如何在VB6中編寫回調？

Question

如何在VB6中編寫回調函數？我知道AddressOf讓你的函數獲取Long中的地址。但是，如何使用內存地址調用函數？謝謝！

Answer 1

我不知道你想要做什麼。

到invert control，只需在類中創建回調函數即可。然後使用該類的一個實例（一個對象）進行回調。

• 如果您需要在運行時在不同的例程之間切換，請將不同的類實現相同的接口 - strategy pattern。
• 恕我直言AddressOf是太複雜和風險使用這種方式。

AddressOf應只有來，如果你需要register callback functions與Windows API使用。

Answer 2

This post在vbforums.com上給出了一個如何使用AddressOf和CallWindowProc函數來執行回調過程的例子。從崗位

代碼：

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