Change the key being pressed with C#

Question

Hey, I'm trying to write a program in C# that will track the pressing of certain keys (using a keyboard hook), and send different ones instead.

For instance, when I press the A key it will instead send the Q key.

I used http://www.codeproject.com/KB/cs/CSLLKeyboardHook.aspx this for my hooks and tried to use the SendKeys function, but I get an exception about the garbage collector destroying some object inside the hook class.

Answer 1

First you need to hook up the keys.

With this class you can register a global shortcut, I'm skipping the explanation, but you can read it here.

public class KeyboardHook
{
    [DllImport("user32.dll")]
    private static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vk);

    [DllImport("user32.dll")]
    private static extern bool UnregisterHotKey(IntPtr hWnd, int id);

    public enum Modifiers
    {
        None = 0x0000,
        Alt = 0x0001,
        Control = 0x0002,
        Shift = 0x0004,
        Win = 0x0008
    }

    int modifier;
    int key;
    IntPtr hWnd;
    int id;

    public KeyboardHook(int modifiers, Keys key, Form f)
    {
        this.modifier = modifiers;
        this.key = (int)key;
        this.hWnd = f.Handle;
        id = this.GetHashCode();
    }

    public override int GetHashCode()
    {
        return modifier ^ key ^ hWnd.ToInt32();
    }


    public bool Register()
    {
        return RegisterHotKey(hWnd, id, modifier, key);
    }
    public bool Unregister()
    {
        return UnregisterHotKey(hWnd, id);
    }
}

Then on your form you have to register the shortcut

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        KeyboardHook hook = new KeyboardHook((int)KeyboardHook.Modifiers.None, Keys.A, this);

        hook.Register(); // registering globally that A will call a method
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0x0312)
            HandleHotkey(); // A, which was registered before, was pressed
        base.WndProc(ref m);
    }

    private void HandleHotkey()
    {
        // instead of A send Q
        KeyboardManager.PressKey(Keys.Q);
    }
}

And here the class to manage Keyboard press and release events.

public class KeyboardManager
{
    public const int INPUT_KEYBOARD = 1;
    public const int KEYEVENTF_KEYUP = 0x0002;

    public struct KEYDBINPUT
    {
        public Int16 wVk;
        public Int16 wScan;
        public Int32 dwFlags;
        public Int32 time;
        public Int32 dwExtraInfo;
        public Int32 __filler1;
        public Int32 __filler2;
    }

    public struct INPUT
    {
        public Int32 type;
        public KEYDBINPUT ki;
    }

    [DllImport("user32")]
    public static extern int SendInput(int cInputs, ref INPUT pInputs, int cbSize);

    public static void HoldKey(Keys vk)
    {
        INPUT input = new INPUT();
        input.type = INPUT_KEYBOARD;
        input.ki.dwFlags = 0;
        input.ki.wVk = (Int16)vk;
        SendInput(1, ref input, Marshal.SizeOf(input));
    }

    public static void ReleaseKey(Keys vk)
    {
        INPUT input = new INPUT();
        input.type = INPUT_KEYBOARD;
        input.ki.dwFlags = KEYEVENTF_KEYUP;
        input.ki.wVk = (Int16)vk;
        SendInput(1, ref input, Marshal.SizeOf(input));
    }

    public static void PressKey(Keys vk)
    {
        HoldKey(vk);
        ReleaseKey(vk);
    }
}

I've tested it on this textarea which I'm writing to, when I pressed A it was sending Q.

I'm not sure what will be the behavior on Warcraft III, maybe they have blocked to prevent some kind of bot or something...