C# Keyboard listener

keyboardlistener.cs

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using System.Windows.Input;
using System.Windows.Threading;
using System.Collections.Generic;

namespace Ownskit.Utils
{
    /// <summary>
    /// Listens keyboard globally.
    /// 
    /// <remarks>Uses WH_KEYBOARD_LL.</remarks>
    /// </summary>
    public class KeyboardListener : IDisposable
    {
        /// <summary>
        /// Creates global keyboard listener.
        /// </summary>
        public KeyboardListener()
        {
            // Dispatcher thread handling the KeyDown/KeyUp events.
            this.dispatcher = Dispatcher.CurrentDispatcher;
            
            // We have to store the LowLevelKeyboardProc, so that it is not garbage collected runtime
            hookedLowLevelKeyboardProc = (InterceptKeys.LowLevelKeyboardProc)LowLevelKeyboardProc;

            // Set the hook
            hookId = InterceptKeys.SetHook(hookedLowLevelKeyboardProc);

            // Assign the asynchronous callback event
            hookedKeyboardCallbackAsync = new KeyboardCallbackAsync(KeyboardListener_KeyboardCallbackAsync);
        }

        private Dispatcher dispatcher;

        /// <summary>
        /// Destroys global keyboard listener.
        /// </summary>
        ~KeyboardListener()
        {
            Dispose();
        }

        /// <summary>
        /// Fired when any of the keys is pressed down.
        /// </summary>
        public event RawKeyEventHandler KeyDown;

        /// <summary>
        /// Fired when any of the keys is released.
        /// </summary>
        public event RawKeyEventHandler KeyUp;

        #region Inner workings

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

        /// <summary>
        /// Asynchronous callback hook.
        /// </summary>
        /// <param name="character">Character</param>
        /// <param name="keyEvent">Keyboard event</param>
        /// <param name="vkCode">VKCode</param>
        private delegate void KeyboardCallbackAsync(InterceptKeys.KeyEvent keyEvent, int vkCode, string character);

        /// <summary>
        /// Actual callback hook.
        /// 
        /// <remarks>Calls asynchronously the asyncCallback.</remarks>
        /// </summary>
        /// <param name="nCode"></param>
        /// <param name="wParam"></param>
        /// <param name="lParam"></param>
        /// <returns></returns>
        [MethodImpl(MethodImplOptions.NoInlining)]
        private IntPtr LowLevelKeyboardProc(int nCode, UIntPtr wParam, IntPtr lParam)
        {
            string chars = "";

            if (nCode >= 0)
                if (wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_KEYDOWN ||
                    wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_KEYUP ||
                    wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_SYSKEYDOWN ||
                    wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_SYSKEYUP)
                {
                    // Captures the character(s) pressed only on WM_KEYDOWN
                    chars = InterceptKeys.VKCodeToString((uint)Marshal.ReadInt32(lParam), 
                        (wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_KEYDOWN ||
                        wParam.ToUInt32() == (int)InterceptKeys.KeyEvent.WM_SYSKEYDOWN));

                    hookedKeyboardCallbackAsync.BeginInvoke((InterceptKeys.KeyEvent)wParam.ToUInt32(), Marshal.ReadInt32(lParam), chars, null, null);
                }
            
            return InterceptKeys.CallNextHookEx(hookId, nCode, wParam, lParam);
        }

        /// <summary>
        /// Event to be invoked asynchronously (BeginInvoke) each time key is pressed.
        /// </summary>
        private KeyboardCallbackAsync hookedKeyboardCallbackAsync;

        /// <summary>
        /// Contains the hooked callback in runtime.
        /// </summary>
        private InterceptKeys.LowLevelKeyboardProc hookedLowLevelKeyboardProc;

        /// <summary>
        /// HookCallbackAsync procedure that calls accordingly the KeyDown or KeyUp events.
        /// </summary>
        /// <param name="keyEvent">Keyboard event</param>
        /// <param name="vkCode">VKCode</param>
        /// <param name="character">Character as string.</param>
        void KeyboardListener_KeyboardCallbackAsync(InterceptKeys.KeyEvent keyEvent, int vkCode, string character)
        {
            switch (keyEvent)
            {
                // KeyDown events
                case InterceptKeys.KeyEvent.WM_KEYDOWN:
                    if (KeyDown != null)
                        dispatcher.BeginInvoke(new RawKeyEventHandler(KeyDown), this, new RawKeyEventArgs(vkCode, false, character));
                    break;
                case InterceptKeys.KeyEvent.WM_SYSKEYDOWN:
                    if (KeyDown != null)
                        dispatcher.BeginInvoke(new RawKeyEventHandler(KeyDown), this, new RawKeyEventArgs(vkCode, true, character));
                    break;

                // KeyUp events
                case InterceptKeys.KeyEvent.WM_KEYUP:
                    if (KeyUp != null)
                        dispatcher.BeginInvoke(new RawKeyEventHandler(KeyUp), this, new RawKeyEventArgs(vkCode, false, character));
                    break;
                case InterceptKeys.KeyEvent.WM_SYSKEYUP:
                    if (KeyUp != null)
                        dispatcher.BeginInvoke(new RawKeyEventHandler(KeyUp), this, new RawKeyEventArgs(vkCode, true, character));
                    break;

                default:
                    break;
            }
        }

        #endregion

        #region IDisposable Members

        /// <summary>
        /// Disposes the hook.
        /// <remarks>This call is required as it calls the UnhookWindowsHookEx.</remarks>
        /// </summary>
        public void Dispose()
        {
            InterceptKeys.UnhookWindowsHookEx(hookId);
        }

        #endregion
    }

    /// <summary>
    /// Raw KeyEvent arguments.
    /// </summary>
    public class RawKeyEventArgs : EventArgs
    {
        /// <summary>
        /// VKCode of the key.
        /// </summary>
        public int VKCode;

        /// <summary>
        /// WPF Key of the key.
        /// </summary>
        public Key Key;

        /// <summary>
        /// Is the hitted key system key.
        /// </summary>
        public bool IsSysKey;

        /// <summary>
        /// Convert to string.
        /// </summary>
        /// <returns>Returns string representation of this key, if not possible empty string is returned.</returns>
        public override string ToString()
        {
            return Character;
        }

        /// <summary>
        /// Unicode character of key pressed.
        /// </summary>
        public string Character;

        /// <summary>
        /// Create raw keyevent arguments.
        /// </summary>
        /// <param name="VKCode"></param>
        /// <param name="isSysKey"></param>
        /// <param name="Character">Character</param>
        public RawKeyEventArgs(int VKCode, bool isSysKey, string Character)
        {
            this.VKCode = VKCode;
            this.IsSysKey = isSysKey;
            this.Character = Character;
            this.Key = System.Windows.Input.KeyInterop.KeyFromVirtualKey(VKCode);
        }

    }

    /// <summary>
    /// Raw keyevent handler.
    /// </summary>
    /// <param name="sender">sender</param>
    /// <param name="args">raw keyevent arguments</param>
    public delegate void RawKeyEventHandler(object sender, RawKeyEventArgs args);

    #region WINAPI Helper class
    /// <summary>
    /// Winapi Key interception helper class.
    /// </summary>
    internal static class InterceptKeys
    {
        public delegate IntPtr LowLevelKeyboardProc(int nCode, UIntPtr wParam, IntPtr lParam);
        public static int WH_KEYBOARD_LL = 13;

        /// <summary>
        /// Key event
        /// </summary>
        public enum KeyEvent : int {    
            /// <summary>
            /// Key down
            /// </summary>
            WM_KEYDOWN = 256,

            /// <summary>
            /// Key up
            /// </summary>
            WM_KEYUP = 257,

            /// <summary>
            /// System key up
            /// </summary>
            WM_SYSKEYUP = 261,

            /// <summary>
            /// System key down
            /// </summary>
            WM_SYSKEYDOWN = 260
        }

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

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

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

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

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

        #region Convert VKCode to string
        // Note: Sometimes single VKCode represents multiple chars, thus string. 
        // E.g. typing "^1" (notice that when pressing 1 the both characters appear, 
        // because of this behavior, "^" is called dead key)

        [DllImport("user32.dll")]
        private static extern int ToUnicodeEx(uint wVirtKey, uint wScanCode, byte[] lpKeyState, [Out, MarshalAs(UnmanagedType.LPWStr)] System.Text.StringBuilder pwszBuff, int cchBuff, uint wFlags, IntPtr dwhkl);

        [DllImport("user32.dll")]
        private static extern bool GetKeyboardState(byte[] lpKeyState);

        [DllImport("user32.dll")]
        private static extern uint MapVirtualKeyEx(uint uCode, uint uMapType, IntPtr dwhkl);

        [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
        private static extern IntPtr GetKeyboardLayout(uint dwLayout);

        [DllImport("User32.dll")]
        private static extern IntPtr GetForegroundWindow();

        [DllImport("User32.dll")]
        private static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

        [DllImport("user32.dll")]
        private static extern bool AttachThreadInput(uint idAttach, uint idAttachTo, bool fAttach);

        [DllImport("kernel32.dll")]
        private static extern uint GetCurrentThreadId();

        private static uint lastVKCode = 0;
        private static uint lastScanCode = 0;
        private static byte[] lastKeyState = new byte[255];
        private static bool lastIsDead = false;

        /// <summary>
        /// Convert VKCode to Unicode.
        /// <remarks>isKeyDown is required for because of keyboard state inconsistencies!</remarks>
        /// </summary>
        /// <param name="VKCode">VKCode</param>
        /// <param name="isKeyDown">Is the key down event?</param>
        /// <returns>String representing single unicode character.</returns>
        public static string VKCodeToString(uint VKCode, bool isKeyDown)
        {
            // ToUnicodeEx needs StringBuilder, it populates that during execution.
            System.Text.StringBuilder sbString = new System.Text.StringBuilder(5);

            byte[] bKeyState = new byte[255];
            bool bKeyStateStatus;
            bool isDead = false;

            // Gets the current windows window handle, threadID, processID
            IntPtr currentHWnd = GetForegroundWindow();
            uint currentProcessID;
            uint currentWindowThreadID = GetWindowThreadProcessId(currentHWnd, out currentProcessID);

            // This programs Thread ID
            uint thisProgramThreadId = GetCurrentThreadId();

            // Attach to active thread so we can get that keyboard state
            if (AttachThreadInput(thisProgramThreadId, currentWindowThreadID , true))
            {
                // Current state of the modifiers in keyboard
                bKeyStateStatus = GetKeyboardState(bKeyState);

                // Detach
                AttachThreadInput(thisProgramThreadId, currentWindowThreadID, false);
            }
            else
            {
                // Could not attach, perhaps it is this process?
                bKeyStateStatus = GetKeyboardState(bKeyState);
            }

            // On failure we return empty string.
            if (!bKeyStateStatus)
                return "";

            // Gets the layout of keyboard
            IntPtr HKL = GetKeyboardLayout(currentWindowThreadID);

            // Maps the virtual keycode
            uint lScanCode = MapVirtualKeyEx(VKCode, 0, HKL);

            // Keyboard state goes inconsistent if this is not in place. In other words, we need to call above commands in UP events also.
            if (!isKeyDown)
                return "";

            // Converts the VKCode to unicode
            int relevantKeyCountInBuffer = ToUnicodeEx(VKCode, lScanCode, bKeyState, sbString, sbString.Capacity, (uint)0, HKL);

            string ret = "";

            switch (relevantKeyCountInBuffer)
            {
                // Dead keys (^,`...)
                case -1:
                    isDead = true;

                    // We must clear the buffer because ToUnicodeEx messed it up, see below.
                    ClearKeyboardBuffer(VKCode, lScanCode, HKL);
                    break;

                case 0:
                    break;

                // Single character in buffer
                case 1:
                    ret = sbString[0].ToString();
                    break;

                // Two or more (only two of them is relevant)
                case 2:
                default:
                    ret = sbString.ToString().Substring(0, 2);
                    break;
            }

            // We inject the last dead key back, since ToUnicodeEx removed it.
            // More about this peculiar behavior see e.g: 
            //   http://www.experts-exchange.com/Programming/System/Windows__Programming/Q_23453780.html
            //   http://blogs.msdn.com/michkap/archive/2005/01/19/355870.aspx
            //   http://blogs.msdn.com/michkap/archive/2007/10/27/5717859.aspx
            if (lastVKCode != 0 && lastIsDead)
            {
                System.Text.StringBuilder sbTemp = new System.Text.StringBuilder(5);
                ToUnicodeEx(lastVKCode, lastScanCode, lastKeyState, sbTemp, sbTemp.Capacity, (uint)0, HKL);
                lastVKCode = 0;

                return ret;
            }
        
            // Save these
            lastScanCode = lScanCode;
            lastVKCode = VKCode;
            lastIsDead = isDead;
            lastKeyState = (byte[])bKeyState.Clone();

            return ret;
        }

        private static void ClearKeyboardBuffer(uint vk, uint sc, IntPtr hkl)
        {
            System.Text.StringBuilder sb = new System.Text.StringBuilder(10);
            
            int rc;
            do {
                byte[] lpKeyStateNull = new Byte[255];
                rc = ToUnicodeEx(vk, sc, lpKeyStateNull, sb, sb.Capacity, 0, hkl);
            } while(rc < 0);
        }
        #endregion
    }
    #endregion
}