利用傳入的泛型建立並回傳泛型清單（List(Of T)）

2012-03-30

3611
0
2012-03-31

Dotblogs 的標籤：VB.Net ,隨手記

今天請 Member 練習把 DataTable 轉成 List，而且要做屬性<->欄位的對應，結果 member 搞了半天，跟我說遇到問題，他不知道要怎麼建立泛型清單，結果我明明記得應該是 CreateInstance 方法，但卻怎樣都想不起該怎麼做 ><。搞半天終於找到以前寫的 Sample Code，所以還是趕快筆記下來，不然下次又要找半天……

Module Module1

    Sub Main()
        Dim PersonList = ToGenericList(New Person())
        PersonList.Item(0).Name = "XYZ"
        PersonList.Item(1).Name = "Leo"
        For Each p In PersonList
            Console.WriteLine(p.Name)
        Next

        Console.ReadLine()
    End Sub

    Public Function ToGenericList(Of T)(ByVal entity As T) As List(Of T)
        Dim GenericList As New List(Of T)
        Dim p1 As T = CType(Activator.CreateInstance(GetType(T)), T)
        GenericList.Add(p1)
        Dim p2 As T = CType(Activator.CreateInstance(GetType(T)), T)
        GenericList.Add(p2)

        Return GenericList
    End Function

End Module

Public Class Person
    Public Name As String
    Public Age As Integer
End Class

程式碼重點就是：用 Activator.CreateInstance 就行啦！

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91 大提醒了更好的寫法，用泛型條件約束的方式，就不用特別再 New 一個物件當參數，大感謝~~ 程式碼修正如下：

Module Module1

    Sub Main()
        Dim PersonList = ToGenericList(Of Person)()
        PersonList(0).Name = "XYZ"
        PersonList(1).Name = "Leo"
        For Each p In PersonList
            Console.WriteLine(p.Name)
        Next

        Console.ReadLine()
    End Sub

    Public Function ToGenericList(Of T As New)() As IEnumerable(Of T)
        Dim GenericList As New List(Of T)
        GenericList.Add(New T)
        GenericList.Add(New T)

        Return GenericList
    End Function

End Module

Public Class Person
    Public Name As String
    Public Age As Integer
End Class

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沒什麼特別的~
不過是一些筆記而已

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