Subclassing and Hooking with Visual Basic

Caveats

This hook hampers system performance considerably because it intercepts many common events that occur in the system, such as changing a control’s focus or manipulating a window. Unlike the WH_SHELL hook, this hook works for all windows and not just the top-level unowned windows in the system. If you can solve a problem with the WH_SHELL hook instead of with the WH_CBT hook, by all means use the WH_SHELL hook. The WH_SHELL hook puts less of a strain on the system because not all window events are intercepted -- just those of top-level unowned windows.

If you want to use the HCBT_KEYSKIPPED code, you must install a WM_KEYBOARD hook. Likewise, if you want to use the HCBT_CLICKSKIPPED code, you must install a WM_MOUSE hook.

If you use the HCBT_KEYSKIPPED code to initiate an action for a keystroke, you should also test for either the WM_KEYUP or WM_KEYDOWN message and then initiate the action for one of these messages. Otherwise, the action will be performed twice, once for each message.

Most likely, when using the WH_CBT hook, you also will use one or more other hooks to augment it. When doing so, verify that you release each hook not only before the application ends, but also before it is reinstalled. You can install the WH_JOURNALPLAYBACK hook multiple times in a single CBT application’s lifetime. It is imperative that you release this hook after it is finished or it might seem as if your application has locked up.

There is an article in the Microsoft Developer Network (MSDN) ...