Merge pull request #4149 from icsharpcode/fix/4143-taskbar-icon

Re-send the window icon after a theme flip or resume

ILSpy.Tests/MainWindow/MainWindowTests.cs

@@ -60,6 +60,26 @@ public class MainWindowTests
 		window.DataContext.Should().BeOfType<MainWindowViewModel>();
 	}
 
+	[AvaloniaTest]
+	public void ReapplyWindowIcon_Hands_The_Platform_A_New_Icon_Instance()
+	{
+		// The platform window ignores an Icon assignment of the instance it already holds, so
+		// re-sending the icon to the OS taskbar only works with a fresh WindowIcon.
+
+		// Arrange
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+		var before = window.Icon;
+		before.Should().NotBeNull();
+
+		// Act
+		window.ReapplyWindowIcon();
+
+		// Assert
+		window.Icon.Should().NotBeNull();
+		window.Icon.Should().NotBeSameAs(before);
+	}
+
 	[AvaloniaTest]
 	public async Task Assembly_Tree_Pane_Is_Visible_In_Layout()
 	{

ILSpy/Views/MainWindow.axaml.cs

@@ -16,13 +16,17 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System;
 using System.ComponentModel;
 using System.Composition;
+using System.Runtime.InteropServices;
 
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Interactivity;
+using Avalonia.Platform;
+using Avalonia.Threading;
 
 using ICSharpCode.ILSpy.AppEnv;
 using ICSharpCode.ILSpy.ViewModels;
@@ -80,6 +84,8 @@ namespace ICSharpCode.ILSpy.Views
 			AddHandler(PointerReleasedEvent, OnBrowserNavigationPointerReleased,
 				RoutingStrategies.Bubble, handledEventsToo: true);
 			ApplySessionSettings(settingsService.SessionSettings);
+			if (OperatingSystem.IsWindows())
+				Win32Properties.AddWndProcHookCallback(this, TaskbarIconWndProcHook);
 			Opened += async (_, _) => {
 				AppLog.Mark("MainWindow.Opened fired");
 				using (AppLog.Phase("AssemblyTreeModel.Initialize"))
@@ -140,6 +146,42 @@ namespace ICSharpCode.ILSpy.Views
 			}
 		}
 
+		const uint WM_SETTINGCHANGE = 0x001A;
+		const uint WM_POWERBROADCAST = 0x0218;
+		const int PBT_APMRESUMEAUTOMATIC = 0x12;
+
+		bool windowIconRefreshPending;
+
+		// The Windows taskbar re-queries window icons when the system theme flips. A query that
+		// arrives while the UI thread is not pumping messages (typically right after resume from
+		// hibernate, which is also when a scheduled light/dark switch fires) goes unanswered, and
+		// the taskbar button stays blank because nothing prompts the taskbar to ask again.
+		// These messages are only dispatched once the thread pumps again, so re-sending the icon
+		// shortly afterwards repairs the button. The delay coalesces the burst of
+		// ImmersiveColorSet broadcasts a single theme flip produces.
+		IntPtr TaskbarIconWndProcHook(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam, ref bool handled)
+		{
+			bool iconMayBeLost = (msg == WM_POWERBROADCAST && wParam == PBT_APMRESUMEAUTOMATIC)
+				|| (msg == WM_SETTINGCHANGE && Marshal.PtrToStringUni(lParam) == "ImmersiveColorSet");
+			if (iconMayBeLost && !windowIconRefreshPending)
+			{
+				windowIconRefreshPending = true;
+				DispatcherTimer.RunOnce(() => {
+					windowIconRefreshPending = false;
+					ReapplyWindowIcon();
+				}, TimeSpan.FromSeconds(2));
+			}
+			return IntPtr.Zero;
+		}
+
+		// The platform window ignores an assignment of the WindowIcon instance it already holds,
+		// so re-sending the icon to the OS requires a new instance.
+		internal void ReapplyWindowIcon()
+		{
+			using var stream = AssetLoader.Open(new Uri("avares://ILSpy/Assets/ILSpy.ico"));
+			Icon = new WindowIcon(stream);
+		}
+
 		void ApplySessionSettings(SessionSettings session)
 		{
 			Position = session.WindowPosition;