反序列化替换AppSettings实例时如何保留原有全部引用不失效？

方案1：全局单例+属性变更通知（WPF场景首选） #

这是最适配当前场景的方案，从根源上避免引用失效，同时兼容WPF数据绑定逻辑：

• 把AppSettings改造为全局单例，全应用生命周期内仅保留唯一实例，永远不直接替换该实例对象
• 给AppSettings和所有嵌套自定义类（比如你的Unit类）实现INotifyPropertyChanged接口，属性赋值时触发变更通知
• 调整反序列化逻辑：反序列化得到的结果仅作为临时数据源，把临时实例的所有属性值逐一写入已有的单例实例，而不是直接替换单例本身

你提到的手动维护赋值逻辑成本高的问题，实际场景中配置类的迭代频率极低，手写赋值逻辑的维护成本可以忽略。如果不想手动维护，用反射实现深度属性拷贝完全可行：配置加载属于极低频操作，一般仅在应用启动、用户手动导入配置时执行一次，哪怕遍历几十层嵌套属性，反射的耗时也不到1ms，不存在性能瓶颈。

示例代码 #

单例带通知的AppSettings实现

<Serializable()>
Public Class AppSettings
    Implements INotifyPropertyChanged

    ' 全局唯一实例
    Private Shared _instance As New AppSettings()
    Public Shared ReadOnly Property Instance As AppSettings
        Get
            Return _instance
        End Get
    End Property

    ' 私有构造函数，禁止外部创建新实例
    Private Sub New()
    End Sub

    Private _windowHeight As Integer = 600
    Public Property windowHeight As Integer
        Get
            Return _windowHeight
        End Get
        Set(value As Integer)
            _windowHeight = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(windowHeight)))
        End Set
    End Property

    Private _windowWidth As Integer = 800
    Public Property windowWidth As Integer
        Get
            Return _windowWidth
        End Get
        Set(value As Integer)
            _windowWidth = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(windowWidth)))
        End Set
    End Property

    Private _defaultLengthUnit As Unit = Units.meters
    Public Property defaultLengthUnit As Unit
        Get
            Return _defaultLengthUnit
        End Get
        Set(value As Unit)
            _defaultLengthUnit = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(defaultLengthUnit)))
        End Set
    End Property

    Private _defaultAngleUnit As Unit = Units.degrees
    Public Property defaultAngleUnit As Unit
        Get
            Return _defaultAngleUnit
        End Get
        Set(value As Unit)
            _defaultAngleUnit = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(defaultAngleUnit)))
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
End Class

带通知的Unit类实现

<Serializable()>
Public Class Unit
    Implements INotifyPropertyChanged

    Private _name As String
    Public Property Name As String
        Get
            Return _name
        End Get
        Set(value As String)
            _name = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(Name)))
        End Set
    End Property

    Private _abbreviation As String
    Public Property Abbreviation As String
        Get
            Return _abbreviation
        End Get
        Set(value As String)
            _abbreviation = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(Abbreviation)))
        End Set
    End Property

    Private _scale As Double
    Public Property Scale As Double
        Get
            Return _scale
        End Get
        Set(value As Double)
            _scale = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(Scale)))
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
End Class

修改后的反序列化逻辑

Public Sub LoadSettingsFromFile(ByVal filename As String)
    If Not File.Exists(filename) Then Return
    ' 反序列化得到临时实例
    Dim tempSettings As AppSettings
    Using sr As StreamReader = New StreamReader(filename)
        Dim xmls As XmlSerializer = New XmlSerializer(GetType(AppSettings))
        tempSettings = TryCast(xmls.Deserialize(sr), AppSettings)
    End Using
    If tempSettings Is Nothing Then Return

    ' 把临时实例的属性更新到单例，引用类型只更新内部属性不替换实例
    With AppSettings.Instance
        .windowHeight = tempSettings.windowHeight
        .windowWidth = tempSettings.windowWidth
        .defaultLengthUnit.Name = tempSettings.defaultLengthUnit.Name
        .defaultLengthUnit.Abbreviation = tempSettings.defaultLengthUnit.Abbreviation
        .defaultLengthUnit.Scale = tempSettings.defaultLengthUnit.Scale
        .defaultAngleUnit.Name = tempSettings.defaultAngleUnit.Name
        .defaultAngleUnit.Abbreviation = tempSettings.defaultAngleUnit.Abbreviation
        .defaultAngleUnit.Scale = tempSettings.defaultAngleUnit.Scale
    End With
End Sub

所有原有引用都指向同一个单例实例，属性更新后WPF绑定会自动收到通知刷新，完全不会出现引用断裂问题。

方案2：静态代理包装（最小改动现有代码） #

如果你不想改动现有所有引用AppSettings的业务逻辑，可以加一层静态代理层，所有对配置的访问都走代理，反序列化时只需要替换代理内部持有的实例即可：

Public NotInheritable Class AppSettingsProxy
    Private Shared _current As AppSettings = AppSettings.Instance
    ' 禁止外部实例化
    Private Sub New()
    End Sub
    Public Shared Property Current As AppSettings
        Get
            Return _current
        End Get
        Set(value As AppSettings)
            _current = value
        End Set
    End Property
End Class

原有代码中所有直接访问AppSettings的地方改为AppSettingsProxy.Current，反序列化后直接给AppSettingsProxy.Current赋值新实例即可，所有访问会自动指向新实例。注意该方案下WPF绑定路径需要同步修改为代理的属性，否则绑定仍会失效。

内容的提问来源于stack exchange，提问作者Justin8051