从父类

Question

我在VB.NET中构建一个将广泛使用类继承的应用程序，并将尽可能多的代码放入基类，包括数据库操作。我遇到的问题是如何从父类设置派生类的属性。我可以检索这些值，并设置非readonly属性的值而不会出现问题，但是有几种情况我想通过代码设置只读属性，但仍然不允许用户更改这些（修改日期/创建日期，例如）。我已经整理了一个显示问题的快速控制台应用程序;

父类：

Public Class clsParent
    Private _ParentInteger As Integer = 0
    Public Property ParentInteger As Integer
        Get
            Return _ParentInteger
        End Get
        Set(value As Integer)
            _ParentInteger = value
        End Set
    End Property

    Public Sub PrintProperties()
        Dim t As Type = Me.GetType
        Console.WriteLine("Object type: '{0}'", t.ToString)
        Dim propInfos As PropertyInfo() = t.GetProperties()
        Console.WriteLine("The number of properties: {0}", propInfos.Length)
        Console.WriteLine("------------------------------------------------------------")
        For Each propInfo In propInfos
            Dim readable As Boolean = propInfo.CanRead
            Dim writable As Boolean = propInfo.CanWrite

            Console.WriteLine("   Property name: {0}", propInfo.Name)
            Console.WriteLine("   Property type: {0}", propInfo.PropertyType)
            Console.WriteLine("   Read-Write:    {0}", readable And writable)
            Console.WriteLine("   Value:         {0}", propInfo.GetValue(Me))
            Console.WriteLine("------------------------------------------------------------")
        Next

    End Sub

    Public Sub TryWriteProperties()
        Dim t As Type = Me.GetType
        Dim propInfos As PropertyInfo() = t.GetProperties()

        For Each propInfo In propInfos
            Console.WriteLine("------------------------------------------------------------")
            Console.WriteLine("   {0}", propInfo.Name)
            Try
                Console.WriteLine("      Old Value:     {0}", propInfo.GetValue(Me))
                propInfo.SetValue(Me, CInt(propInfo.GetValue(Me)) + 100)
                Console.WriteLine("      New Value:     {0}", propInfo.GetValue(Me))
            Catch ex As Exception
                Console.WriteLine("      Failed to set new value: {0}", ex.Message)
            End Try
        Next
    End Sub
End Class

和孩子一样;

Public Class clsChild
    Inherits clsParent

    Dim _ChildWritableInteger As Integer = 5
    Public Property ChildWritableInteger As Integer
        Get
            Return _ChildWritableInteger
        End Get
        Set(value As Integer)
            _ChildWritableInteger = value
        End Set
    End Property

    Dim _ChildReadOnlyInteger As Integer = 10
    Public ReadOnly Property ChildReadOnlyInteger As Integer
        Get
            Return _ChildReadOnlyInteger
        End Get
    End Property
End Class

一个简单的子显示输出;

Sub Main()
    Dim x As New clsChild
    x.PrintProperties()
    Console.WriteLine("Waiting...")
    Console.ReadLine()
    Do Until Console.ReadLine = "x"
        x.TryWriteProperties()
        Console.WriteLine("Waiting...")
    Loop
End Sub

这（非常正确）向我显示错误＆＃34;无法设置新值：找不到属性集方法。＆＃34;当它试图设置＆＃34; ChildReadOnlyInteger＆＃34;属性。

Object type: 'ConsoleApplication1.clsChild'
The number of properties: 3
------------------------------------------------------------
   Property name: ChildWritableInteger
   Property type: System.Int32
   Read-Write:    True
   Value:         5
------------------------------------------------------------
   Property name: ChildReadOnlyInteger
   Property type: System.Int32
   Read-Write:    False
   Value:         10
------------------------------------------------------------
   Property name: ParentInteger
   Property type: System.Int32
   Read-Write:    True
   Value:         0
------------------------------------------------------------
Waiting...


------------------------------------------------------------
   ChildWritableInteger
      Old Value:     5
      New Value:     105
------------------------------------------------------------
   ChildReadOnlyInteger
      Old Value:     10
      Failed to set new value: Property set method not found.
------------------------------------------------------------
   ParentInteger
      Old Value:     0
      New Value:     100
Waiting...

我的问题是，什么是最好的方法，基类可以修改子类的属性或变量，而不会将属性公开显示为读/写，并且没有两个属性链接到同一个保持变量？

Answer 1

我希望我理解你的问题。您可以设置＆＃34; Set＆＃34;作为受保护的。

Class SomeName

    Private _someVariable As Integer

    Public Property SomeVariable As Integer
        Get
            Return _someVariable
        End Get
        Protected Set(value As Integer)
            _someVariable = value
        End Set
    End Property

End Class