Subclassing and Hooking with Visual Basic

A Thread-Specific Example

The example presented here shows in more detail how to set up and use this hook. A single window is created in this example, which is shown in Figure 9-2. Table 9-1 defines the nondefault properties of the form and its controls. This window has a hook and an unhook button in the CALLWNDPROC frame. You use these buttons to install and remove the hook.

Table 9-1. 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
cmdSendMsgCB	Caption	SendMsgCB
cmdBroadcastMsg	Caption	BroadcastMsg
cmdSendDlgMsg	Caption	SendDlgMsg
Frame1	Caption	CallWndProc
Text1	MultiLine	True

Each button’s functionality is defined as follows:

SendMsg

Calls the SendMessage function.

SendMsgNotify

Calls the SendNotifyMessage function.

SendMsgTO

Calls the SendMessageTimeout function.

SendMsgCB

Calls the SendMessageCallback function. The callback function is called DummyCallback and is located in the Module2.bas file.

SendDlgMsg

Calls the SendDlgItemMessage function.

BroadcastMsg

Calls the BroadcastSystemMessage function.

PostMessage

Calls the PostMessage function.

You use the text box on this window to display the values of parameters passed to the WH_CALLWNDPROC filter function.

Figure 9-2. Screenshot of the WH_CALLWNDPROC ...