將資料傳遞迴事件源

使用通過引用傳遞的引數

事件可以定義要返回給呼叫者的 ByRef 引數：

Public Event BeforeSomething(ByRef cancel As Boolean)
Public Event AfterSomething()

Public Sub DoSomething()
    Dim cancel As Boolean
    RaiseEvent BeforeSomething(cancel)
    If cancel Then Exit Sub

    'todo: actually do something

    RaiseEvent AfterSomething
End Sub

如果 BeforeSomething 事件有一個處理程式將其 cancel 引數設定為 True，那麼當執行程式從處理程式返回時，cancel 將是 True 而 AfterSomething 將永遠不會被引發。

Private WithEvents foo As Something

Private Sub foo_BeforeSomething(ByRef cancel As Boolean)
    cancel = MsgBox("Cancel?", vbYesNo) = vbYes
End Sub

Private Sub foo_AfterSomething()
    MsgBox "Didn't cancel!"
End Sub

假設 foo 物件引用是在某處分配的，當 foo.DoSomething 執行時，一個訊息框提示是否取消，第二個訊息框僅在 No 選中時顯示未取消 。

使用可變物件

你也可以傳遞一個可變物件 ByVal 的副本，並讓處理程式修改該物件的屬性; 然後，呼叫者可以讀取修改後的屬性值並相應地執行操作。

'class module ReturnBoolean
Option Explicit
Private encapsulated As Boolean

Public Property Get ReturnValue() As Boolean
'Attribute ReturnValue.VB_UserMemId = 0
    ReturnValue = encapsulated
End Property

Public Property Let ReturnValue(ByVal value As Boolean)
    encapsulated = value
End Property

結合 Variant 型別，這可以用來建立非常明顯的方法來將值返回給呼叫者：

Public Event SomeEvent(ByVal foo As Variant)

Public Sub DoSomething()
    Dim result As ReturnBoolean
    result = New ReturnBoolean

    RaiseEvent SomeEvent(result)

    If result Then ' If result.ReturnValue Then
        'handler changed the value to True
    Else
        'handler didn't modify the value
    End If
End Sub

處理程式看起來像這樣：

Private Sub source_SomeEvent(ByVal foo As Variant) 'foo is actually a ReturnBoolean object
    foo = True 'True is actually assigned to foo.ReturnValue, the class' default member
End Sub