@@ -8,6 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\..\..\src\HarfBuzz\Avalonia.HarfBuzz\Avalonia.HarfBuzz.csproj" />
     <ProjectReference Include="..\..\..\src\Skia\Avalonia.Skia\Avalonia.Skia.csproj" />
     <ProjectReference Include="..\..\..\src\Windows\Avalonia.Win32.Interoperability\Avalonia.Win32.Interoperability.csproj" />
     <ProjectReference Include="..\..\ControlCatalog\ControlCatalog.csproj" />

src/Windows/Avalonia.Win32.Interoperability/WinForms/WinFormsAvaloniaMessageFilter.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Windows.Forms;
+using static Avalonia.Win32.Interop.UnmanagedMethods;
+
+namespace Avalonia.Win32.Interoperability;
+
+/// <summary>
+/// Provides a message filter for integrating Avalonia within a WinForms application.
+/// </summary>
+/// <remarks>
+/// This filter ensures that key messages, which are typically handled specially by WinForms,
+/// are intercepted and routed to Avalonia's windows. This is necessary to preserve proper input handling
+/// in mixed WinForms and Avalonia application scenarios.
+/// </remarks>
+public class WinFormsAvaloniaMessageFilter : IMessageFilter
+{
+    /// <inheritdoc />
+    public bool PreFilterMessage(ref Message m)
+    {
+        // WinForms handles key messages specially, preventing them from reaching Avalonia's windows.
+        // Handle them first.
+        if (m.Msg >= (int)WindowsMessage.WM_KEYFIRST &&
+            m.Msg <= (int)WindowsMessage.WM_KEYLAST &&
+            WindowImpl.IsOurWindowGlobal(m.HWnd) &&
+            !IsInsideWinForms(m.HWnd))
+        {
+            var msg = new MSG
+            {
+                hwnd = m.HWnd,
+                message = (uint)m.Msg,
+                wParam = m.WParam,
+                lParam = m.LParam
+            };
+
+            TranslateMessage(ref msg);
+            DispatchMessage(ref msg);
+            return true;
+        }
+
+        return false;
+    }
+
+    private static bool IsInsideWinForms(IntPtr hwnd)
+    {
+        var parentHwnd = GetParent(hwnd);
+        return parentHwnd != IntPtr.Zero && Control.FromHandle(parentHwnd) is WinFormsAvaloniaControlHost;
+    }
+}

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -1004,6 +1004,14 @@ namespace Avalonia.Win32
             if (hwnd == _hwnd)
                 return true;
 
+            return IsOurWindowGlobal(hwnd);
+        }
+
+        internal static bool IsOurWindowGlobal(IntPtr hwnd)
+        {
+            if (hwnd == IntPtr.Zero)
+                return false;
+
             lock (s_instances)
                 for (int i = 0; i < s_instances.Count; i++)
                     if (s_instances[i]._hwnd == hwnd)