vb.net - 如何让 VB.Net List 类对调用者更灵活

Question

我是 VB.Net 中的泛型和集合的新手。我已经编写了我的第一个创建自定义对象列表的类。虽然它似乎有效，但我相信我已经以一种粗略的方式完成了它，我想知道如何为需要调用它的代码改进它。这是列表类的基本部分:

Public Class Subscribers
    Public List As New List(Of Subscriber)
    Public Sub New()
        Dim sConnDatabase As String = ConfigurationManager.ConnectionStrings("DatabaseConnString").ConnectionString
        Dim connection As New SqlConnection(sConnDatabase)
        Dim cmd As SqlCommand
        cmd = New SqlCommand("SELECT * FROM dbo.Subscriber_v", connection)
        cmd.CommandType = CommandType.Text
        connection.Open()
        Dim objReader As SqlDataReader = cmd.ExecuteReader()
            Do While objReader.Read()
            Dim id As Integer = objReader("SubscriberID")
            Dim s As Subscriber = New Subscriber(id)
            List.Add(s)
        Loop
        objReader.Close()
        connection.Close()
    End Sub
End Class

这是我使用该类的第一个小测试:

Dim n As String
Dim d As Integer

Dim allSubs As New Subscribers()
For Each Subscriber In allSubs.List
    n = Subscriber.SubscriberName
    d = Subscriber.DaysUntilExpired.ToString()
Next

关于改进的一个具体问题是:如何使调用者能够编写如下代码:

For Each x In allSubs
n = x.SubscriberName
d = x.DaysUntilExpired.ToString()
Next

是否有某种方式对类进行编码，以便可以在不必同时指定 .List 的情况下表达 allSubs - 以及某种表达方式，以便将 x 识别为订阅者类型。

Answer 1

要完成这项工作需要有Subscribers实现 IEnumerable(Of Subscribers) .实现可以直接转发到List场

Public Class Subscribers Implements IEnumerable(Of Subscriber)
  Public Function GetEnumerator() As IEnumerator(Of Subscriber) _  
    Implements IEnumerable(Of Subscriber).GetEnumerator

    Return List.GetEnumerator()
  End Function

  Private Function GetEnumerator1() As IEnumerable _
    Implements IEnumerable.GetEnumerator

    Return List.GetEnumerator()
  End Function
End Class