KeyboardHook.cs

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

namespace Echoes
{
    /// <summary>
    /// Class for intercepting low level keyboard hooks
    /// </summary>
    public class KeyboardHook
    {

        private const int VK_SHIFT = 0x10;
        private const int VK_CONTROL = 0x11;
        private const int VK_MENU = 0x12;
        private const int VK_CAPITAL = 0x14;

        public List<Keys> suppressedKeys = new List<Keys>();

        /// <summary>
        /// Internal callback processing function
        /// </summary>
        private delegate IntPtr KeyboardHookHandler(int nCode, IntPtr wParam, IntPtr lParam);
        private KeyboardHookHandler hookHandler;

        /// <summary>
        /// Function that will be called when defined events occur
        /// </summary>
        /// <param name="key">VKeys</param>
        public delegate void KeyboardHookCallback(KeyEventArgs e);

        #region Events
        public event KeyboardHookCallback KeyDown;
        public event KeyboardHookCallback KeyUp;
        #endregion

        /// <summary>
        /// Hook ID
        /// </summary>
        private IntPtr hookID = IntPtr.Zero;

        /// <summary>
        /// Install low level keyboard hook
        /// </summary>
        public void Install()
        {
            hookHandler = HookFunc;
            hookID = SetHook(hookHandler);
        }

        /// <summary>
        /// Remove low level keyboard hook
        /// </summary>
        public void Uninstall()
        {
            UnhookWindowsHookEx(hookID);
        }

        /// <summary>
        /// Registers hook with Windows API
        /// </summary>
        /// <param name="proc">Callback function</param>
        /// <returns>Hook ID</returns>
        private IntPtr SetHook(KeyboardHookHandler proc)
        {
            using (ProcessModule module = Process.GetCurrentProcess().MainModule)
                return SetWindowsHookEx(13, proc, GetModuleHandle(module.ModuleName), 0);
        }

        /// <summary>
        /// Default hook call, which analyses pressed keys
        /// </summary>
        private IntPtr HookFunc(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                int iwParam = wParam.ToInt32();
                Keys key = (Keys)Marshal.ReadInt32(lParam);
                key = AddModifiers(key);

                if ((iwParam == WM_KEYDOWN || iwParam == WM_SYSKEYDOWN))
                    if (KeyDown != null)
                        KeyDown(new KeyEventArgs(key));
                if ((iwParam == WM_KEYUP || iwParam == WM_SYSKEYUP))
                    if (KeyUp != null)
                        KeyUp(new KeyEventArgs(key));
                if (suppressedKeys.Contains(key)) return (System.IntPtr)1;
            }
            return CallNextHookEx(hookID, nCode, wParam, lParam);
        }

        /// <summary>
        /// Checks whether Alt, Shift, Control or CapsLock
        /// is pressed at the same time as the hooked key.
        /// Modifies the keyCode to include the pressed keys.
        /// </summary>
        private Keys AddModifiers(Keys key)
        {
            //CapsLock
            if ((GetKeyState(VK_CAPITAL) & 0x0001) != 0) key = key | Keys.CapsLock;

            //Shift
            if ((GetKeyState(VK_SHIFT) & 0x8000) != 0) key = key | Keys.Shift;

            //Ctrl
            if ((GetKeyState(VK_CONTROL) & 0x8000) != 0) key = key | Keys.Control;

            //Alt
            if ((GetKeyState(VK_MENU) & 0x8000) != 0) key = key | Keys.Alt;

            return key;
        }

        /// <summary>
        /// Destructor. Unhook current hook
        /// </summary>
        ~KeyboardHook()
        {
            Uninstall();
        }

        /// <summary>
        /// Low-Level function declarations
        /// </summary>
        #region WinAPI
        private const int WM_KEYDOWN = 0x100;
        private const int WM_SYSKEYDOWN = 0x104;
        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, KeyboardHookHandler 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("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true, CallingConvention = CallingConvention.Winapi)]
        public static extern short GetKeyState(int keyCode);

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