C# Signature:

[DllImport("user32.dll")]
static extern IntPtr SetWindowsHookEx(HookType hook, HookProc callback,
   IntPtr hMod, uint dwThreadId);

User-Defined Types:

A HookType constant specifying the type of hook to install.

A HookProc delegate representing the hook procedure method.

Notes:

This will enable you to install application hooks. However, you cannot implement global hooks in Microsoft .NET Framework. To install a global hook, a hook must have a native dynamic-link library (DLL) export to inject itself in another process that requires a valid, consistent function to call into. This requires a DLL export, which .NET Framework does not support. Managed code has no concept of a consistent value for a function pointer because these function pointers are proxies that are built dynamically.

Tips & Tricks:

Remember to keep the HookProc delegate alive manually, otherwise the garbage collector will clean up your hook delegate eventually, resulting in your code throwing a System.NullReferenceException.

Rememeber to call CallNextHookEx

Sample Code:

// this sample installs a keyboard hook

using System.Windows.Forms;
public class MyClass
{
     private HookProc myCallbackDelegate = null;

     public MyClass()
     {
     // initialize our delegate
     this.myCallbackDelegate = new HookProc(this.MyCallbackFunction);

     // setup a keyboard hook
     SetWindowsHookEx(HookType.WH_KEYBOARD, this.myCallbackDelegate, IntPtr.Zero, AppDomain.GetCurrentThreadId());
     }

     [DllImport("user32.dll")]
     protected static extern IntPtr SetWindowsHookEx(HookType code, HookProc func, IntPtr hInstance, int threadID);

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

     private IntPtr MyCallbackFunction(int code, IntPtr wParam, IntPtr lParam)
     {
    if (code < 0) {
        //you need to call CallNextHookEx without further processing
        //and return the value returned by CallNextHookEx
        return CallNextHookEx(IntPtr.Zero, code, wParam, lParam);
    }
     // we can convert the 2nd parameter (the key code) to a System.Windows.Forms.Keys enum constant
     Keys keyPressed = (Keys)wParam.ToInt32();
     Console.WriteLine(keyPressed);
    //return the value returned by CallNextHookEx
    return CallNextHookEx(IntPtr.Zero, code, wParam, lParam);
     }
}

Alternative Managed API:

Do you know one? Please contribute it!

SetWindowsHookEx on MSDN

MSDN example of a mouse hook in C#: http://support.microsoft.com/default.aspx?scid=kb;en-us;318804#3

MSDN article on hooks in .NET: http://msdn.microsoft.com/msdnmag/issues/02/10/CuttingEdge/

MSDN article on KeyboardProc: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/winui/windowsuserinterface/windowing/hooks/hookreference/hookfunctions/keyboardproc.asp

Please edit this page!

Do you have...

• helpful tips or sample code to share for using this API in managed code?
• corrections to the existing content?
• variations of the signature you want to share?
• additional languages you want to include?

Select "Edit This Page" on the right hand toolbar and edit it! Or add new pages containing supporting types needed for this API (structures, delegates, and more).