Question

Public Function Foo(ByRef a As AClass, _
                    Optional ByRef b As BClass = Nothing, _ 
                    Optional ByRef c As CClass = Nothing) As XClass

错误：可选参数必须指定默认值。

是Das吗？

Answer 1

这对我来说很好用空类编译。我似乎认为你在其他行或者参数类的定义中有错误。

Public Class Class1

    Public Function Foo(ByRef a As aclass, _
                        Optional ByRef b As bclass = Nothing, _
                        Optional ByRef c As cclass = Nothing) As xclass
        Return Nothing
    End Function

End Class

Public Class aclass    
End Class

Public Class bclass    
End Class

Public Class cclass    
End Class

Public Class xclass
End Class

Answer 2

如果这是您想要使用的模式，我建议您创建一个不需要这些参数的重载：

Public Function Foo(ByRef a As AClass) As XClass
    Return Foo(a, Nothing, Nothing)
End Function
Public Function Foo(ByRef a As AClass, ByRef b As BClass, ByRef c As CClass) As XClass
    '//Return XClass here
End Function

可选的ByRef - VB.NET中有错吗？

2 个答案: