Question

我是VB.Net中的泛型和集合的新手。我编写了第一个创建自定义对象列表的类。虽然它似乎有用，但我相信我已经用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

这是我使用该课程的第一个小测试：

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

有关改进的具体问题是：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

是否有某种方法对类进行编码，以便可以表达allSub而无需同时指定.List - 以及表达它的某种方式，使得x将被识别为类型为Subscriber。

Answer 1

要完成这项工作，需要Subscribers实施IEnumerable(Of Subscribers)。实现可以转发到List字段

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

如何使VB.Net List类对调用者更灵活

1 个答案: