HotKey.cs

public sealed class HotKey : IDisposable
{
    private readonly IntPtr _handle;

    private readonly int _id;

    private bool _isKeyRegistered;

    public HotKey(ModifierKeys modifierKeys, Key key, Window window)
        : this(modifierKeys, key, new WindowInteropHelper(window))
    {
    }

    public HotKey(ModifierKeys modifierKeys, Key key, WindowInteropHelper window)
        : this(modifierKeys, key, window.Handle)
    {
    }

    public HotKey(ModifierKeys modifierKeys, Key key, IntPtr windowHandle)
    {
        Key = key;
        KeyModifier = modifierKeys;
        _id = GetHashCode();
        _handle = windowHandle;
        RegisterHotKey();
        ComponentDispatcher.ThreadPreprocessMessage += ThreadPreprocessMessageMethod;
    }

    ~HotKey()
    {
        Dispose();
    }

    public event Action<HotKey> HotKeyPressed;

    public Key Key { get; private set; }

    public ModifierKeys KeyModifier { get; private set; }

    private int InteropKey
    {
        get
        {
            return KeyInterop.VirtualKeyFromKey(Key);
        }
    }

    public void Dispose()
    {
        ComponentDispatcher.ThreadPreprocessMessage -= ThreadPreprocessMessageMethod;
        UnregisterHotKey();
    }

    private void OnHotKeyPressed()
    {
        if (HotKeyPressed != null)
        {
            HotKeyPressed(this);
        }
    }

    private void RegisterHotKey()
    {
        if (Key == Key.None)
        {
            return;
        }

        if (_isKeyRegistered)
        {
            UnregisterHotKey();
        }

        _isKeyRegistered = HotKeyWinApi.RegisterHotKey(_handle, _id, KeyModifier, InteropKey);

        if (!_isKeyRegistered)
        {
            throw new ApplicationException("Hotkey already in use");
        }
    }

    private void ThreadPreprocessMessageMethod(ref MSG msg, ref bool handled)
    {
        if (handled)
        {
            return;
        }

        if (msg.message != HotKeyWinApi.WmHotKey || (int)(msg.wParam) != _id)
        {
            return;
        }

        OnHotKeyPressed();
        handled = true;
    }

    private void UnregisterHotKey()
    {
        _isKeyRegistered = !HotKeyWinApi.UnregisterHotKey(_handle, _id);
    }
}

HotKeyWinApi.cs

public class HotKeyWinApi
{
    public const int WmHotKey = 0x0312;

    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool RegisterHotKey(IntPtr hWnd, int id, ModifierKeys fsModifiers, int vk);

    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool UnregisterHotKey(IntPtr hWnd, int id);
}