是否可以在子類中分配一個ReadOnly變量？

Question

假設我有這樣的父類：

Public MustInherit Class Parent 

    ' ReadOnly instance variables: 
    Protected ReadOnly str1 As String 
    Protected ReadOnly str2 As String 
    Protected ReadOnly str3 As String 

    ' constructor: 
    Public Sub New() 
    End Sub 
End Class 

我想在子類的構造函數分配這些變量，我想他們是ReadOnly，使他們無法改變分配一次，像這樣的：

Public Class Child 
    Inherits Parent 

    ' constructor: 
    Public Sub New() 
      MyBase.New() 

      ' can't assign the ReadOnly variables here! 
      ' compile error: 'ReadOnly' variable cannot be the target of an assignment 
      Me.str1 = "asdf" 
      Me.str2 = "qwerty" 
      Me.str3 = "foobar" 
    End Sub 
End Class 

我怎樣才能做到這一點？如果不可能，爲什麼不呢？

Answer 1

通過它們傳遞給父類的構造：然後

Public MustInherit Class Parent 

    ' ReadOnly instance variables: 
    Protected ReadOnly str1 As String 
    Protected ReadOnly str2 As String 
    Protected ReadOnly str3 As String 

    ' constructor: 
    Public Sub New(s1 as String, s2 as String, s3 as String) 
     str1 = s1 
     str2 = s2 
     str3 = s3 
    End Sub 
End Class 

你的類可以這樣做：

Public Class Child 
    Inherits Parent 

    ' constructor: 
    Public Sub New(s1 as String) ' You can pass these through if needed 
      MyBase.New(s1, "qwerty", "foobar") 
    End Sub 
End Class