C# Hook Global Keyboard Events - .net 4.0

Question

As part of a media player application I'm working on, I want to hook global key presses for media control keys (play, skip forward, skip back, etc).

I've been searching for about 2 hours now trying to find a solution - but I couldn't find one that worked. I found several Stack Overflow answers about the same thing, but none of them worked.

I tried the MouseKeyHook NuGet package, but it would never fire the event. I tried the FMUtils.KeyboardHook package too, but the same thing happened, except it printed in the console that it shut down the hook right after starting it - and I have no idea why, even after looking at the source code.

I tried to get this codeproject project http://www.codeproject.com/Articles/18638/Using-Window-Messages-to-Implement-Global-System-H but I couldn't even run the demo, both the demos just threw weird errors that I couldn't trace.

My question is, what is a known-to-work way of capturing keyboard presses in .NET 4.0 that I can use to capture keyboard presses when my WinForms application isn't focused?

Answer 1

Here is the code I have been using for several projects for the last X years. Should work with no issues (for any .NET version on Windows).

public class KeyboardHook : IDisposable
{
    bool Global = false;

    public delegate void LocalKeyEventHandler(Keys key, bool Shift, bool Ctrl, bool Alt);
    public event LocalKeyEventHandler KeyDown;
    public event LocalKeyEventHandler KeyUp;

    public delegate int CallbackDelegate(int Code, int W, int L);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public struct KBDLLHookStruct
    {
        public Int32 vkCode;
        public Int32 scanCode;
        public Int32 flags;
        public Int32 time;
        public Int32 dwExtraInfo;
    }

    [DllImport("user32", CallingConvention = CallingConvention.StdCall)]
    private static extern int SetWindowsHookEx(HookType idHook, CallbackDelegate lpfn, int hInstance, int threadId);

    [DllImport("user32", CallingConvention = CallingConvention.StdCall)]
    private static extern bool UnhookWindowsHookEx(int idHook);

    [DllImport("user32", CallingConvention = CallingConvention.StdCall)]
    private static extern int CallNextHookEx(int idHook, int nCode, int wParam, int lParam);

    [DllImport("kernel32.dll", CallingConvention = CallingConvention.StdCall)]
    private static extern int GetCurrentThreadId();

    public enum HookType : int
    {
        WH_JOURNALRECORD = 0,
        WH_JOURNALPLAYBACK = 1,
        WH_KEYBOARD = 2,
        WH_GETMESSAGE = 3,
        WH_CALLWNDPROC = 4,
        WH_CBT = 5,
        WH_SYSMSGFILTER = 6,
        WH_MOUSE = 7,
        WH_HARDWARE = 8,
        WH_DEBUG = 9,
        WH_SHELL = 10,
        WH_FOREGROUNDIDLE = 11,
        WH_CALLWNDPROCRET = 12,
        WH_KEYBOARD_LL = 13,
        WH_MOUSE_LL = 14
    }

    private int HookID = 0;
    CallbackDelegate TheHookCB = null;

    //Start hook
    public KeyboardHook(bool Global)
    {
        this.Global = Global;
        TheHookCB = new CallbackDelegate(KeybHookProc);
        if (Global)
        {
            HookID = SetWindowsHookEx(HookType.WH_KEYBOARD_LL, TheHookCB,
                0, //0 for local hook. eller hwnd til user32 for global
                0); //0 for global hook. eller thread for hooken
        }
        else
        {
            HookID = SetWindowsHookEx(HookType.WH_KEYBOARD, TheHookCB,
                0, //0 for local hook. or hwnd to user32 for global
                GetCurrentThreadId()); //0 for global hook. or thread for the hook
        }
    }

    bool IsFinalized = false;
    ~KeyboardHook()
    {
        if (!IsFinalized)
        {
            UnhookWindowsHookEx(HookID);
            IsFinalized = true;
        }
    }
    public void Dispose()
    {
        if (!IsFinalized)
        {
            UnhookWindowsHookEx(HookID);
            IsFinalized = true;
        }
    }

    //The listener that will trigger events
    private int KeybHookProc(int Code, int W, int L)
    {
        KBDLLHookStruct LS = new KBDLLHookStruct();
        if (Code < 0)
        {
            return CallNextHookEx(HookID, Code, W, L);
        }
        try
        {
            if (!Global)
            {
                if (Code == 3)
                {
                    IntPtr ptr = IntPtr.Zero;

                    int keydownup = L >> 30;
                    if (keydownup == 0)
                    {
                        if (KeyDown != null) KeyDown((Keys)W, GetShiftPressed(), GetCtrlPressed(), GetAltPressed());
                    }
                    if (keydownup == -1)
                    {
                        if (KeyUp != null) KeyUp((Keys)W, GetShiftPressed(), GetCtrlPressed(), GetAltPressed());
                    }
                    //System.Diagnostics.Debug.WriteLine("Down: " + (Keys)W);
                }
            }
            else
            {
                KeyEvents kEvent = (KeyEvents)W;

                Int32 vkCode = Marshal.ReadInt32((IntPtr)L); //Leser vkCode som er de første 32 bits hvor L peker.

                if (kEvent != KeyEvents.KeyDown && kEvent != KeyEvents.KeyUp && kEvent != KeyEvents.SKeyDown && kEvent != KeyEvents.SKeyUp)
                {
                }
                if (kEvent == KeyEvents.KeyDown || kEvent == KeyEvents.SKeyDown)
                {
                    if (KeyDown != null) KeyDown((Keys)vkCode, GetShiftPressed(), GetCtrlPressed(), GetAltPressed());
                }
                if (kEvent == KeyEvents.KeyUp || kEvent == KeyEvents.SKeyUp)
                {
                    if (KeyUp != null) KeyUp((Keys)vkCode, GetShiftPressed(), GetCtrlPressed(), GetAltPressed());
                }
            }
        }
        catch (Exception)
        {
            //Ignore all errors...
        }

        return CallNextHookEx(HookID, Code, W, L);

    }

    public enum KeyEvents
    {
        KeyDown = 0x0100,
        KeyUp = 0x0101,
        SKeyDown = 0x0104,
        SKeyUp = 0x0105
    }

    [DllImport("user32.dll")]
    static public extern short GetKeyState(System.Windows.Forms.Keys nVirtKey);

    public static bool GetCapslock()
    {   
        return Convert.ToBoolean(GetKeyState(System.Windows.Forms.Keys.CapsLock)) & true;
    }
    public static bool GetNumlock()
    { 
        return Convert.ToBoolean(GetKeyState(System.Windows.Forms.Keys.NumLock)) & true;
    }
    public static bool GetScrollLock()
    { 
        return Convert.ToBoolean(GetKeyState(System.Windows.Forms.Keys.Scroll)) & true;
    }
    public static bool GetShiftPressed()
    { 
        int state = GetKeyState(System.Windows.Forms.Keys.ShiftKey);
        if (state > 1 || state < -1) return true;
        return false;
    }
    public static bool GetCtrlPressed()
    { 
        int state = GetKeyState(System.Windows.Forms.Keys.ControlKey);
        if (state > 1 || state < -1) return true;
        return false;
    }
    public static bool GetAltPressed()
    { 
        int state = GetKeyState(System.Windows.Forms.Keys.Menu);
        if (state > 1 || state < -1) return true;
        return false;
    }
}

Test app:

static class Program
{
    [STAThread]
    static void Main()
    {
        var kh = new KeyboardHook(true);
        kh.KeyDown += Kh_KeyDown;
        Application.Run();
    }

    private static void Kh_KeyDown(Keys key, bool Shift, bool Ctrl, bool Alt)
    {
        Debug.WriteLine("The Key: " + key);
    }
}

It could do with some code cleanup, but I have not bothered as it works.