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How to read keyboard input while form is in the background c#

I need to be able to read keyboard input while my form is in the background (not necessarily hidden). There are simmilar questions here but I need to be albe to determine witch key is pressed and I need to get its value as "Key" not int (stuff like 0x00357 and I have no idea what that is). Specifically I need to check if key determined by user is currently pressed. How can I do that?

A few years later than you asked, but this is what I used when creating an app that would listen to key presses, and anything in a predefined list would be mirrored to other background processes to enable multi-boxing in a game.
There is a great keyboard listener at Ciantic's Github, and in case the link is invalid then here's the code -
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
}
From the author, this is the usage -
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();
}
}
If you also need to listen for KeyUp events then you can create a listener for that as well. The RawKeyEventArgs that is generated contains the key name, character pressed, and virtual key code. You can use any of these to compare with your existing list that you're wanting to respond to, and react accordingly. If you need to verify what key presses will look like then you can display a message box of anything entered and build yourself a list from there.
I hope this helps!

Resolving "callback was made on a garbage collected delegate" using unmanaged code [duplicate]

I have been using this key hook script i found but I continue to get an error after a few seconds of using it in my program. The error says.. A call has been made on a garbage collected delegate 'keylogger!Utilities.globalKeyboardHook+keyboardHookProc::Invoke'.
How can I fix this?
namespace Utilities
{
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class globalKeyboardHook
{
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
public struct keyboardHookStruct
{
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x100;
const int WM_KEYUP = 0x101;
const int WM_SYSKEYDOWN = 0x104;
const int WM_SYSKEYUP = 0x105;
#endregion
#region Instance Variables
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
IntPtr hhook = IntPtr.Zero;
#endregion
#region Events
/// <summary>
/// Occurs when one of the hooked keys is pressed
/// </summary>
public event KeyEventHandler KeyDown;
/// <summary>
/// Occurs when one of the hooked keys is released
/// </summary>
public event KeyEventHandler KeyUp;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public globalKeyboardHook()
{
hook();
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~globalKeyboardHook()
{
unhook();
}
#endregion
#region Public Methods
/// <summary>
/// Installs the global hook
/// </summary>
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void unhook()
{
UnhookWindowsHookEx(hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
{
if (code >= 0)
{
Keys key = (Keys)lParam.vkCode;
if (HookedKeys.Contains(key))
{
KeyEventArgs kea = new KeyEventArgs(key);
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
{
KeyDown(this, kea);
}
else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
{
KeyUp(this, kea);
}
if (kea.Handled)
return 1;
}
}
return CallNextHookEx(hhook, code, wParam, ref lParam);
}
#endregion
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
}
globalKeyboardHook class :
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.IO;
namespace Utilities
{
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class globalKeyboardHook : IDisposable
{
private bool _disposed;
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
public struct keyboardHookStruct
{
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x100;
const int WM_KEYUP = 0x101;
const int WM_SYSKEYDOWN = 0x104;
const int WM_SYSKEYUP = 0x105;
#endregion
#region Instance Variables
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
IntPtr hhook = IntPtr.Zero;
#endregion
#region Events
/// <summary>
/// Occurs when one of the hooked keys is pressed
/// </summary>
public event KeyEventHandler KeyDown;
/// <summary>
/// Occurs when one of the hooked keys is released
/// </summary>
public event KeyEventHandler KeyUp;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public globalKeyboardHook()
{
hook();
_disposed = false;
}
public void Dispose()
{
Dispose(true);
// Use SupressFinalize in case a subclass
// of this type implements a finalizer.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
// If you need thread safety, use a lock around these
// operations, as well as in your methods that use the resource.
if (!_disposed)
{
if (disposing)
{
unhook();
}
// Indicate that the instance has been disposed.
_disposed = true;
}
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~globalKeyboardHook()
{
Dispose();
}
#endregion
#region Public Methods
/// <summary>
/// Installs the global hook
/// </summary>
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, new keyboardHookProc(hookProc), hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void unhook()
{
UnhookWindowsHookEx(hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
{
if (code >= 0)
{
Keys key = (Keys)lParam.vkCode;
if (HookedKeys.Contains(key))
{
KeyEventArgs kea = new KeyEventArgs(key);
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
{
KeyDown(this, kea);
}
else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
{
KeyUp(this, kea);
}
if (kea.Handled)
return 1;
}
}
return CallNextHookEx(hhook, code, wParam, ref lParam);
}
#endregion
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
}
I updated the code with IDisposable. I am probably horribly off on what I am supposed to do but its still not working

The problem is that:
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
is just syntactic sugar for:
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, new keyboardHookProc(hookProc), hInstance, 0);
and so the keyboardHookProc object is just local and will get disposed of since SetWindowsHookEx doesn't do anything to actually hold onto it in the managed world.
To fix this, up at the top where you define your member variables, add one more like this:
IntPtr hhook = IntPtr.Zero
private keyboardHookProc hookProcDelegate;
then change your constructor to be:
public globalKeyboardHook()
{
hookProcDelegate = hookProc;
hook();
}
and then change your hook() method to be:
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProcDelegate, hInstance, 0);
}
That way you're using a delegate that is stored as a member variable and will be alive as long as your globalKeyboardHook object is alive.

Sounds to me like you are instantiating a globalKeyboardHook then letting it get garbage collected. I'm guessing you do something like this:
public void InstallHook()
{
var hook = new globalKeyboardHook();
}
You need to keep a reference to the globalKeyboardHook() around to prevent it from being garbage collected.
globalKeyboardHook hook;
public void InstallHook()
{
hook = new globalKeyboardHook();
}

I'd like to add this, for future reference, as it may help understanding Tim's answer, and maybe debugging what's going on, if you have complex code:
callbackOnCollectedDelegate MDA
https://learn.microsoft.com/en-us/dotnet/framework/debug-trace-profile/callbackoncollecteddelegate-mda

even though with the new code I am still getting the mentioned error, as a solution I just kept an instance of the delegate at class scope, now the error does not come up anymore.
//do not forget to declare kbhproc class var
this.kbhProc = new keyboardHookProc(hookProc);
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, this.kbhProc /*new keyboardHookProc(hookProc)*/, hInstance, 0);
the above code is based on the code of the question.

C# Keyboard hook throws System.NullReferenceException

When discussing keyboard hooking, this article gets thrown around a lot.
So I tied the class that it suggested:
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;
namespace Utilities {
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class globalKeyboardHook {
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
public struct keyboardHookStruct {
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x100;
const int WM_KEYUP = 0x101;
const int WM_SYSKEYDOWN = 0x104;
const int WM_SYSKEYUP = 0x105;
#endregion
#region Instance Variables
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
IntPtr hhook = IntPtr.Zero;
#endregion
#region Events
/// <summary>
/// Occurs when one of the hooked keys is pressed
/// </summary>
public event KeyEventHandler KeyDown;
/// <summary>
/// Occurs when one of the hooked keys is released
/// </summary>
public event KeyEventHandler KeyUp;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public globalKeyboardHook() {
hook();
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~globalKeyboardHook() {
unhook();
}
#endregion
#region Public Methods
/// <summary>
/// Installs the global hook
/// </summary>
public void hook() {
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void unhook() {
UnhookWindowsHookEx(hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
public int hookProc(int code, int wParam, ref keyboardHookStruct lParam) {
if (code >= 0) {
Keys key = (Keys)lParam.vkCode;
if (HookedKeys.Contains(key)) {
KeyEventArgs kea = new KeyEventArgs(key);
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null)) {
KeyDown(this, kea) ;
} else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null)) {
KeyUp(this, kea);
}
if (kea.Handled)
return 1;
}
}
return CallNextHookEx(hhook, code, wParam, ref lParam);
}
#endregion
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
}
It works for a bit, but after using the computer for a while, it will throw a System.NullReferenceException on a random key press. Especially around key combinations.
What could be causing this and how can it be fixed?
EDIT: This is the code I am using to start the hook:
globalKeyboardHook globalKeyboardHook = new globalKeyboardHook();
private void Form1_Load(object sender, EventArgs e)
{
globalKeyboardHook.KeyDown += gkh_KeyDown;
globalKeyboardHook.KeyUp += gkh_KeyUp;
globalKeyboardHook.hook();
}
And this is the complete error I am getting:
An unhandled exception of type 'System.NullReferenceException'
occurred in System.Windows.Forms.dll
Additional information: Object reference not set to an instance of an object.

Try using a field to store the callback to avoid the delegate being collected by GC:
private static keyboardHookProc callback;
public void hook()
{
callback = new keyboardHookProc(hookProc);
var hhook = SetWindowsHookEx(1, callback, IntPtr.Zero, 0);
}

Register hot key that is already used

Background:
I want to listen to a hot key sequence (Ctrl+Alt+Left) globally, so I'm using:
[DllImport("user32.dll")]
private static extern bool RegisterHotKey(IntPtr hWnd, int id, uint fsModifiers, uint vk);
This works great with many other hot key sequences, such as Ctrl+Alt+PageUp, Ctrl+Alt+PageDown, etc... But a problem occurs with Ctrl+Alt+Left, specifically.
Problem:
On one computer, it works just fine, like any other hot key sequence, but on a different computer, where Ctrl+Alt+Arrow is used to rotate the screen, it fails to register the hot key (i.e returns zero and doesn't get callbacks to the window's handle).
MSDN says: RegisterHotKey fails if the keystrokes specified for the hot key have already been registered by another hot key.
I would like to be able to register that hot key sequence no matter what, and if needed, override it. I would certainly want the screen to remain unrotated, at least for as long as my program is running.
Changing the hotkey sequence isn't really an option, since other computers might have other hotkey sequences that may cause failure as well.
Questions:
What is the difference between Ctrl+Alt+Left as a screen-rotating hotkey and a Ctrl+S as a saving hotkey, the causes one to fail but not the other? (maybe it is because one is a global hotkey and the second is contextual?)
Is it possible to override hotkeys entirely? Is that a good idea?
Most importantly, how can I assure that my hotkey will be registered?

I've just changed my approach from hotkeys to hooks.
I'm listening to any low-level keyboard press event, and getting the modifiers' states when such even fires using winAPI. Then I have full information about currently pressed sequence.
It's very long and ugly code to do all that, but eventually it is easy to work with.
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class GlobalKeyboardHook
{
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int KeyboardHookProc(int code, int wParam, ref KeyboardHookStruct lParam);
public struct KeyboardHookStruct
{
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
private const int WH_KEYBOARD_LL = 13;
private const int WM_KEYDOWN = 0x100;
private const int WM_KEYUP = 0x101;
private const int WM_SYSKEYDOWN = 0x104;
private const int WM_SYSKEYUP = 0x105;
#endregion
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
private IntPtr _hhook = IntPtr.Zero;
/// <summary>
/// Initializes a new instance of the <see cref="GlobalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public GlobalKeyboardHook()
{
this.Hook();
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="GlobalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~GlobalKeyboardHook()
{
this.Unhook();
}
/// <summary>
/// Installs the global hook
/// </summary>
public void Hook()
{
IntPtr hInstance = LoadLibrary("User32");
this._hhook = SetWindowsHookEx(WH_KEYBOARD_LL, this.HookProc, hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void Unhook()
{
UnhookWindowsHookEx(this._hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
private int HookProc(int code, int wParam, ref KeyboardHookStruct lParam)
{
if (code >= 0)
{
var key = (Keys) lParam.vkCode;
if (this.HookedKeys.Contains(key))
{
var handler = this.KeyPressed;
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (handler != null))
{
ModifierKeys mods = 0;
if (Keyboard.IsKeyDown(Keys.Control) || Keyboard.IsKeyDown(Keys.ControlKey) ||
Keyboard.IsKeyDown(Keys.LControlKey) || Keyboard.IsKeyDown(Keys.RControlKey))
{
mods |= ModifierKeys.Control;
}
if (Keyboard.IsKeyDown(Keys.Shift) || Keyboard.IsKeyDown(Keys.ShiftKey) ||
Keyboard.IsKeyDown(Keys.LShiftKey) || Keyboard.IsKeyDown(Keys.RShiftKey))
{
mods |= ModifierKeys.Shift;
}
if (Keyboard.IsKeyDown(Keys.LWin) || Keyboard.IsKeyDown(Keys.RWin))
{
mods |= ModifierKeys.Win;
}
if (Keyboard.IsKeyDown(Keys.Alt))
{
mods |= ModifierKeys.Alt;
}
handler(this, new KeyPressedEventArgs(mods, key));
}
}
}
return CallNextHookEx(this._hhook, code, wParam, ref lParam);
}
public event EventHandler<KeyPressedEventArgs> KeyPressed;
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
private static extern IntPtr SetWindowsHookEx(int idHook, KeyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
private static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
private static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref KeyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
private static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
static class Keyboard
{
[Flags]
private enum KeyStates
{
None = 0,
Down = 1,
Toggled = 2
}
[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
private static extern short GetKeyState(int keyCode);
private static KeyStates GetKeyState(Keys key)
{
KeyStates state = KeyStates.None;
short retVal = GetKeyState((int)key);
//If the high-order bit is 1, the key is down
//otherwise, it is up.
if ((retVal & 0x8000) == 0x8000)
state |= KeyStates.Down;
//If the low-order bit is 1, the key is toggled.
if ((retVal & 1) == 1)
state |= KeyStates.Toggled;
return state;
}
public static bool IsKeyDown(Keys key)
{
return KeyStates.Down == (GetKeyState(key) & KeyStates.Down);
}
public static bool IsKeyToggled(Keys key)
{
return KeyStates.Toggled == (GetKeyState(key) & KeyStates.Toggled);
}
}
/// <summary>
/// Event Args for the event that is fired after the hot key has been pressed.
/// </summary>
class KeyPressedEventArgs : EventArgs
{
internal KeyPressedEventArgs(ModifierKeys modifier, Keys key)
{
this.Modifier = modifier;
this.Key = key;
this.Ctrl = (modifier & ModifierKeys.Control) != 0;
this.Shift = (modifier & ModifierKeys.Shift) != 0;
this.Win = (modifier & ModifierKeys.Win) != 0;
this.Alt = (modifier & ModifierKeys.Alt) != 0;
}
public ModifierKeys Modifier { get; private set; }
public Keys Key { get; private set; }
public readonly bool Ctrl;
public readonly bool Shift;
public readonly bool Win;
public readonly bool Alt;
}
/// <summary>
/// The enumeration of possible modifiers.
/// </summary>
[Flags]
public enum ModifierKeys : uint
{
Alt = 1,
Control = 2,
Shift = 4,
Win = 8
}

Call has been made on garbage collected delegate in C#?

I have been using this key hook script i found but I continue to get an error after a few seconds of using it in my program. The error says.. A call has been made on a garbage collected delegate 'keylogger!Utilities.globalKeyboardHook+keyboardHookProc::Invoke'.
How can I fix this?
namespace Utilities
{
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class globalKeyboardHook
{
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
public struct keyboardHookStruct
{
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x100;
const int WM_KEYUP = 0x101;
const int WM_SYSKEYDOWN = 0x104;
const int WM_SYSKEYUP = 0x105;
#endregion
#region Instance Variables
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
IntPtr hhook = IntPtr.Zero;
#endregion
#region Events
/// <summary>
/// Occurs when one of the hooked keys is pressed
/// </summary>
public event KeyEventHandler KeyDown;
/// <summary>
/// Occurs when one of the hooked keys is released
/// </summary>
public event KeyEventHandler KeyUp;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public globalKeyboardHook()
{
hook();
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~globalKeyboardHook()
{
unhook();
}
#endregion
#region Public Methods
/// <summary>
/// Installs the global hook
/// </summary>
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void unhook()
{
UnhookWindowsHookEx(hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
{
if (code >= 0)
{
Keys key = (Keys)lParam.vkCode;
if (HookedKeys.Contains(key))
{
KeyEventArgs kea = new KeyEventArgs(key);
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
{
KeyDown(this, kea);
}
else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
{
KeyUp(this, kea);
}
if (kea.Handled)
return 1;
}
}
return CallNextHookEx(hhook, code, wParam, ref lParam);
}
#endregion
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
}
globalKeyboardHook class :
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.IO;
namespace Utilities
{
/// <summary>
/// A class that manages a global low level keyboard hook
/// </summary>
class globalKeyboardHook : IDisposable
{
private bool _disposed;
#region Constant, Structure and Delegate Definitions
/// <summary>
/// defines the callback type for the hook
/// </summary>
public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);
public struct keyboardHookStruct
{
public int vkCode;
public int scanCode;
public int flags;
public int time;
public int dwExtraInfo;
}
const int WH_KEYBOARD_LL = 13;
const int WM_KEYDOWN = 0x100;
const int WM_KEYUP = 0x101;
const int WM_SYSKEYDOWN = 0x104;
const int WM_SYSKEYUP = 0x105;
#endregion
#region Instance Variables
/// <summary>
/// The collections of keys to watch for
/// </summary>
public List<Keys> HookedKeys = new List<Keys>();
/// <summary>
/// Handle to the hook, need this to unhook and call the next hook
/// </summary>
IntPtr hhook = IntPtr.Zero;
#endregion
#region Events
/// <summary>
/// Occurs when one of the hooked keys is pressed
/// </summary>
public event KeyEventHandler KeyDown;
/// <summary>
/// Occurs when one of the hooked keys is released
/// </summary>
public event KeyEventHandler KeyUp;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
/// </summary>
public globalKeyboardHook()
{
hook();
_disposed = false;
}
public void Dispose()
{
Dispose(true);
// Use SupressFinalize in case a subclass
// of this type implements a finalizer.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
// If you need thread safety, use a lock around these
// operations, as well as in your methods that use the resource.
if (!_disposed)
{
if (disposing)
{
unhook();
}
// Indicate that the instance has been disposed.
_disposed = true;
}
}
/// <summary>
/// Releases unmanaged resources and performs other cleanup operations before the
/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
/// </summary>
~globalKeyboardHook()
{
Dispose();
}
#endregion
#region Public Methods
/// <summary>
/// Installs the global hook
/// </summary>
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, new keyboardHookProc(hookProc), hInstance, 0);
}
/// <summary>
/// Uninstalls the global hook
/// </summary>
public void unhook()
{
UnhookWindowsHookEx(hhook);
}
/// <summary>
/// The callback for the keyboard hook
/// </summary>
/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>
/// <param name="wParam">The event type</param>
/// <param name="lParam">The keyhook event information</param>
/// <returns></returns>
public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)
{
if (code >= 0)
{
Keys key = (Keys)lParam.vkCode;
if (HookedKeys.Contains(key))
{
KeyEventArgs kea = new KeyEventArgs(key);
if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))
{
KeyDown(this, kea);
}
else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))
{
KeyUp(this, kea);
}
if (kea.Handled)
return 1;
}
}
return CallNextHookEx(hhook, code, wParam, ref lParam);
}
#endregion
#region DLL imports
/// <summary>
/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
/// </summary>
/// <param name="idHook">The id of the event you want to hook</param>
/// <param name="callback">The callback.</param>
/// <param name="hInstance">The handle you want to attach the event to, can be null</param>
/// <param name="threadId">The thread you want to attach the event to, can be null</param>
/// <returns>a handle to the desired hook</returns>
[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);
/// <summary>
/// Unhooks the windows hook.
/// </summary>
/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
/// <returns>True if successful, false otherwise</returns>
[DllImport("user32.dll")]
static extern bool UnhookWindowsHookEx(IntPtr hInstance);
/// <summary>
/// Calls the next hook.
/// </summary>
/// <param name="idHook">The hook id</param>
/// <param name="nCode">The hook code</param>
/// <param name="wParam">The wparam.</param>
/// <param name="lParam">The lparam.</param>
/// <returns></returns>
[DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);
/// <summary>
/// Loads the library.
/// </summary>
/// <param name="lpFileName">Name of the library</param>
/// <returns>A handle to the library</returns>
[DllImport("kernel32.dll")]
static extern IntPtr LoadLibrary(string lpFileName);
#endregion
}
}
I updated the code with IDisposable. I am probably horribly off on what I am supposed to do but its still not working

The problem is that:
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
is just syntactic sugar for:
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, new keyboardHookProc(hookProc), hInstance, 0);
and so the keyboardHookProc object is just local and will get disposed of since SetWindowsHookEx doesn't do anything to actually hold onto it in the managed world.
To fix this, up at the top where you define your member variables, add one more like this:
IntPtr hhook = IntPtr.Zero
private keyboardHookProc hookProcDelegate;
then change your constructor to be:
public globalKeyboardHook()
{
hookProcDelegate = hookProc;
hook();
}
and then change your hook() method to be:
public void hook()
{
IntPtr hInstance = LoadLibrary("User32");
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProcDelegate, hInstance, 0);
}
That way you're using a delegate that is stored as a member variable and will be alive as long as your globalKeyboardHook object is alive.

Sounds to me like you are instantiating a globalKeyboardHook then letting it get garbage collected. I'm guessing you do something like this:
public void InstallHook()
{
var hook = new globalKeyboardHook();
}
You need to keep a reference to the globalKeyboardHook() around to prevent it from being garbage collected.
globalKeyboardHook hook;
public void InstallHook()
{
hook = new globalKeyboardHook();
}

I'd like to add this, for future reference, as it may help understanding Tim's answer, and maybe debugging what's going on, if you have complex code:
callbackOnCollectedDelegate MDA
https://learn.microsoft.com/en-us/dotnet/framework/debug-trace-profile/callbackoncollecteddelegate-mda

even though with the new code I am still getting the mentioned error, as a solution I just kept an instance of the delegate at class scope, now the error does not come up anymore.
//do not forget to declare kbhproc class var
this.kbhProc = new keyboardHookProc(hookProc);
hhook = SetWindowsHookEx(WH_KEYBOARD_LL, this.kbhProc /*new keyboardHookProc(hookProc)*/, hInstance, 0);
the above code is based on the code of the question.