Question

It logs the keys to textbox currently so its safe.

PROBLEM
The problem is when i run this at virtual machine, or my friends laptop,
it hangs after pressing certain amount of keys(random).It runs perfectly fine in mine.

http://i34.tinypic.com/29o1im8.jpg

class GlobalKeyboardHook
{


    #region Definition of Structures, Constants and Delegates

    public delegate int KeyboardHookProc(int nCode, int wParam, ref GlobalKeyboardHookStruct lParam);

    public struct GlobalKeyboardHookStruct
    {
        public int vkCode;
        public int scanCode;
        public int flags;
        public int time;
        public int dwExtraInfo;
    }

    const int WM_KEYDOWN = 0x100;
    const int WM_KEYUP = 0x101;
    const int WM_SYSKEYDOWN = 0x104;
    const int WM_SYSKEYUP = 0x105;
    const int WH_KEYBOARD_LL = 13;

    #endregion

    #region Events

    public event KeyEventHandler KeyDown;
    public event KeyEventHandler KeyUp;

    #endregion

    #region Instance Variables

    public List<Keys> HookedKeys = new List<Keys>();
    IntPtr hookHandle = IntPtr.Zero;

    #endregion

    #region DLL Imports

    [DllImport("kernel32.dll")]
    static extern IntPtr LoadLibrary(string lpFileName);

    [DllImport("user32.dll", CharSet = CharSet.Auto,CallingConvention = CallingConvention.StdCall, SetLastError = true)]
    static extern IntPtr SetWindowsHookEx(int hookID, KeyboardHookProc callback, IntPtr hInstance, uint threadID);

    [DllImport("user32.dll", CharSet = CharSet.Auto,CallingConvention = CallingConvention.StdCall, SetLastError = true)]
    static extern bool UnhookWindowsHookEx(IntPtr hookHandle);

    [DllImport("user32.dll", CharSet = CharSet.Auto,CallingConvention = CallingConvention.StdCall)]
    static extern int CallNextHookEx(IntPtr hookHandle, int nCode, int wParam, ref GlobalKeyboardHookStruct lParam);




    #endregion

    #region Public Methods

    public int hookProc(int nCode, int wParam, ref GlobalKeyboardHookStruct lParam)
    {

        if (nCode >= 0)
        {
            Keys key = (Keys)lParam.vkCode;

            if (HookedKeys.Contains(key) == true)
            {
                KeyEventArgs kea = new KeyEventArgs(key);

                    if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && KeyUp != null)
                    {
                        KeyUp(this, kea);
                    }
                    else if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && KeyDown != null)
                    {
                        KeyDown(this, kea);
                    }
                    if (kea.Handled) return 1;


            }
        }

     return CallNextHookEx(hookHandle, nCode, wParam, ref lParam);
    }


    public void hook()
    {
            IntPtr hInstance = LoadLibrary("user32");
            hookHandle = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
    }


    public void unhook()
    {
        UnhookWindowsHookEx(hookHandle);
    }

    #endregion

    #region Constructors and Destructors

    public GlobalKeyboardHook()
    {
        hook();
    }

    ~GlobalKeyboardHook()
    {
        unhook();
    }

    #endregion

Answer 1

Try debugging your application with the “CallbackOnCollectedDelegate” MDA turned on (Debug -> Exceptions -> Managed Debugging Assistants -> check “CallbackOnCollectedDelegate”).

The common bug here is that the delegate for your hook procedure is automatically collected by the GC after you set the hook (it gets created as part of the P/Invoke marshaling to SetWindowsHookEx). After the GC collects the delegate, the program crashes when trying to call the callback. This would also explain the randomness.

If this is your issue, you’ll see an error like the following:

A callback was made on a garbage
collected delegate of type ‘…’.
This may cause application crashes,
corruption and data loss. When passing
delegates to unmanaged code, they must
be kept alive by the managed
application until it is guaranteed
that they will never be called.

Try keeping a reference to your hook procedure as a member in your class, e.g.:

public delegate int KeyboardHookProc(int nCode, int wParam, ref GlobalKeyboardHookStruct lParam);

public int hookProc(int nCode, int wParam, ref GlobalKeyboardHookStruct lParam)
{
    // ...
}

public void hook()
{
    _hookProc = new KeyboardHookProc(hookProc);
    IntPtr hInstance = LoadLibrary("user32");
    hookHandle = SetWindowsHookEx(WH_KEYBOARD_LL, _hookProc, hInstance, 0);
}

KeyboardHookProc _hookProc;