Create a gist now

Instantly share code, notes, and snippets.

C# Keyboard listener
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
}
@Ciantic
Owner

Usage in WPF:

App.xaml:

<Application ...
    Startup="Application_Startup"
    Exit="Application_Exit">
    ...

App.xaml.cs:

// ...
public partial class App : Application
{
    KeyboardListener KListener = new KeyboardListener();

    private void Application_Startup(object sender, StartupEventArgs e)
    {
        KListener.KeyDown += new RawKeyEventHandler(KListener_KeyDown);
    }

    void KListener_KeyDown(object sender, RawKeyEventArgs args)
    {
        Console.WriteLine(args.Key.ToString());
        Console.WriteLine(args.ToString()); // Prints the text of pressed button, takes in account big and small letters. E.g. "Shift+a" => "A"
    }

    private void Application_Exit(object sender, ExitEventArgs e)
    {
        KListener.Dispose();
    }
}
// ...
@DominicTobias

much appreciated worked first time thanks!

@bjarkeck

KeyUp event is not working for me :(

@Rewopp

Thanks alot! The best and cleanest Keyboard listener i've came across!!
Perfect for my card reader project, excelent dead keys handling, no more double accents for me! :)

@BrainInBlack

We're using this code for our upcoming project: https://github.com/beStrangeGames/relink

If desired, we can add you to the credits, just drop me a note ;)

@ktamero

Is there any way to ignore/block keys in certain circumstances with this code?

@Urutar

The dead key handling is really neat, although there is a small quirk (in lines 398 - 405):

Writing uppercase characters with accents is not possible since the press of Shift sets [lastVKCode = 0], thus preventing to react with a proper character after a dead key
-> a check for [!string.IsNullOrEmpty(ret)] rectifies that
-> lastIsDead should also be set to false in that case, since the last key was Shift and the dead key was already handled

if (lastVKCode != 0 && lastIsDead)
{
    System.Text.StringBuilder sbTemp = new System.Text.StringBuilder(5);
    DLL_Import.ToUnicodeEx(lastVKCode, lastScanCode, lastKeyState, sbTemp, sbTemp.Capacity, (uint)0, HKL);

    if (!string.IsNullOrEmpty(ret))
    {
        lastVKCode = 0;
        lastIsDead = false;
    }
    return ret;
}

I noticed yet another issue:
While the user sees all text absolutely correct, the call to ToUnicodeEx(...) does return a wrong character, specifically after the user used the shift key to write an uppercase character.
The shift key seems to lag one character behind after it was used, aka if I write an uppercase 'A', the next character returned is also an uppercase 'A', although it shouldn't.

@hrzafer

Nice implementation. Thanks. I have a question. When a sequence of keys are pressed, is there a way to get the resulting string. For example, when users types 'a', 'b', 'c', 'backspace' and 'd', does this class has any method which returns "abd"? Thanks

@naumanumer

Thanks a lot and i have a question that how can we check that two buttons are pressed like ctrl + a etc..

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment