Question

在课堂之外，我希望能够以ReadOnly的身份访问CCTV.Camera.Brightness属性，但CCTV类中的方法应该能够修改Brightness属性。请问您如何实现这一目标？

我认为我需要添加一个公开某些属性并隐藏其他属性的接口，但我不确定实现。 [注意构造函数和main sub显然是为这个例子和测试而设计的。

Public Class CCTV

   Public Class Camera
       Public Property Name as String
       Public Property Brightness as Integer
   End Class

   Dim cameras as New Dictionary(Of String, Camera)
   Public Sub New()
      Dim cam As New Camera
      cam.Name = "driveway"
      cam.Brightness = 5
      cameras.Add(cam.Name, cam)
   End Sub

   Public Sub ChangeBrightness(value as Integer)
      cameras("driveway").Brightness = value
   End Sub

End Class

Sub main()
  Dim MyCCTV = new CCTV
  MyCCTV.ChangeBrightness(10)
  if MyCCTV("driveway").Brightness = 10 then Console.Write("Brightness is 10")
End Sub

Answer 1

获取getter并且属性的setter可以具有不同的可访问性修饰符。在这种情况下，您希望每个人都可以读取Brightness，但只有您信任的代码才能编写它。你这样做：

Public Class Camera
    Private _brightness As Integer

    Public Property Brightness As Integer
        Get
            Return _brightness
        End Get
        Friend Set(value As Integer)
            _brightness = Value
        End Set
    End Property

    '' etc...
End Class

请注意添加的Friend关键字，它限制了对Camera类所属的同一项目中的代码的访问权限。如果要限制只访问Camera类或其派生类中的代码，它也可以是Private或Protected。

Answer 2

在这种情况下不需要任何接口。您只需要以readonly方式创建属性。当您将属性设置为readonly时，假设该值将存储在私有变量中，并且此时应该更好地传递它或者方法或使用重载方法的subnew让我给你举个例子：

Public Class CCTV

Public Class Camera
    Private _Name As String
    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(ByVal value As String)
            _Name = value
        End Set
    End Property


    Private _Brightness As String
    Public ReadOnly Property Brightness() As String
        Get
            Return _Brightness
        End Get

    End Property
    ''' <summary>
    ''' Defautl sub new method
    ''' </summary>
    ''' <remarks></remarks>
    Sub New()

    End Sub
    ''' <summary>
    ''' second overload
    ''' </summary>
    ''' <param name="cameraName"></param>
    ''' <param name="brightness"></param>
    ''' <remarks></remarks>
    Sub New(ByVal cameraName As String, ByVal brightness As Integer)
        Me.Name = cameraName
        Me._Brightness = brightness
    End Sub

    ''' <summary>
    ''' Change brigthness
    ''' </summary>
    ''' <param name="value"></param>
    ''' <remarks></remarks>
    Public Sub setUpCameraBrightness(ByVal value As Integer)
        'take care to use private varibale so it will reflcet changes into propetry readonly
        Me._Brightness = value
    End Sub
End Class

Dim cameras As New Dictionary(Of String, Camera)
Public Sub New()
    'two differnet approach 
    'first overaload:
    Dim cam As New Camera()
    cam.Name = "yourcamname"
    cam.setUpCameraBrightness(10)
    cameras.Add(cam.Name, cam)



    ''second approch declarative value:
    Dim cam2 As New Camera("yourcamname", 10)
    cameras.Add(cam2.Name, cam2)

End Sub

Public Sub ChangeBrightness(value As Integer)
    cameras("driveway").setUpCameraBrightness(100)
End Sub

End Class

Sub main()
    Dim MyCCTV = New CCTV
    MyCCTV.ChangeBrightness(10)
    If MyCCTV("driveway").Brightness = 10 Then Console.Write("Brightness is 10")
End Sub

嵌套课程＆amp;只读属性

2 个答案: