将 Class 属性设为 Default 和 Shared

Question

我有一个名为“PartTypes”的类，其中包含一个“PartType”对象的共享列表。我在 PartTypes 类中有一个“Item”属性，它按名称检索共享列表中的 PartType。

在我的主要代码中，我希望能够说类似PartTypes("ItemX") 而不是PartTypes.Item("ItemX")。但是，我不知道如何使共享的“项目”属性也成为我班级的默认属性。

这是我想要做的一个简化和浓缩的版本，使用 String 列表而不是 PartType 列表：

Sub MainCode
    'How I have to do it now:
    oPartType = PartTypes.Item("Type1")

    'How I'd like to do it:
    oPartType = PartTypes("Type1")
End Sub

Class PartTypes
    Private Shared _PartTypes As New List(Of String)

    'Initialize global list of PartTypes:
    Shared Sub New
        _PartTypes.Add("Type1")
        _PartTypes.Add("Type2")
    End Sub

    'Property I want to be the "default":
    Public Shared ReadOnly Property Item(Name As String) As String
        Get
            If _PartTypes.Contains(Name) Then
                Return Name
            Else
                Return ""
            End If
        End Get
    End Property
End Class

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~ ～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～ ~~~~~~

如果您想知道我为什么要这样做，这里有一个扩展版本，应该可以更好地了解我实际上是如何使用 PartTypes 类的（但您不需要消化所有除非您愿意，否则适用于上述简化版本的解决方案可能适用于实际情况）：

Function SetUpType(TestTypeName As String) As PartType
    If PartTypes.IsType(TestTypeName) Then
        Dim oPartType As PartType

        'How I have to get the PartType object:
        oPartType = PartTypes.Item(TestTypeName)

        'How I'd like to get the PartType object:
        'oPartType = PartTypes(TestTypeName)

        'Set up oPartType:
        '...

        Return oPartType
    Else
        Return New PartType
    End If
End Function

Class PartType
    Public Name As String
    Public [Class] As String
    'Other properties of a PartType:
    '...
End Class

Class PartTypes
    Private Shared _PartTypes As New List(Of PartType)

    'Initialize global list of PartTypes:
    Shared Sub New
        Add("Type1","ClassA")
        Add("Type2","ClassA")
        Add("Type3","ClassB")
        Add("Type4","ClassC")
    End Sub

    Private Shared Function Add(Name As String, [Class] As String) As PartType
        Dim oPartType As New PartType
        oPartType.Name = Name
        oPartType.Class = [Class]

        _PartTypes.Add(oPartType)
        Return oPartType
    End Function

    'Property I want to be the "default":
    Public Shared ReadOnly Property Item(Name As String) As PartType
        Get
            For Each oPartType As PartType In _PartTypes
                If oPartType.Name = Name Then Return oPartType
            Next

            'If Type not found...
            Return New PartType
        End Get
    End Property

    'Examples of other PartTypes functions:
    Public Shared Function IsType([TypeName] As String) As Boolean
        For Each oPartType As PartType In _PartTypes
            If oPartType.Name = [TypeName] Then Return True
        Next

        'If Type not found...
        Return False
    End Function
End Class

Answer 1

您不能在类型本身上拥有Shared 默认属性 - 它必须是该类的实例。为了使Item属性默认，添加Default到属性：

Class PartTypes
    Default Public ReadOnly Property Item(Name As String) As String
        Get
            '...
        End Get
    End Property
End Class

用法：

Dim pt = New PartTypes()
Dim x = pt("Type1")