如何使用泛型列表是发生在派生类实现一个共同的接口

Question

可以说我有一个通用的接口（VB.NET）：

Public Interface IBase(Of T As {IBase(Of T)}) 
    Property Parent() As T 

我有2类，实现接口

Public Class Derive1 
    Implements IBase(Of Derive1) 
    Public Property Parent() As Derive1 Implements IBase(Of Derive1).Parent 

Public Class Derive2 
    Implements IBase(Of Derive2) 
    Public Property Parent() As Derive2 Implements IBase(Of Derive2).Parent 

如何使用泛型列表，可以同时接受Derive1和Derive2这样的：

genList.Add(Derive1) 
genList.Add(Derive2) 

Answer 1

麦e Derive1和Derive2实现通用接口，然后创建该接口的列表。例如，假设您要迭代通用列表并使用CountChildren等方法，您可以在该列表中的Derive1和Derive2对象上执行该方法。首先，你要创建一个接口，这样的：

Public Interface ICalculations 
    Function CountChildren() As Integer 
End Interface

然后，你要建立Derive1和Derive2让他们实现这个接口。下面是可能的样子：

Public Class Derive1 
    Implements IBasicPortfolio(Of Derive1) 
    Implements ICalculations 
    Public Property Value() As Integer 
     Get 
      Return m_Value 
     End Get 
     Set 
      m_Value = Value 
     End Set 
    End Property 
    Private m_Value As Integer 
    Public Property [Next]() As Derive1 
     Get 
      Return m_Next 
     End Get 
     Set 
      m_Next = Value 
     End Set 
    End Property 
    Private m_Next As Derive1 
    Public Function CountChildren() As Integer 
     Return 1 + [Next].CountChildren() 
    End Function 
End Class 

Public Class Derive2 
    Implements IBasicPortfolio(Of Derive2) 
    Implements ICalculations 
    Public Property Value() As Integer 
     Get 
      Return m_Value 
     End Get 
     Set 
      m_Value = Value 
     End Set 
    End Property 
    Private m_Value As Integer 
    Public Property [Next]() As Derive1 
     Get 
      Return m_Next 
     End Get 
     Set 
      m_Next = Value 
     End Set 
    End Property 
    Private m_Next As Derive1 
    Public Function CountChildren() As Integer 
     Return 1 + [Next].CountChildren() 
    End Function 
End Class

然后您可以创建ICalculations的列表，它可以同时包含Derive1和Derive2对象：

Dim foo = New List(Of ICalculations)() 

foo.Add(New Derive1()) 
foo.Add(New Derive2()) 

For Each bar As var In foo 
    bar.CountChildren() 
Next