Subclassing and Hooking with Visual Basic

A Thread-Specific Example

This example uses the WH_SHELL example that was presented in Chapter 17. Figure 21-2 shows the application’s user interface. As you can see, a checkbox labeled Discard Msg has been added to the example. When checked, it causes the WH_DEBUG hook to return a nonzero value, effectively preventing the target hook from being called. Otherwise, all messages will safely pass through this hook to the target hook.

Figure 21-2. A screenshot of the WH_SHELL/WH_DEBUG example

Table 21-1 presents the nondefault properties of the form and its controls.

Table 21-1. Nondefault Properties of the Form and Its Controls

Object	Property Name	Property Value
Form1	Name	Form2
Form1	Caption	“WH_SHELL Example”
Form1	Top	330
Form1	Left	105
Form1	Height	4710
Form1	Width	7095
Form2	Name	Form1
Form2	Caption	“NEW FORM”
Command Button1	Name	cmdHook
Command Button1	Caption	“hook”
Command Button1	Top	120
Command Button1	Left	120
Command Button1	Height	300
Command Button1	Width	915
Command Button2	Name	cmdUnhook
Command Button2	Caption	“unhook”
Command Button2	Top	780
Command Button2	Left	120
Command Button2	Height	300
Command Button2	Width	915
Command Button3	Name	cmdCreateWnd
Command Button3	Caption	“CreateWnd”
Command Button3	Top	3180
Command Button3	Left	120
Command Button3	Height	315
Command Button3	Width