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尝试从带有参数的模块类调用子方法时出现错误 438

分类: 技术问答 • 2022-05-23 18:26:01
问题描述：

我明白了

错误 438:对象不支持此属性或方法

error 438 : Object does not support this property or method

尝试运行以下代码时.你能帮我解决这个问题吗?

when trying to run the following code. Could you help me with that please?

我的宏代码:

Sub test() 
   Dim upList As New ListRoot
   upList.msg 'this one works fine 

   Dim g As New Gradient
   upList.AppendRoot g 'line that raises the issue
End Sub

我的模块类代码:

Public Sub AppendRoot(grad As Gradient)
    If IsEmpty(content.content) Then
       Set content.content = grad
    Else
       content.Append (grad)
    End If
End Sub

Public Sub msg()
    MsgBox "HEY"
End Sub

我已经尝试了我的方法的不同调用:

I have already tried different calls of my method: 

upList.AppendRoot(g) 
Call upList.AppendRoot(g)

和上面引用的那个.没有工作.

and the one that is quoted above. None works.

答

注意调用子/函数不返回值必须不带括号调用:

Note that calling a sub/function without returning a value must be called without parenthesis:

content.Append grad

如果函数返回某个值，则必须添加括号

If the function returns some value then parenthesis must be added

ReturnValue = content.Append(grad)

但是，如果您将括号添加到不返回像您那样返回任何值的子/函数

But if you add parenthesis to a sub/function that does not return any value like you did

content.Append (grad)

... 强制变量 grad 被提交 ByVal 而 ByRef 是提交它们的标准方法.因此，通过在此处添加括号，您可以将 ByRef 更改为 ByVal(您还可以看到函数/子名称和括号之间有一个空格).

… that forces the variable grad to be submitted ByVal while ByRef is the standard method to submit them. So by adding parenthesis here you change from ByRef to ByVal (you can also see that there is a space between the function/sub name and the parenthesis).

示例:

Sub TestFunction(Param1, Param2, Param3) 'all 3 parameters are ByRef by default in VBA (not in VB.NET!)

End Sub

调用这个函数的一些例子:

Some examples to call this function:

'submit 3 parameters ByRef, don't return anything
TestFunction Param1, Param2, Param3 
TestFunction(Param1, Param2, Param3) 'throws error

'submit 3 parameters ByRef, return a Value
ReturnValue = TestFunction(Param1, Param2, Param3) 
ReturnValue = TestFunction Param1, Param2, Param3   'throws error 

'submit parameters 1 and 3 ByVal and 2 ByRef, don't return anything
TestFunction (Param1), Param2, (Param3) 

'submit parameters 1 and 3 ByVal and 2 ByRef, return a Value
ReturnValue = TestFunction((Param1), Param2, (Param3))

虽然有 3 个参数，但如果在不应该出现的位置添加括号，它会抛出错误，但只有一个参数会更困难:

While with 3 parameters it will throw an error if you add parenthesis where they should not be, it will be more difficult with only one parameter:

TestFunction Param1   'correct
TestFunction (Param1) 'this threw an error with 3 parameters, but does not throw an error 
                      'with one parameter instead it changes behavior ByRef to ByVal
ReturnValue = TestFunction(Param1) 'correct
ReturnValue = TestFunction Param1  'throws error

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