Subclassing and Hooking with Visual Basic

Global Subclassing

Global subclassing revolves around the same principles as instance subclassing. With global subclassing, though, we are going to go one level deeper before performing the subclassing. By this I mean that the modifications to the window procedure function pointer will occur in the class itself, not the individual window created from the class. Only those windows created from the class after the subclassing has occurred will use the new subclassed window procedure. When I mention subclassing in this section, I am referring to global subclassing.

Tip

Instance subclassing affects a specific window and its window procedure. Global subclassing affects every window created from a window class that has had its class window procedure modified.

Unlike instance subclassing, global subclassing can capture the window creation messages -- and, more specifically, WM_CREATE and WM_NCCREATE. When a window is created, the WM_NCCREATE message is sent first to the window to finish creating its nonclient area in memory. The WM_CREATE message is sent next to finish creating the window’s client area in memory. Note that the window is still not displayed on the screen at this point. Other messages still need to be sent to the window to position, size, and paint it on the desktop.

The reason that instance subclassing cannot capture these messages is that when instance subclassing occurs, the window has already been created. Therefore, the window creation messages have already been ...