C# global keyboard hook, that opens a form from a

Question

This question already has an answer here:

• Capture a keyboard keypress in the background 2 answers

So I have a C# Console Application with a Form, which I want to open using hotkeys. Let's say for example Ctrl + < opens the form. So I got the code to handle a globalkeylistener now, but it looks like I failed by implementing it. It made a while loop to prevent it from closing the program and I tryed to get an input from the user with the kbh_OnKeyPressed method.

I tryed to implement it this way:

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Globalkey
{
    static class Program
    {
        [DllImport("user32.dll")]
        private static extern bool RegisterHotkey(int id, uint fsModifiers, uint vk);

        private static bool lctrlKeyPressed;
        private static bool f1KeyPressed;


        [STAThread]
        static void Main()
        {

            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            LowLevelKeyboardHook kbh = new LowLevelKeyboardHook();
            kbh.OnKeyPressed += kbh_OnKeyPressed;
            kbh.OnKeyUnpressed += kbh_OnKeyUnpressed;
            kbh.HookKeyboard();

            while(true) { }

        }

        private static void kbh_OnKeyUnpressed(object sender, Keys e)
        {
            if (e == Keys.LControlKey)
            {
                lctrlKeyPressed = false;
                Console.WriteLine("CTRL unpressed");
            }
            else if (e == Keys.F1)
            {
                f1KeyPressed = false;
                Console.WriteLine("F1 unpressed");
            }
        }

        private static void kbh_OnKeyPressed(object sender, Keys e)
        {
            if (e == Keys.LControlKey)
            {
                lctrlKeyPressed = true;
                Console.WriteLine("CTRL pressed");
            }
            else if (e == Keys.F1)
            {
                f1KeyPressed = true;
                Console.WriteLine("F1 pressed");
            }
            CheckKeyCombo();
        }

        static void CheckKeyCombo()
        {
            if (lctrlKeyPressed && f1KeyPressed)
            {
                Application.Run(new Form1());
            }
        }
    }
}

Answer 1

What you need is a Lowlevel Keyboard Hook.

This could look somewhat like this:

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public class LowLevelKeyboardHook
{
    private const int WH_KEYBOARD_LL = 13;
    private const int WM_KEYDOWN = 0x0100;
    private const int WM_SYSKEYDOWN = 0x0104;
    private const int WM_KEYUP = 0x101;
    private const int WM_SYSKEYUP = 0x105;

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr GetModuleHandle(string lpModuleName);

    public delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

    public event EventHandler<Keys> OnKeyPressed;
    public event EventHandler<Keys> OnKeyUnpressed;

    private LowLevelKeyboardProc _proc;
    private IntPtr _hookID = IntPtr.Zero;

    public LowLevelKeyboardHook()
    {
        _proc = HookCallback;
    }

    public void HookKeyboard()
    {
        _hookID = SetHook(_proc);
    }

    public void UnHookKeyboard()
    {
        UnhookWindowsHookEx(_hookID);
    }

    private IntPtr SetHook(LowLevelKeyboardProc proc)
    {
        using (Process curProcess = Process.GetCurrentProcess())
        using (ProcessModule curModule = curProcess.MainModule)
        {
            return SetWindowsHookEx(WH_KEYBOARD_LL, proc, GetModuleHandle(curModule.ModuleName), 0);
        }
    }

    private IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
    {
        if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN || wParam == (IntPtr)WM_SYSKEYDOWN)
        {
            int vkCode = Marshal.ReadInt32(lParam);

            OnKeyPressed.Invoke(this, ((Keys)vkCode));
        }
        else if(nCode >= 0 && wParam == (IntPtr)WM_KEYUP ||wParam == (IntPtr)WM_SYSKEYUP)
        {
            int vkCode = Marshal.ReadInt32(lParam);

            OnKeyUnpressed.Invoke(this, ((Keys)vkCode));
        }

        return CallNextHookEx(_hookID, nCode, wParam, lParam);            
    }
}

To implement it, you could use something like this:

kbh = new LowLevelKeyboardHook();
kbh.OnKeyPressed += kbh_OnKeyPressed;
kbh.OnKeyUnpressed += kbh_OnKeyUnpressed;
kbh.HookKeyboard();

The event could be handled like that:

bool lctrlKeyPressed;
bool f1KeyPressed;

void kbh_OnKeyPressed(object sender, Keys e)
{
    if (e == Keys.LControlKey)
    {
        lctrlKeyPressed = true;
    }
    else if (e == Keys.F1)
    {
        f1KeyPressed= true;
    }
    CheckKeyCombo();
}

void kbh_OnKeyUnPressed(object sender, Keys e)
{
    if (e == Keys.LControlKey)
    {
        lctrlKeyPressed = false;
    }
    else if (e == Keys.F1)
    {
        f1KeyPressed= false;
    }
}

void CheckKeyCombo()
{
    if (lctrlKeyPressed && f1KeyPressed)
    {
        //Open Form
    }
}

For actual understanding, i would recommend you to have a read on P/Invoke. That is making use of the unmanaged APIs that windows provides.

For a full list of P/Invoke possibilites, pinvoke.net is a great source.

For better understanding in general, The official MSDN Website is a good source, too.

EDIT:

It seems like you're actually using a Console Application, not a WinForm one. In that case, you have to run the program a bit differently:

[STAThread]
static void Main()
{

    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    LowLevelKeyboardHook kbh = new LowLevelKeyboardHook();
    kbh.OnKeyPressed += kbh_OnKeyPressed;
    kbh.OnKeyUnpressed += kbh_OnKeyUnpressed;
    kbh.HookKeyboard();

    Application.Run();

    kbh.UnHookKeyboard();

}

The Run() method of the Application Class starts a standard loop for your application. This is necessary for the Hook to work, because a mere Console Application without this loop is, as far as I know, not capable of triggering those global key events.

Using this implementation, pressing and releasing the defined keys gives the following output:

Note: I obviously replaced

Application.Run(new Form1());

in the CheckKeyCombo() method with

Console.WriteLine("KeyCombo pressed");