Asp.net 继承类以删除属性并更改方法逻辑

以下类在ASP.NET应用程序中用于从数据库结果集中读取货币并将其相加（例如，以美元显示总计加上以GB磅显示总计）。其工作方式如下：

读取货币ID值

如果货币ID已存在，请增加该货币的总额

如果货币ID不存在，请将其与其值一起添加到列表中

下一个

它使用

CurrencyID

属性作为每个唯一货币之间的区分符，效果很好。然而，现在很明显，

IsoCurrencySymbol

在默认情况下对于每种货币也是唯一的，因此实际上不需要

CurrencyID

所以。。。我想知道是否可以从此类继承并删除对

CurrencyID

的任何引用，从而使

CompareTo

方法改用

IsoCurrencySymbol

诀窍是保留广泛使用的现有类，但引入一个不需要

CurrencyID

的修改版本。请问可以这样做吗

<Serializable()> _
Public Class CurrencyCounter

    <Serializable()> _
    Private Class CurrencyType
        Implements IComparable

        Public IsoCurrencySymbol As String
        Public CurrencySymbol As String
        Public CurrencyID As Int16
        Public Amount As Decimal

        Public Function CompareTo(obj As Object) As Integer Implements System.IComparable.CompareTo
            If Not TypeOf (obj) Is CurrencyType Then
                Throw New ArgumentException("Object is not a currency type")
            Else
                Dim c2 As CurrencyType = CType(obj, CurrencyType)
                Return Me.CurrencyID.CompareTo(c2.CurrencyID)
            End If
        End Function

    End Class

    Private _Currencies As List(Of CurrencyType)

    Public Sub New()
        _Currencies = New List(Of CurrencyType)
    End Sub

    Private Sub AddStructToList(CurrencyID As Integer, IsoCurrencySymbol As String, CurrencySymbol As String, Amount As Decimal)
        If IsoCurrencySymbol <> String.Empty AndAlso Amount > 0 Then
            Dim s As New CurrencyType
            s.CurrencyID = CurrencyID
            s.IsoCurrencySymbol = IsoCurrencySymbol
            s.CurrencySymbol = CurrencySymbol
            s.Amount = Amount
            _Currencies.Add(s)
        End If
    End Sub

    Public Sub Add(CurrencyID As Integer, IsoCurrencySymbol As String, CurrencySymbol As String, Amount As Decimal)
        Dim ct As CurrencyType = _Currencies.Find(Function(obj) obj.CurrencyID = CurrencyID)
        If ct IsNot Nothing Then
            ct.Amount += Amount
        Else
            AddStructToList(CurrencyID, IsoCurrencySymbol, CurrencySymbol, Amount)
        End If
    End Sub

    Public Sub Clear()
        _Currencies.Clear()
    End Sub

    Public Function Count() As Integer
        Return _Currencies.Count
    End Function

    Public Function RenderTotals() As String
        ' ...
    End Function

End Class

_
公共类货币计数器
_
私有类CurrencyType
实现不可比较
公共等电流符号作为字符串
作为字符串的公共货币符号
公共货币ID为Int16
以十进制表示的公共金额
公共函数CompareTo（obj作为对象）作为整数实现System.IComparable.CompareTo
如果不是TypeOf（obj）是CurrencyType，则
抛出新ArgumentException（“对象不是货币类型”）
其他的
尺寸c2为CurrencyType=CType（obj，CurrencyType）
返回我.CurrencyID.CompareTo（c2.CurrencyID）
如果结束
端函数
末级
私有货币作为列表（货币类型）
公共分新（）
_货币=新列表（货币类型）
端接头
私有子AddStructList（CurrencyID为整数，IsoCurrencySymbol为字符串，CurrencySymbol为字符串，金额为十进制）
如果IsoCurrencySymbol字符串.Empty且金额>0，则
Dim s作为新的CurrencyType
s、 CurrencyID=CurrencyID
s、 等电流符号=等电流符号
s、 CurrencySymbol=CurrencySymbol
s、 金额=金额
_货币.添加（s）
如果结束
端接头
公共子加法（CurrencyID为整数，IsoCurrencySymbol为字符串，CurrencySymbol为字符串，金额为十进制）
按CurrencyType=\u currences.Find（函数（obj）obj.CurrencyID=CurrencyID）调整ct
如果ct不是什么，那么
ct.金额+=金额
其他的
AddStructList（CurrencyID、IsoCurrencySymbol、CurrencySymbol、Amount）
如果结束
端接头
公共分区清除（）
_货币
端接头
公共函数Count（）为整数
Return\u currences.Count
端函数
公共函数RenderTotals（）作为字符串
' ...
端函数
末级

不，你不能那样做。继承的关键在于确保所有派生类（如果没有其他派生类的话）至少与其基类共享同一个公共接口。如果要删除属性，则该属性不共享同一接口，因此不兼容，也不是继承的候选对象

若不能说派生类是基类的一种类型，那个么就不能使用继承。例如，我可以说汽车是一种交通工具，因此，如果我有一个汽车类，我可以让它从一个汽车类继承。然而，我不能说昆虫是一种交通工具。因此，即使它们共享大多数共同点，我也不能让昆虫类继承自vehicle类

此限制的原因是继承允许您将对象视为基本类型（通过类型转换）。例如：

Public Sub AddPassengerToVehicle(v As Vehicle)
    v.Passengers.Add(New Passenger())
End Sub

' ...

Dim auto As New Automobile()
Dim bug As New Insect()
AddPassengerToVehicle(auto) ' Works because an automobile is a type vehicle (inherits from vehicle)
AddPassengerToVehicle(bug) ' Can't possibly work (nor should it)

Public Class Vehicle
    Public Property Passengers As List(Of Passenger)
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Private _vehicle As New Vehicle()

    Public Property MaxSpeed() As Integer
        Get
            Return _vehicle.MaxSpeed
        End Get
        Set(value As Integer)
            _vehicle.MaxSpeed = value
        End Set
    End Property

    Public Function SpeedIsTooFast(speed) As Boolean
        Return _vehicle.SpeedIsTooFast(speed)
    End Function
End Class

Public Interface ISelfPoweredMovingThing
    Property MaxSpeed As Integer
    Function SpeedIsTooFast(speed As Integer) As Boolean
End Interface

Public Class SelfPoweredMovingThing
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Vehicle
    Inherits SelfPoweredMovingThing

    Public Property Passengers As List(Of Passenger)
End Class

Public Class Insect
    Inherits SelfPoweredMovingThing

    ' Anything else specific only to insects...
End Class

因此，如果您需要一个派生类来删除/隐藏其基类的一个成员，那么您的方向是错误的。在这种情况下，您需要创建一个全新的类，该类恰好具有非常相似的接口，但与第一个类没有直接关系，例如：

Public Sub AddPassengerToVehicle(v As Vehicle)
    v.Passengers.Add(New Passenger())
End Sub

' ...

Dim auto As New Automobile()
Dim bug As New Insect()
AddPassengerToVehicle(auto) ' Works because an automobile is a type vehicle (inherits from vehicle)
AddPassengerToVehicle(bug) ' Can't possibly work (nor should it)

Public Class Vehicle
    Public Property Passengers As List(Of Passenger)
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Private _vehicle As New Vehicle()

    Public Property MaxSpeed() As Integer
        Get
            Return _vehicle.MaxSpeed
        End Get
        Set(value As Integer)
            _vehicle.MaxSpeed = value
        End Set
    End Property

    Public Function SpeedIsTooFast(speed) As Boolean
        Return _vehicle.SpeedIsTooFast(speed)
    End Function
End Class

Public Interface ISelfPoweredMovingThing
    Property MaxSpeed As Integer
    Function SpeedIsTooFast(speed As Integer) As Boolean
End Interface

Public Class SelfPoweredMovingThing
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Vehicle
    Inherits SelfPoweredMovingThing

    Public Property Passengers As List(Of Passenger)
End Class

Public Class Insect
    Inherits SelfPoweredMovingThing

    ' Anything else specific only to insects...
End Class

如果您想要共享功能，例如上面示例中的

speedistofast

方法中的逻辑，那么有几种不同的方法可以实现。首先是生成包装器方法，这些方法只调用另一个类，例如：

Public Sub AddPassengerToVehicle(v As Vehicle)
    v.Passengers.Add(New Passenger())
End Sub

' ...

Dim auto As New Automobile()
Dim bug As New Insect()
AddPassengerToVehicle(auto) ' Works because an automobile is a type vehicle (inherits from vehicle)
AddPassengerToVehicle(bug) ' Can't possibly work (nor should it)

Public Class Vehicle
    Public Property Passengers As List(Of Passenger)
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Private _vehicle As New Vehicle()

    Public Property MaxSpeed() As Integer
        Get
            Return _vehicle.MaxSpeed
        End Get
        Set(value As Integer)
            _vehicle.MaxSpeed = value
        End Set
    End Property

    Public Function SpeedIsTooFast(speed) As Boolean
        Return _vehicle.SpeedIsTooFast(speed)
    End Function
End Class

Public Interface ISelfPoweredMovingThing
    Property MaxSpeed As Integer
    Function SpeedIsTooFast(speed As Integer) As Boolean
End Interface

Public Class SelfPoweredMovingThing
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Vehicle
    Inherits SelfPoweredMovingThing

    Public Property Passengers As List(Of Passenger)
End Class

Public Class Insect
    Inherits SelfPoweredMovingThing

    ' Anything else specific only to insects...
End Class

如果这样做，最好让两个类实现相同的公共接口，以便在必要时可以互换使用它们，例如：

Public Sub AddPassengerToVehicle(v As Vehicle)
    v.Passengers.Add(New Passenger())
End Sub

' ...

Dim auto As New Automobile()
Dim bug As New Insect()
AddPassengerToVehicle(auto) ' Works because an automobile is a type vehicle (inherits from vehicle)
AddPassengerToVehicle(bug) ' Can't possibly work (nor should it)

Public Class Vehicle
    Public Property Passengers As List(Of Passenger)
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Private _vehicle As New Vehicle()

    Public Property MaxSpeed() As Integer
        Get
            Return _vehicle.MaxSpeed
        End Get
        Set(value As Integer)
            _vehicle.MaxSpeed = value
        End Set
    End Property

    Public Function SpeedIsTooFast(speed) As Boolean
        Return _vehicle.SpeedIsTooFast(speed)
    End Function
End Class

Public Interface ISelfPoweredMovingThing
    Property MaxSpeed As Integer
    Function SpeedIsTooFast(speed As Integer) As Boolean
End Interface

Public Class SelfPoweredMovingThing
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Vehicle
    Inherits SelfPoweredMovingThing

    Public Property Passengers As List(Of Passenger)
End Class

Public Class Insect
    Inherits SelfPoweredMovingThing

    ' Anything else specific only to insects...
End Class

另一种选择是将通用功能划分为第三个类，然后将该类用作其他两个类的基础，例如：

Public Sub AddPassengerToVehicle(v As Vehicle)
    v.Passengers.Add(New Passenger())
End Sub

' ...

Dim auto As New Automobile()
Dim bug As New Insect()
AddPassengerToVehicle(auto) ' Works because an automobile is a type vehicle (inherits from vehicle)
AddPassengerToVehicle(bug) ' Can't possibly work (nor should it)

Public Class Vehicle
    Public Property Passengers As List(Of Passenger)
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Insect
    Private _vehicle As New Vehicle()

    Public Property MaxSpeed() As Integer
        Get
            Return _vehicle.MaxSpeed
        End Get
        Set(value As Integer)
            _vehicle.MaxSpeed = value
        End Set
    End Property

    Public Function SpeedIsTooFast(speed) As Boolean
        Return _vehicle.SpeedIsTooFast(speed)
    End Function
End Class

Public Interface ISelfPoweredMovingThing
    Property MaxSpeed As Integer
    Function SpeedIsTooFast(speed As Integer) As Boolean
End Interface

Public Class SelfPoweredMovingThing
    Public Property MaxSpeed As Integer

    Public Function SpeedIsTooFast(speed) As Boolean
        Return (speed > MaxSpeed)
    End Function
End Class

Public Class Vehicle
    Inherits SelfPoweredMovingThing

    Public Property Passengers As List(Of Passenger)
End Class

Public Class Insect
    Inherits SelfPoweredMovingThing

    ' Anything else specific only to insects...
End Class

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嗨，史蒂文。这是一个非常好的答案。非常感谢您花时间将其细分为我的门外汉级别：-）