如何正确将DependencyProperty绑定到ViewModel属性并实现变更同步

你当前的实现存在潜在的同步失效问题，因为WPF依赖属性的赋值多数场景会直接调用SetValue方法，不会走CLR属性的Set逻辑，比如XAML赋值、动画修改、绑定源更新等场景下，你写在Set里的赋值代码不会执行，导致同步失败。以下是两种适配不同场景的规范解决方案：

方案1：View仅需和内部ViewModel双向同步（最常用） #

直接通过WPF原生绑定机制建立依赖属性和ViewModel属性的双向绑定，完全不需要手写同步逻辑：

第一步：修改View构造函数，添加DataContext变更监听 #

Public Sub New()
    InitializeComponent()
    AddHandler DataContextChanged, AddressOf OnDataContextChanged
End Sub

第二步：实现DataContext变更处理，建立双向绑定 #

Private Sub OnDataContextChanged(sender As Object, e As DependencyPropertyChangedEventArgs)
    ' 清除旧绑定避免冲突
    BindingOperations.ClearBinding(Me, FloorIDProperty)
    
    If TypeOf e.NewValue Is FloorViewModel Then
        ' 依赖WPF原生绑定机制自动处理双向同步
        Dim binding As New Binding(NameOf(FloorViewModel.FloorID)) With {
            .Source = e.NewValue,
            .Mode = BindingMode.TwoWay
        }
        SetBinding(FloorIDProperty, binding)
    End If
End Sub

第三步：还原依赖属性CLR包装为标准写法 #

删掉Set方法内自定义的赋值逻辑，保留标准结构即可：

Public Property FloorID As String
    Get
        Return CStr(GetValue(FloorIDProperty))
    End Get
    Set(value As String)
        SetValue(FloorIDProperty, value)
    End Set
End Property

方案2：需要支持外部给View的FloorID属性绑定/赋值 #

如果你的View需要暴露FloorID给外部调用/绑定，同时还要和内部ViewModel同步，可以使用依赖属性变更回调+ViewModel属性变更监听的方案：

第一步：给依赖属性注册变更回调 #

Public Shared FloorIDProperty As DependencyProperty = DependencyProperty.Register(
    "FloorID",
    GetType(String),
    GetType(FloorView),
    New FrameworkPropertyMetadata(Nothing, AddressOf OnFloorIDChanged))

' 依赖属性变更时同步到ViewModel
Private Shared Sub OnFloorIDChanged(d As DependencyObject, e As DependencyPropertyChangedEventArgs)
    Dim view As FloorView = CType(d, FloorView)
    Dim vm As FloorViewModel = TryCast(view.DataContext, FloorViewModel)
    If vm IsNot Nothing Then
        vm.FloorID = CStr(e.NewValue)
    End If
End Sub

第二步：监听ViewModel属性变更，同步回依赖属性 #

Public Sub New()
    InitializeComponent()
    AddHandler DataContextChanged, AddressOf OnDataContextChanged
End Sub

Private Sub OnDataContextChanged(sender As Object, e As DependencyPropertyChangedEventArgs)
    ' 移除旧ViewModel的事件监听避免内存泄漏
    If TypeOf e.OldValue Is INotifyPropertyChanged Then
        RemoveHandler CType(e.OldValue, INotifyPropertyChanged).PropertyChanged, AddressOf OnVmPropertyChanged
    End If
    ' 添加新ViewModel的事件监听
    If TypeOf e.NewValue Is INotifyPropertyChanged Then
        AddHandler CType(e.NewValue, INotifyPropertyChanged).PropertyChanged, AddressOf OnVmPropertyChanged
        ' 初始化同步一次属性值
        FloorID = CType(e.NewValue, FloorViewModel).FloorID
    End If
End Sub

Private Sub OnVmPropertyChanged(sender As Object, e As PropertyChangedEventArgs)
    If e.PropertyName = NameOf(FloorViewModel.FloorID) Then
        FloorID = CType(sender, FloorViewModel).FloorID
    End If
End Sub

第三步：同样使用标准的依赖属性CLR包装即可。 #

内容的提问来源于stack exchange，提问作者WPF learner