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我有一个对象，其中包含一个名为 Email 的属性，该属性的类型为System.Net.Mail.MailAddress。我能够序列化我的对象JSON.Net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：

找不到用于类型的构造函数System.Net.Mail.MailAddress。一个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标有 JsonConstructor 属性的构造函数。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，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 成功反序列化这个属性。

更新

让我详细说明一下对象的外观以及我尝试过的内容。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
  }
}

在我的联系课程中，我有这样的事情：

<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

然后我删除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

通过使用该属性并将转换器添加到序列化程序，一旦序列化程序命中 Email 属性，它将正确创建一个邮件对象，但它之后的任何属性都不会正确反序列化。

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1 回答 1

0

我认为问题在于您的ReadJson方法在完成时使阅读器位置不正确，从而弄乱了反序列化过程的其余部分。

将阅读器想象成 JSON 数据的只进游标。当 ReadJson 被调用时，它被定位为即将读取转换器说它可以处理的下一个项目。在你的情况下EmailConverter，它将被定位为即将读取 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，因此它需要使用该对象的所有JSON。我认为正在发生的事情是读者没有进入右括号。您可能可以通过在提取Address值后继续进一步阅读来修复它，注意不要超出Email对象的末尾，但这种方法容易出错。一个更好的主意是使用 JSON.Net 的内置 LINQ-to-JSON 工具，让您可以轻松地将整个Email对象作为一个块读取，然后从中挑选出您需要的部分。这将使阅读器正确定位以进行其余的反序列化，然后您不必担心。它还大大简化了代码。

这是我将如何编写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
于 2013-09-02T08:45:14.533 回答