Question

我有一个扩展方法，可以很好地将对象转换为我的表单对象。

'Copy an object to a form object
<Extension()> _
Public Function FromModel(ToObject As BaseFormObject, ByRef FromObject As Object) As Boolean

    ToObject = FromObject

    Return True
End Function

我想为对象列表做同样的事情。

'Copy a list of objects to form objects
<Extension()> _
Public Function FromModelList(ToList As List(Of BaseFormObject), ByRef FromList As List(Of Object)) As Boolean

    For Each FromItem As Object In FromList
        'Create a new BaseFormObject for every item in FromList, Add it to our From List
        Dim newFormObject = New BaseFormObject()
        newFormObject.FromModel(FromItem)
        ToList.Add(newFormObject)
    Next

    Return True
End Function

创建新的List（Of BaseFormObject）不允许我访问方法“FromModelList”。这样做的正确方法是什么？

Answer 1

您的代码运行正常。

我创建了这段代码：

    Dim lst As New List(Of BaseFormObject)

当我输入lst.

时，我获得了扩展成员

我将在这里发表意见，并建议你实际上并没有实例化List(Of BaseFormObject)，而是List(Of ActualFormObject)之类的地方ActualFormObject继承BaseFormObject }}

所以如果我使用这段代码：

    Dim lst As New List(Of ActualFormObject)

然后你没有得到扩展成员。如果这是你所希望的，那么很容易解决。

将您的代码更改为：

<Extension()> _
Public Function FromModelList(Of T As {New, BaseFormObject})(ToList As List(Of T), ByRef FromList As List(Of Object)) As Boolean
    For Each FromItem As Object In FromList
        'Create a new BaseFormObject for every item in FromList, Add it to our From List
        Dim newFormObject = New T()
        newFormObject.FromModel(FromItem)
        ToList.Add(newFormObject)
    Next
    Return True
End Function

然后在子类列表上获得扩展成员。

VB中List（Of Object）的扩展方法

1 个答案: