fix(wasm): key tracking when no one is subscribing to Key<Down|Up>

src/Uno.UI/ts/WindowManager.ts

@@ -133,6 +133,7 @@ namespace Uno.UI {
 		private static dispatchSuspendingMethod: any;
 		private static getDependencyPropertyValueMethod: any;
 		private static setDependencyPropertyValueMethod: any;
+		private static keyTrackingMethod: any;
 
 		private constructor(private containerElementId: string, private loadingElementId: string) {
 			this.initDom();
@@ -1437,6 +1438,7 @@ namespace Uno.UI {
 				WindowManager.dispatchEventMethod = exports.Microsoft.UI.Xaml.UIElement.DispatchEvent;
 				WindowManager.focusInMethod = exports.Microsoft.UI.Xaml.Input.FocusManager.ReceiveFocusNative;
 				WindowManager.dispatchSuspendingMethod = exports.Microsoft.UI.Xaml.Application.DispatchSuspending;
+				WindowManager.keyTrackingMethod = (<any>globalThis).DotnetExports.Uno.Uno.UI.Core.KeyboardStateTracker.UpdateKeyStateNative;
 			} else {
 				throw `Unable to find dotnet exports`;
 			}
@@ -1451,6 +1453,13 @@ namespace Uno.UI {
 			document.body.addEventListener("focusin", this.onfocusin);
 			document.body.appendChild(this.containerElement);
 
+			// On WASM, if no one subscribes to key<Down|Up>, not only will the event not fire on any UIElement,
+			// but the browser won't even notify us that a key was pressed/released, and this breaks KeyboardStateTracker
+			// key tracking, which depends on RaiseEvent being called even if no one is subscribing. Instead, we
+			// subscribe on the body and make sure to call KeyboardStateTracker ourselves here.
+			document.body.addEventListener("keydown", this.onBodyKeyDown);
+			document.body.addEventListener("keyup", this.onBodyKeyUp);
+
 			window.addEventListener("resize", x => WindowManager.resize());
 			window.addEventListener("contextmenu", x => {
 				if (!(x.target instanceof HTMLInputElement) ||
@@ -1593,6 +1602,14 @@ namespace Uno.UI {
 		public moveWindow(x: number, y: number) {
 			window.moveTo(x, y);
 		}
+
+		private onBodyKeyDown(event: KeyboardEvent) {
+			WindowManager.keyTrackingMethod(event.key, true);
+		}
+
+		private onBodyKeyUp(event: KeyboardEvent) {
+			WindowManager.keyTrackingMethod(event.key, false);
+		}
 	}
 
 	if (typeof define === "function") {

src/Uno.UWP/UI/Core/Internal/KeyboardStateTracker.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.InteropServices.JavaScript;
 using Windows.System;
 using Windows.UI.Core;
 
@@ -13,7 +14,7 @@ namespace Uno.UI.Core;
 ///	In UWP/WinUI, every key has a locked state (not only Caps Lock, etc.). The sequence of states is as follows:
 ///	(None) -> (Down) -> (None) -> (Down + Locked) -> (None + Locked) -> (Down) -> (None) -> etc.
 /// </remarks>
-internal static class KeyboardStateTracker
+internal static partial class KeyboardStateTracker
 {
 	private static readonly Dictionary<VirtualKey, CoreVirtualKeyStates> _keyStates = new Dictionary<VirtualKey, CoreVirtualKeyStates>();
 
@@ -106,4 +107,21 @@ internal static void Reset()
 			_keyStates.Clear();
 		}
 	}
+
+#if __WASM__
+#pragma warning disable IDE0051 // Remove unused private members
+	[JSExport]
+	private static void UpdateKeyStateNative(string key, bool down)
+#pragma warning restore IDE0051 // Remove unused private members
+	{
+		if (down)
+		{
+			OnKeyDown(VirtualKeyHelper.FromKey(key));
+		}
+		else
+		{
+			OnKeyUp(VirtualKeyHelper.FromKey(key));
+		}
+	}
+#endif
 }