Question

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

无法找到用于类型System.Net.Mail.MailAddress的构造函数。一个类应该有一个默认的构造函数，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没有默认构造函数，这就是我收到此错误的原因。我的问题是，如果没有转换属性类型，有没有办法解决这个问题？我看到有自定义转换器，但我没有运气让JSON.Net成功反序列化这个属性。

更新

让我详细说明对象的外观和我尝试过的内容。该对象看起来像这样：

{
  "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": "jamesdean890@fake.com.au"
    },
    "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
  }
}

在我的联系课上，我有类似的东西：

<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

然后我找到了一个像这样的转换器：

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

通过使用属性并将转换器添加到序列化程序，一旦序列化程序点击Email属性，它就会正确创建一个邮件对象，但之后的任何属性都不能正确反序列化。

Answer 1

我认为问题是你的ReadJson方法在读者完成时会使读者错误定位，从而弄乱了反序列化过程的其余部分。

将读者视为JSON数据的仅向前游标。调用ReadJson时，它的位置使得它即将读取转换器说它可以处理的下一个项目。对于EmailConverter，它的位置即将阅读JSON的这一部分：

{
  "DisplayName": "",
  "User": "jamesdean890",
  "Host": "fake.com.au",
  "Address": "jamesdean890@fake.com.au"
}

由于转换器应该处理整个Email对象，因此需要使用 all 该对象的JSON。我认为正在发生的事情是读者没有进入最后阶段。您可以通过在提取Address值之后继续阅读更多来修复它，注意不要超出Email对象的末尾，但这种方法容易出错。更好的想法是使用JSON.Net的内置LINQ-to-JSON工具，允许您轻松地将整个Email对象作为块读取，然后从中挑选出您需要的部分。这将使读者正确地定位其余的反序列化，然后您不必担心它。它还大大简化了代码。

以下是我写EmailConverter：

的方法

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

JSON.Net反序列化MailAddress

1 个答案: