SetWindowsHookEx (Compact 7)
3/12/2014
Installs an application-defined hook procedure. You would install a hook procedure to monitor the system for certain types of events.
Syntax
HHOOK WINAPI SetWindowsHookEx(
_In_ int idHook,
_In_ HOOKPROC lpfn,
_In_ HINSTANCE hMod,
_In_ DWORD dwThreadId
);
Parameters
idHook [in]
The type of hook procedure to be installed. This parameter can be only one of the following values in a single call.Value Description WH_KEYBOARD_LL
Installs a hook procedure that monitors low-level keyboard input events. For more information, see the LowLevelKeyboardProc callback function.
WH_MOUSE_LL
Installs a hook procedure that monitors low-level mouse input events. For more information, see the LowLevelMouseProc callback function.
- lpfn
[in] A pointer to the hook procedure. lpfn can only point to a hook procedure in the code associated with the current process.
- hMod
[in] Not used.
- dwThreadId
[in] Not supported; must be NULL.
Return Value
If the function succeeds, the return value is non-NULL handle but it is not a handle to the next Hook function in a chain. If the function fails, the return value is NULL. To get extended error information, call GetLastError.
Remarks
An error may occur if the dwThreadId parameter is not NULL.
HOOKPROCs are called in the context of the internal Message Queue architecture. In this context further processing by the message queue for the system is blocked until your application returns from HOOKPROC.
Before terminating, an application must call the UnhookWindowsHookEx function to free system resources associated with the hook.
The scope of hooks are system wide and not restricted to your specific application.
| Hook | Scope |
|---|---|
WH_KEYBOARD_LL |
System wide |
WH_MOUSE_LL |
System wide |
Successive calls to SetWindowsHookEx will fail after the first successful call. The Win32 version of CallNextHookEx is not supported and not required since a HOOK in this case is specific to the application. If you use a hook in a secondary thread, there must be a message pump associated with the secondary thread.