Question

我们采取以下案例

Public MustInherit Class AnexaClass
    Inherits ObjectBase
    Private _proprietar As New ProprietarClass
    Public Property proprietar As ProprietarClass
        Get
            Return _proprietar
        End Get
        Set(value As ProprietarClass)
            _proprietar = value
            OnPropertyChanged("proprietar")
        End Set
    End Property
End Class

Public Class Anexa3Class
    Inherits AnexaClass

    Private _Proprietari As New ObservableCollection(Of ProprietarClass)
    Public Property Proprietari As ObservableCollection(Of ProprietarClass)
        Get
            Return _Proprietari
        End Get
        Set(value As ObservableCollection(Of ProprietarClass))
            _Proprietari = value
            OnPropertyChanged("Proprietari")
            If _Proprietari.Count > 0 Then
                Me.proprietar = _Proprietari(0) 'this line sets Proprietar to be the same as the first item of Proprietari and it works as it should be
            End If
        End Set
    End Property

Public MustInherit Class AnexaViewModel(Of AnexaT As {AnexaClass, New})
    Inherits ObjectBase

    Private _Anexa As New AnexaT
    Public Property Anexa As AnexaT
        Get
            Return _Anexa
        End Get
        Set(value As AnexaT)
            _Anexa = value
            OnPropertyChanged("Anexa")
        End Set
    End Property
    Public Sub ToXML()
        MsgBox(Anexa.proprietar.nume) 'at this point Anexa.proprietar is nothing
        MsgBox(Anexa.Proprietari(0).nume) ' but this is fine, even though Proprietari is only declared inside the derived class Anexa3Class
        ''Some other code''
    End Sub
End Class
Public Class Anexa3ViewModel
    Inherits AnexaViewModel(Of Anexa3Class)
End Class

我的程序实例化Anexa3ViewModel，然后设置Proprietari property将Proprietar设置为Proprietari(0)（当我调试时，这似乎工作正常），然后我调用{ {1}}通过命令按下按钮。内部ToXML ToXML内容无效，但Anexa.proprietar具有正确的值。

显然Anexa.Proprietari(0)属性丢失了它的值，或者存储了两个proprietar属性，一个用于我的基类，一个用于派生类。我认为只有通过遮蔽基本属性才能实现这一点，我不会这样做。我认为有一些继承概念让我无法理解。

有人可以对此有所了解吗？

澄清1 ：我知道如果我只是将一个项目添加到集合中，Proprietar的setter就不会起火。这不是我的问题，因为我立刻设置整个集合并且它的setter被触发，我可以看到Proprietari获得proprietar的正确值。问题在于它到达Proprietari(0)时会失去价值。

Answer 1

在没有看到你的应用程序的其余部分的情况下，最好的猜测是你有其他代码在Anexa3Class中为Proprietari集合添加值，而不是通过属性设置整个集合。

根据您的应用需求和设计，有一些潜在的解决方法。一种方法是处理Proprietari集合上的CollectionChanged事件：

Private WithEvents _Proprietari As New ObservableCollection(Of ProprietarClass)
Private Sub _Proprietari_CollectionChanged(sender As Object, e As System.Collections.Specialized.NotifyCollectionChangedEventArgs) Handles _Proprietari.CollectionChanged
    If Me.proprietar Is Nothing AndAlso e.Action = Specialized.NotifyCollectionChangedAction.Add Then
        Me.proprietar = e.NewItems(0)
    End If
End Sub

另一个可能的选择是将propietar更改为可覆盖的readonly属性并始终返回第0个值，但这可能会破坏OnPropertyChanged逻辑。

继承的属性在基类的方法中没有任何内容

1 个答案: