Register hotkey in system for WPF application
Couple days ago I got a question about how to register hotkey in Windows for WPF application. I remembered that one year ago I was solving the same problem in WinForms application, I was registering hot keys for my application, it was Vista Keys Extender project. I knew that my project worked, so I suggested author of question to use code of my project to solve his problem. But as we learned later in WPF message handle mechanism different from WinForms. So I started to find solution for WPF application. I copied my old code from my old project and started to rewrite it step-by-step.
First off all we need to import WinAPI methods:
internal class HotKeyWinApi
{
public const int WmHotKey = 0x0312;
[DllImport("user32.dll", SetLastError = true)]
public static extern bool RegisterHotKey(IntPtr hWnd, int id, ModifierKeys fsModifiers, Keys vk);
[DllImport("user32.dll", SetLastError = true)]
public static extern bool UnregisterHotKey(IntPtr hWnd, int id);
}
In Vista Keys Extender project I implemented own enum KeyModifiers, but in WPF I don’t need to do this, because it has System.Windows.Input.ModifierKeys, which equals to my own enum. Also in my old project I used System.Windows.Forms.Keys, but in WPF enum System.Windows.Input.Key different, it has other values. I didn’t want to set reference from my new WPF project to assembly System.Windows.Forms, because I need just one enum. So I copied this enum from assembly to my new WPF project. Ok, so I did all preparations and now I need to realize main class HotKey:
public sealed class HotKey : IDisposable
{
public event Action<HotKey> HotKeyPressed;
private readonly int _id;
private bool _isKeyRegistered;
readonly IntPtr _handle;
public HotKey(ModifierKeys modifierKeys, Keys key, Window window)
: this (modifierKeys, key, new WindowInteropHelper(window))
{
Contract.Requires(window != null);
}
public HotKey(ModifierKeys modifierKeys, Keys key, WindowInteropHelper window)
: this(modifierKeys, key, window.Handle)
{
Contract.Requires(window != null);
}
public HotKey(ModifierKeys modifierKeys, Keys key, IntPtr windowHandle)
{
Contract.Requires(modifierKeys != ModifierKeys.None || key != Keys.None);
Contract.Requires(windowHandle != IntPtr.Zero);
Key = key;
KeyModifier = modifierKeys;
_id = GetHashCode();
_handle = windowHandle;
RegisterHotKey();
ComponentDispatcher.ThreadPreprocessMessage += ThreadPreprocessMessageMethod;
}
~HotKey()
{
Dispose();
}
public Keys Key { get; private set; }
public ModifierKeys KeyModifier { get; private set; }
public void RegisterHotKey()
{
if (Key == Keys.None)
return;
if (_isKeyRegistered)
UnregisterHotKey();
_isKeyRegistered = HotKeyWinApi.RegisterHotKey(_handle, _id, KeyModifier, Key);
if (!_isKeyRegistered)
throw new ApplicationException("Hotkey already in use");
}
public void UnregisterHotKey()
{
_isKeyRegistered = !HotKeyWinApi.UnregisterHotKey(_handle, _id);
}
public void Dispose()
{
ComponentDispatcher.ThreadPreprocessMessage -= ThreadPreprocessMessageMethod;
UnregisterHotKey();
}
private void ThreadPreprocessMessageMethod(ref MSG msg, ref bool handled)
{
if (!handled)
{
if (msg.message == HotKeyWinApi.WmHotKey
&& (int)(msg.wParam) == _id)
{
OnHotKeyPressed();
handled = true;
}
}
}
private void OnHotKeyPressed()
{
if (HotKeyPressed != null)
HotKeyPressed(this);
}
}
And small sample of using:
public partial class MainWindow : Window
{
private HotKey _hotkey;
public MainWindow()
{
InitializeComponent();
Loaded += (s, e) =>
{
_hotkey = new HotKey(ModifierKeys.Windows | ModifierKeys.Alt, Keys.Left, this);
_hotkey.HotKeyPressed += (k) => Console.Beep();
};
}
}
You can look and download source code of this sample from my public SVN repository at assembla.