如何在 VBA 中评估 Or 语句？

Question

我只是想知道Or 条件语句在 VBA/VB6 中是如何工作的。基本上，如果我们有If A Or B Then，布尔表达式的求值顺序是什么？如果 A 为真，是否也评估 B？

Answer 1

以下是一些测试结果：

Public Sub DoTesting()

    ' Displays "Test1" followed by "Test2", so they're evaluated in order.
    ' Also, both expressions are evaluated even though Test1() is False.
    If Test1() And Test2() Then
    End If

    ' Displays "Test2" followed by "Test1", so they're evaluated in order.
    ' Also, both expressions are evaluated even though Test2() is True.
    If Test2() Or Test1() Then
    End If

    ' Displays "Test1" only. Test2() is not evaluated.
    If Test1() Then If Test2() Then Debug.Print ""

End Sub

Public Function Test1() As Boolean
    MsgBox "Test1"
    Test1 = False
End Function

Public Function Test2() As Boolean
    MsgBox "Test2"
    Test2 = True
End Function

因此，无论结果如何，Or 或 And 中的两个表达式总是按顺序计算。您可以使用If ... Then If ... Then 来实现简单的内联短路。