如何在VB6中编写回调？

Question

如何在VB6中编写回调函数？我知道AddressOf让你的函数获取Long中的地址。但是，如何使用内存地址调用函数？谢谢！

Answer 1

我不知道你想要做什么。

到invert control，只需在类中创建回调函数即可。然后使用该类的一个实例（一个对象）进行回调。

• 如果您需要在运行时在不同的例程之间切换，请将不同的类实现相同的接口 - strategy pattern。
• 恕我直言AddressOf是太复杂和风险使用这种方式。

AddressOf应只有来，如果你需要register callback functions与Windows API使用。

Answer 2

This post在vbforums.com上给出了一个如何使用AddressOf和CallWindowProc函数来执行回调过程的例子。从岗位

代码：

Private Declare Function CallWindowProc _ 
Lib "user32.dll" Alias "CallWindowProcA" (_ 
ByVal lpPrevWndFunc As Long, _ 
ByVal hwnd As Long, _ 
ByVal msg As Long, _ 
ByVal wParam As Long, _ 
ByVal lParam As Long) As Long 

Private Sub ShowMessage(_ 
msg As String, _ 
ByVal nUnused1 As Long, _ 
ByVal nUnused2 As Long, _ 
ByVal nUnused3 As Long) 
    'This is the Sub we will call by address 
    'it only use one argument but we need to pull the others 
    'from the stack, so they are just declared as Long values 
    MsgBox msg 
End Sub 

Private Function ProcPtr(ByVal nAddress As Long) As Long 
    'Just return the address we just got 
    ProcPtr = nAddress 
End Function 

Public Sub YouCantDoThisInVB() 
    Dim sMessage As String 
    Dim nSubAddress As Long 

    'This message will be passed to our Sub as an argument 
    sMessage = InputBox("Please input a short message") 
    'Get the address to the sub we are going to call 
    nSubAddress = ProcPtr(AddressOf ShowMessage) 
    'Do the magic! 
    CallWindowProc nSubAddress, VarPtr(sMessage), 0&, 0&, 0& 
End Sub