Fix Launcher focus for most cases (#4362)

* Add SendInput hack

* Cleaned up code

* Fixed formatting

* Moved Activate fn call

* Add more comments with link to issue

src/modules/launcher/PowerLauncher/MainWindow.xaml.cs

@@ -64,6 +64,17 @@ namespace PowerLauncher
             _viewModel.Save();
         }
 
+        private void BringProcessToForeground()
+        {
+            // Use SendInput hack to allow Activate to work - required to resolve focus issue https://github.com/microsoft/PowerToys/issues/4270
+            WindowsInteropHelper.INPUT input = new WindowsInteropHelper.INPUT { type = WindowsInteropHelper.INPUTTYPE.INPUT_MOUSE, data = { } };
+            WindowsInteropHelper.INPUT[] inputs = new WindowsInteropHelper.INPUT[] { input };
+
+            // Send empty mouse event. This makes this thread the last to send input, and hence allows it to pass foreground permission checks
+            WindowsInteropHelper.SendInput(1, inputs, WindowsInteropHelper.INPUT.Size);
+            Activate();
+        }
+
         private void OnLoaded(object sender, RoutedEventArgs _)
         {
             WindowsInteropHelper.DisableControlBox(this);
@@ -79,7 +90,7 @@ namespace PowerLauncher
             ListBox.SuggestionsList.PreviewMouseLeftButtonUp += SuggestionsList_PreviewMouseLeftButtonUp;
             _viewModel.PropertyChanged += ViewModel_PropertyChanged;
 
-            Activate();
+            BringProcessToForeground();
         }
 
         private void SuggestionsList_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
@@ -105,7 +116,7 @@ namespace PowerLauncher
                 // Not called on first launch
                 // Additionally called when deactivated by clicking on screen  
                 UpdatePosition();
-                Activate();
+                BringProcessToForeground();
 
                 if (!_viewModel.LastQuerySelected)
                 {

src/modules/launcher/Wox/Helper/WindowsInteropHelper.cs

@@ -34,6 +34,68 @@ namespace Wox.Helper
             }
         }
 
+        [DllImport("user32.dll")]
+        public static extern uint SendInput(uint nInputs, INPUT[] pInputs, int cbSize);
+
+        [StructLayout(LayoutKind.Sequential)]
+        public struct INPUT
+        {
+            public INPUTTYPE type;
+            public InputUnion data;
+
+            public static int Size
+            {
+                get { return Marshal.SizeOf(typeof(INPUT)); }
+            }
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        public struct InputUnion
+        {
+            [FieldOffset(0)]
+            internal MOUSEINPUT mi;
+            [FieldOffset(0)]
+            internal KEYBDINPUT ki;
+            [FieldOffset(0)]
+            internal HARDWAREINPUT hi;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        internal struct MOUSEINPUT
+        {
+            internal int dx;
+            internal int dy;
+            internal int mouseData;
+            internal uint dwFlags;
+            internal uint time;
+            internal UIntPtr dwExtraInfo;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        internal struct KEYBDINPUT
+        {
+            internal short wVk;
+            internal short wScan;
+            internal uint dwFlags;
+            internal int time;
+            internal UIntPtr dwExtraInfo;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        internal struct HARDWAREINPUT
+        {
+            internal int uMsg;
+            internal short wParamL;
+            internal short wParamH;
+        }
+
+        public enum INPUTTYPE : uint
+        {
+            INPUT_MOUSE = 0,
+            INPUT_KEYBOARD = 1,
+            INPUT_HARDWARE = 2,
+        }
+
         [DllImport("user32.dll", SetLastError = true)]
         private static extern int GetWindowLong(IntPtr hWnd, int nIndex);