VB5.0与Windows API 间的呼叫技巧

al hmod As Long, _
ByVal dwThreadId As Long) As Long

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Hook有很多种，如KeyBoard Hook, Mouse Hook, JournalRecord Hook等，所以第
一个参数指明了要哪一种Hook，第二个参数便是Hook Procedure所在，也就是方才所说
"自动执行某一段Function的功能"中的那一个Function，这个Function的名称可以随意
给定，但有一定的参数传递规则，例如：
hnexthookproc = SetWindowsHookEx(WH_KEYBOARD, _
AddressOf MyKBHFunc, App.Hinstance, 0)
如此设定则每当按任一个键时，程式自动会去执行 MyKBHFunc。这个Hook Function
是由我们所定义，但是它是由Window自动去呼叫，而不是由我们的程式呼叫，这类的
Function就叫CallBack Function。

以上面的例子来说，这个CallBack Function定义如下：
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Public Function MyKBHFunc(ByVal iCode As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
MyKBHFunc = 0
If iCode < 0 Then
MyKBHFunc = CallNextHookEx(hnexthookproc, iCode, wParam, lParam)
Exit Function
End If
''侦测 有没有按到PrintScreen键
If wParam = vbKeySnapshot Then
MyKBHFunc = 1
Debug.Print "haha"
End If
End Function
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这个KeyBoard Hook Function的目的主要是想拦截有没有按到Print Screen这个键
，这个键不会在Form的KeyDown, KeyPress, KeyUp Event中作用，所以只好透过KeyBoa
rd Hook去拦截。而CallBack Function放的位置有规定，一个是要与呼叫SetWindowsHo
okEx() 的地方在同样的一个Project，另外，它只能存在於.BAS档，不能放在其他地方
。KeyBoard Hook的程式於范五。

范例五
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''以下程式於Hook.bas
Declare Function SetWindowsHookEx Lib "user32" Alias _
"SetWindowsHookExA" (ByVal idHook As Long, ByVal lpfn As Long, _
ByVal hmod As Long, ByVal dwThreadId As Long) As Long
Declare Function UnhookWindowsHookEx Lib "user32" _
(ByVal hHook As Long) As Long
Declare Function CallNextHookEx Lib "user32" (ByVal hHook As Long, _
ByVal ncode As Long, ByVal wParam As Long, lParam As Any) As Long

Public hnexthookproc As Long
Public Const HC_ACTION = 0
Public Const WH_KEYBOARD = 2

Public Sub UnHookKBD()
If hnexthookproc 0 Then
UnhookWindowsHookEx hnexthookproc
hnexthookproc = 0
End If
End Sub
Public Function EnableKBDHook()
If hnexthookproc 0 Then
Exit Function
End If
hnexthookproc = SetWindowsHookEx(WH_KEYBOARD, AddressOf _
MyKBHFunc, App.Hinstance, 0)
If hnexthookproc 0 Then
EnableKBDHook = hnexthookproc
End If
End Function
Public Function MyKBHFunc(ByVal iCode As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
''这三个参数是固定的，不能动，而MyKBHFunc这个名称只要和
''SetWindowsHookex()中 AddressOf後的名称一样便可，不一定叫什麽
MyKBHFunc = 0
If iCode < 0 Then
MyKBHFunc = CallNextHookEx(hnexthookproc, iCode, wParam, lParam)
Exit Function
End If
If wParam = vbKeySnapshot Then ''侦测 有没有按到PrintScreen键
MyKBHFunc = 1
Debug.Print "haha"
End If
End Function
''以下程式於Form
Private Sub Form_Load()
Call EnableKBDHook
End Sub

Private Sub F