SetWindowsHookEx in C#

SetWindowsHookEx specifies the last two parameters thusly:

• hMod

[in] Handle to the DLL containing the hook procedure pointed to by the lpfn parameter. The hMod parameter must be set to NULL if the dwThreadId parameter specifies a thread created by the current process and if the hook procedure is within the code associated with the current process.

• dwThreadId

[in] Specifies the identifier of the thread with which the hook procedure is to be associated. If this parameter is zero, the hook procedure is associated with all existing threads running in the same desktop as the calling thread.

I'm not sure you can use a .NET dll in the manner required, but you can certainly try.

Grab hMod via Marshal.GetHINSTANCE(typeof(Form1).Module) and dwThreadId via Process.Threads. Alternatively, set dwThreadId to 0 if you want a global hook (ie. a hook for all GetMessage() calls in the current desktop) but beware of the performance penalties.

The following suggests this won't work:

"Global hooks are not supported in the .NET Framework. Except for the WH_KEYBOARD_LL low-level hook and the WH_MOUSE_LL low-level hook, you cannot implement global hooks in the Microsoft .NET Framework."

From "How to set a Windows hook in Visual C# .NET"

I believe you need to P/Invoke GetModuleHandle and use the handle it returns for the third parameter of SetWindowsHookEx. I also believe 0 is correct for the fourth parameter, as you don't want to hook any one specific thread in the third-party application.

If this doesn't work for you, SetWindowsHookEx on MSDN might point you in the right direction.

I don't know but if you're using parameter values which specify that you want to, as the API helps says, "inject a DLL into another process", then for all I know it might work only if you write an unmanaged DLL from which to call it.

I know that this is an old question but I'm hoping that there is still someone who will find this useful. I think that you are mixing up int and IntPtr

[System.Runtime.InteropServices.DllImport("user32.dll")]
static extern int CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);