Subclassing and Hooking with Visual Basic

A Thread-Specific Example

To better illustrate this hook’s function and position in the messaging system, I will modify the thread-specific example for the WH_CALLWNDPROC hook to incorporate the WH_CALLWNDPROCRET hook. As Figure 10-2 shows, the interface is similar to the example in Chapter 9, except for the output.

Figure 10-2. A screenshot of the WH_CALLWNDPROCRET example application

Table 10-1 defines the nondefault properties of the form and its controls.

Table 10-1. Nondefault Property Values for the Form and Its Controls

Control	Property	Value
Form	Caption	WH_CALLWNDPROC Hook Test
cmdSendMsg	Caption	SendMsg
cmdSendMsgTO	Caption	SendMsgTO
cmdPostMessage	Caption	PostMessage
cmdPostThreadMsg	Caption	PostThreadMsg
cmdSendMsgCB	Caption	SendMsgCB
cmdBroadcastMsg	Caption	BroadcastMsg
cmdSendDlgMsg	Caption	SendDlgMsg
cmdSendMsgNotify	Caption	SendMsgNotify
Frame1	Caption	CallWndProc
Text1	MultiLine	True

The code for this example is very similar to the code for the WH_CALLWNDPROC example. I will focus the following discussion on the changes to the code, starting with the Module2.bas module.

A single private member variable, bProcRetHook, was added to the code (BAS) module to hold the hook handle for the WH_CALLWNDPROCRET hook. The public and module-level variables declared in the BAS module are now:

Private hProcRetHook As Long Private hProcHook As ...