JSON.Net反序列化邮件地址

Question

我有一个对象，它包含一个名为Email的属性，类型为System.Net.Mail.MailAddress。我能够用JSON.Net序列化我的对象并将其存储在数据库中。但是，我无法成功地反序列化我的对象。我得到的错误信息是：

找不到用于类型System.Net.Mail.MailAddress的构造函数。类应该有一个默认构造函数、一个带参数的构造函数或一个用JsonConstructor属性标记的构造函数。路径"Item1.Email.DisplayName".

我知道MailAddress没有默认的构造函数，这就是我收到这个错误的原因。我的问题是，有没有办法在不转换属性类型的情况下解决这个问题？我看到有自定义转换器，但我没有任何运气让JSON.Net成功地反序列化这一属性。

更新

让我详细说明一下这个物体是什么样子的，以及我尝试过什么。对象看起来像这样：

{
  "Item1": {
    "ReceiveNewsletter": false,
    "HomePhone": "074567 8901",
    "SpouseTitle": null,
    "SpouseFirstName": null,
    "SpouseLastName": null,
    "Address": {
      "StreetAddress1": "123 Fake Street",
      "StreetAddress2": null,
      "City": null,
      "State": "QLD",
      "PostalCode": "4627",
      "Suburb": "Abercorn",
      "AustralianAddress": true
    },
    "CustomerAddresses": [],
    "ID": -1,
    "Title": "",
    "FirstName": "James",
    "LastName": "Dean",
    "DisplayName": "James Dean",
    "Email": {
      "DisplayName": "",
      "User": "jamesdean890",
      "Host": "fake.com.au",
      "Address": "[e-mail]"
    },
    "WorkPhone": null,
    "OtherPhone": "",
    "CellPhone": "0423 456 789",
    "Notes": null
  },
  "Item2": {
    "ID": -1,
    "CustomerID": -1,
    "Pet": {
      "ID": -1,
      "Name": "Fae",
      "Breed": "Puppy Dog",
      "DateOfDeath": "2013-08-28T00:00:00-05:00",
      "ServiceDate": "2013-08-28T00:00:00-05:00",
      "ContactDate": "0001-01-01T00:00:00-06:00",
      "PetGender": 1,
      "ReferralClinicID": 462,
      "ReferralPaidDate": null,
      "Row": "u0000",
      "Plot": -1,
      "CollectedBy": null,
      "DeliverDate": "0001-01-01T00:00:00-06:00",
      "DeliveredBy": null,
      "Customer": null,
      "RenewDate": null
    },
    "Service": {
      "ID": -1,
      "Quantity": 1,
      "Price": 285.0,
      "ProductName": "Cremation",
      "ProductID": 1,
      "LineItemState": 0,
      "Plaque": null,
      "IsPlaque": false,
      "Void": false
    },
    "LineItems": [],
    "Notes": "",
    "EnteredBy": null,
    "IsRenewal": false,
    "IsLocked": false,
    "CreateDate": "0001-01-01T00:00:00-06:00",
    "OrderTotal": 285.0
  }
}

在我的联系人课程中，我有这样的东西：

<JsonConverter(GetType(EmailConverter))>
Public Property Email() As Net.Mail.MailAddress
    Get
        Return _Email
    End Get
    Set(ByVal value As Net.Mail.MailAddress)
        _Email = value
    End Set
End Property

然后，我发现了一个类似这样的转换器：

Public Class EmailConverter
    Inherits JsonConverter
    Public Overrides Function ReadJson(reader As JsonReader, objectType As Type, existingValue As Object, serializer As JsonSerializer) As Object
        Dim mailAddress As System.Net.Mail.MailAddress = Nothing
        If objectType = GetType(System.Net.Mail.MailAddress) Then
            While reader.Path <> "Item1.Email.Address"
                reader.Read()
            End While
            reader.Read()
            mailAddress = New Net.Mail.MailAddress(reader.Value.ToString)
        End If
        Return mailAddress
    End Function
    Public Overrides Function CanConvert(objectType As Type) As Boolean
         Return objectType = GetType(System.Net.Mail.MailAddress)
    End Function
    Public Overrides Sub WriteJson(writer As JsonWriter, value As Object, serializer As JsonSerializer)
    End Sub
End Class

通过使用该属性并将转换器添加到序列化程序，只要序列化程序达到Email属性，它就会正确创建邮件对象，但之后的任何属性都不会正确反序列化。

Answer 1

我认为问题在于ReadJson方法在完成时使读取器的位置不正确，从而打乱了反序列化过程的其余部分。

将读取器视为JSON数据的仅向前的游标。当ReadJson被调用时，它的位置使得它即将读取转换器所说的它可以处理的下一个项目。在您的EmailConverter的情况下，它的位置将刚好读取JSON:的这一部分

{
  "DisplayName": "",
  "User": "jamesdean890",
  "Host": "fake.com.au",
  "Address": "[e-mail]"
}

由于转换器应该处理整个Email对象，因此它需要消耗该对象的所有JSON。我认为现在的情况是读者没有进入最后阶段。您可能可以通过在提取Address值后继续进一步读取来修复它，注意不要超出Email对象的末尾，但这种方法很容易出错。一个更好的想法是使用JSON.Net内置的LINQ到JSON功能，使您可以轻松地将整个Email对象作为一个块读取，然后从中只挑选出您需要的部分。这将使读取器在反序列化的其余部分处于正确的位置，然后您就不必担心了。它还大大简化了代码。

以下是我如何编写EmailConverter:

Imports System.Net.Mail
Imports Newtonsoft.Json
Imports Newtonsoft.Json.Linq
Public Class EmailConverter
    Inherits JsonConverter
    Public Overrides Function CanConvert(objectType As Type) As Boolean
        Return objectType = GetType(MailAddress)
    End Function
    Public Overrides Function ReadJson(reader As JsonReader, objectType As Type, existingValue As Object, serializer As JsonSerializer) As Object
        Dim jsonObject As JObject = JObject.Load(reader)
        Dim address As String = jsonObject("Address").Value(Of String)()
        Dim mailAddress As MailAddress = New MailAddress(address)
        Return mailAddress
    End Function
    Public Overrides Sub WriteJson(writer As JsonWriter, value As Object, serializer As JsonSerializer)
        serializer.Serialize(writer, value)
    End Sub
End Class