SetWindowsHookEx returns 0 when compiling for the .NET 4.0 framework in 32bit machines

Question

I'm trying to set a low level windows keyboard hook to grab three keys pressed even if the application is not in focus. To do this I'm calling SetWindowsHookEx as

// Create an instance of HookProc.
KeyboardHookProcedure = new HookProc(KeyboardHookProc);
//install hook
hKeyboardHook = SetWindowsHookEx(
    WH_KEYBOARD_LL,
    KeyboardHookProcedure,
    Marshal.GetHINSTANCE(
        Assembly.GetExecutingAssembly().GetModules()[0]),
    0);
//If SetWindowsHookEx fails.
if (hKeyboardHook == 0)
{
    //Returns the error code returned by the last unmanaged function called using platform invoke that has the DllImportAttribute.SetLastError flag set. 
    int errorCode = Marshal.GetLastWin32Error();
    //do cleanup
    Stop(false, true, false);
    //Initializes and throws a new instance of the Win32Exception class with the specified error. 
    throw new Win32Exception(errorCode);
}

This used to work on 32bit and 64bit machines using the .NET Framework 3.5 but after upgrading to the .NET Framework 4.0 stopped working on 32bit machines.

Does anyone know how to solve this so that I can use the 4.0 Framework and make this work on both 32bit and 64bit machines?

In .NET 4.0, SetWindowsHookEx returns 0 for me with an Invalid Hook Procedure error. — tofutim, Aug 07 '12 at 17:04

score 27 · Accepted Answer · edited Oct 20 '12 at 12:59

27

import the dll like this:

[DllImport("kernel32.dll")]
    public static extern IntPtr GetModuleHandle(string name);

then use

GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName)

to replace

Marshal.GetHINSTANCE(
    Assembly.GetExecutingAssembly().GetModules()[0]

edited Oct 20 '12 at 12:59

Kate Gregory

18,808
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answered Jun 29 '12 at 03:43

DsaIc

286
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1

Had the same problem and the solution was the suggested code change, using GetModuleHandle(...) to get the handle. – jensrodi Oct 28 '13 at 13:23
Thank you. This worked perfectly for me. I wasn't getting the main module. I was getting the current module and it was returning 0. – Vince Anzelone Mar 09 '15 at 04:20
Same problem here. Writing a quick window manager so I can press a key, drag a rectangle on the screen, and have the window snap to it. Dug up an old "GlobalHooks" module I wrote ages ago for .NET 2.0, and discovered SetWindowsHookEx was failing with zero. This solved the problem. I also made a note to myself that I need to loop over all keys calling GetAsyncKeyState, rather than just making a single call to GetKeyboardState, because it fails with threading issues, like it won't get modifier key states properly when other applications are in the foreground. GetAsyncKeyState must be used. – Triynko Jun 25 '15 at 02:21

score 2 · Answer 2 · answered Sep 22 '10 at 19:30

From the documentation for SetWindowsHookEx

hMod [in]
HINSTANCE
A 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.

So you should be passing in IntPtr.Zero for NULL

//install hook
  hKeyboardHook = SetWindowsHookEx(
    WH_KEYBOARD_LL,
    KeyboardHookProcedure,
    IntPtr.Zero,
    0);

score 1 · Answer 3 · answered Aug 30 '10 at 16:19

1

Solved it by targeting each platform separately. Configured VS to compile both a Win32 and a Win64 version and deploying on x86 and x64 machines their corresponding binary.

The Win32 or x86 runs on both 32bit and 64bit machines.

answered Aug 30 '10 at 16:19

eblacklight

183
1
1
7

score 0 · Answer 4 · edited May 23 '17 at 12:23

Hans Passant:

Any module handle will do since it doesn't actually get used for low-level hooks, no DLL needs to be injected to make them work. Some care in selecting one is required for .NET 4 since its CLR no longer fakes module handles for pure managed assemblies. A good one to use is the one you get out of pinvoking LoadLibrary("user32.dll") since it is always already loaded. You don't have to call FreeLibrary().

You'll need this declaration to call LoadLibrary:
[DllImport("kernel32", SetLastError=true, CharSet = CharSet.Auto)]
private static extern IntPtr LoadLibrary(string fileName);

SetWindowsHookEx returns 0 when compiling for the .NET 4.0 framework in 32bit machines

4 Answers4

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