Newtonsoft.Json反序列化时如何传入ExchangeClass参数初始化对象？

问题 #

我通常通过以下方式创建BasicSimpleOrder对象：

Public Shared Function createBasicSimpleOrder(ammountOfQuoteCurrencyBeingOrdered As Decimal, priceInBasecoin As Decimal, Base As String, Quote As String, exchangeObject As ExchangesClass, isSellingInsteadOfBuying As Boolean, customIdentifier As String) As BasicSimpleOrder
    Dim exchangeString = exchangeObject.ExchangeStringName
    Dim a = New BasicSimpleOrder(ammountOfQuoteCurrencyBeingOrdered, priceInBasecoin, Base, Quote, exchangeString, isSellingInsteadOfBuying, customIdentifier)
    a.initializeComplexObjects(exchangeObject)
    Return a
End Function

其中exchangeObject As ExchangesClass是BasicSimpleOrder中唯一的非基元类型成员，我会在设置基元只读属性后调用initializeComplexObjects方法完成复杂对象初始化：

Public Sub initializeComplexObjects(exchangeObject As ExchangesClass)
    _exchangeObject = exchangeObject
    If exchangeObject Is Nothing Then Exit Sub
    Dim mark = CoinClass.MarketBaseQuoted(exchangeObject.ExchangeStringName, Base, Quote)
    If mark Is Nothing Then Exit Sub
    setMarket(mark)
End Sub

现在需要反序列化包含BasicSimpleOrder派生类的futureStateForGrid对象，使用代码：

gridOrderOldState = Newtonsoft.Json.JsonConvert.DeserializeObject(Of futureStateForGrid)(settingsFromBefore)

BasicSimpleOrder的构造函数如下：

Protected Sub New(ammountOfQuoteCurrencyBeingOrdered As Decimal, priceInBasecoin As Decimal, Base As String, Quote As String, exchangeString As String, isSellingInsteadOfBuying As Boolean, customIdentifier As String)
    _ammountOfQuoteCurrencyBeingOrdered = ammountOfQuoteCurrencyBeingOrdered
    _Base = Base
    _Quote = Quote
    _priceInBasecoin = priceInBasecoin
    _exchangeString = exchangeString
    _isSellingInsteadOfBuying = isSellingInsteadOfBuying
    _customIdentifier = customIdentifier
End Sub

核心问题：反序列化时无法自动调用initializeComplexObjects(exchangeObject As ExchangesClass)——构造函数不能接收ExchangesClass类型参数（因为该类型未被序列化，Json.NET无法生成对应实例），但反序列化完成后需要传入exchangeObject来完成BasicSimpleOrder的复杂成员初始化。

解决方案 #

方案1：反序列化后手动遍历调用初始化方法 #

这是最直接的方案，反序列化完成后，遍历futureStateForGrid中所有BasicSimpleOrder（或其派生类）对象，逐个调用initializeComplexObjects方法，传入对应的exchangeObject。

假设futureStateForGrid包含一个Orders属性（存储所有订单对象），代码示例：

' 先完成反序列化
gridOrderOldState = Newtonsoft.Json.JsonConvert.DeserializeObject(Of futureStateForGrid)(settingsFromBefore)

' 遍历所有订单，调用初始化方法
For Each order In gridOrderOldState.Orders
    If TypeOf order Is BasicSimpleOrder Then
        DirectCast(order, BasicSimpleOrder).initializeComplexObjects(yourExchangeObject)
    End If
Next

如果订单嵌套在更复杂的结构里，只需要调整遍历逻辑，找到所有BasicSimpleOrder派生类实例即可。

方案2：利用Json.NET的OnDeserialized特性延迟初始化 #

如果exchangeObject可以通过已序列化的exchangeString属性获取（比如全局维护一个ExchangesClass的字典，用exchangeString做键），可以在BasicSimpleOrder中添加OnDeserialized标记的方法，在反序列化完成后自动触发初始化：

Imports Newtonsoft.Json

Public Class BasicSimpleOrder
    ' 原有代码...

    <OnDeserialized()>
    Private Sub OnDeserializedMethod(context As StreamingContext)
        ' 假设你有全局的Exchange管理类，能通过exchangeString获取对应的ExchangesClass实例
        Dim exchangeObject = ExchangeManager.GetExchangeByString(_exchangeString)
        initializeComplexObjects(exchangeObject)
    End Sub
End Class

这种方案无需手动遍历，反序列化后会自动执行初始化逻辑，但前提是你能通过exchangeString拿到对应的ExchangesClass实例。

方案3：调整类设计为懒加载模式 #

把_exchangeObject和相关的Market对象改为懒加载，在第一次使用时再初始化，这样反序列化后不用立刻调用初始化方法，用到的时候自动完成：

Public Class BasicSimpleOrder
    Private _exchangeObject As ExchangesClass
    Private _lazyExchange As Lazy(Of ExchangesClass)
    Private _lazyMarket As Lazy(Of MarketClass) ' 假设MarketClass是setMarket的参数类型

    ' 原有构造函数不变，添加懒加载初始化
    Protected Sub New(...)
        ' 原有代码...
        _lazyExchange = New Lazy(Of ExchangesClass)(Function() ExchangeManager.GetExchangeByString(_exchangeString))
        _lazyMarket = New Lazy(Of MarketClass)(Function() 
            Dim exch = _lazyExchange.Value
            If exch Is Nothing Then Return Nothing
            Return CoinClass.MarketBaseQuoted(exch.ExchangeStringName, Base, Quote)
        End Function)
    End Sub

    ' 修改原有属性，用懒加载的实例
    Public ReadOnly Property ExchangeObject As ExchangesClass
        Get
            Return _lazyExchange.Value
        End Get
    End Property

    Public ReadOnly Property Market As MarketClass
        Get
            Return _lazyMarket.Value
        End Get
    End Property

    ' 可以保留原有的initializeComplexObjects方法，作为手动触发的选项
    Public Sub initializeComplexObjects(exchangeObject As ExchangesClass)
        If _exchangeObject Is Nothing Then
            _exchangeObject = exchangeObject
            ' 手动初始化Market
            Dim mark = CoinClass.MarketBaseQuoted(exchangeObject.ExchangeStringName, Base, Quote)
            If mark IsNot Nothing Then
                setMarket(mark)
            End If
        End If
    End Sub
End Class

这种方案彻底解决了反序列化后的初始化问题，对象在第一次被使用时才会加载依赖的复杂类型，无需额外手动操作。

内容的提问来源于stack exchange，提问作者user4951