wcf 转换错误

Question

我无法投射我的物体。我得到：“无法将‘ClassA’类型的对象转换为‘ClassB’类型”。

服务类：

 Public Class svc_Insp

    Implements Isvc_Insp

    Public Function Test(ByVal pm_income As ClassC) As String Implements Isvc_Insp.Test
    Dim lv_retVal As String
    Try

       For Each item As Object In pm_income.Items
        Try
        Logger.Log(item)
        Dim lv_Item As ClassB= CType(item, ClassB)
        Catch ex As Exception
        Logger.Log(ex.Message)
        lv_retVal = ex.Message
        End Try
       Next

    Catch ex As Exception
       lv_retVal = ex.Message
    End Try

    Return lv_retVal
    End Function Logger.Log(ex) 
    End Class

接口：

<ServiceContract()> _
Public Interface Isvc_Insp
  <OperationContract()> _

 <WebInvoke(Method:="POST", BodyStyle:=WebMessageBodyStyle.Bare, RequestFormat:=WebMessageFormat.Json, ResponseFormat:=WebMessageFormat.Json, UriTemplate:="Test")> _

 Function Test(ByVal pm_c As ClassC) As String
End Interface

我的三个类：

<DataContract(), KnownType(GetType(ClassB)), KnownType(GetType(ClassC)), KnownType(GetType(List(Of ClassA)))> _

Public Class ClassA
 Private _Name As String
 <DataMember()> _
 Public Property Name () As String
  Get
   Return _Name 
  End Get
  Set(ByVal value As String)
   _Name = value
  End Set
 End Property

 Private _Age As Integer
 <DataMember()> _
 Public Property Age () As Integer
  Get
   Return _Age 
  End Get
  Set(ByVal value As Integer)
   _Age = value
  End Set
 End Property
End Class

<DataContract()> _
Public Class ClassB
 Inherits ClassA
 Private _LastName As String
 <DataMember()> _
 Public Property LastName () As String
  Get
   Return _LastName 
  End Get
  Set(ByVal value As String)
   _LastName = value
  End Set
 End Property
End Class

<DataContract()> _
Public Class ClassC
 Private _Items As List(Of ClassA)
 <DataMember()> _
 Public Property Items() As List(Of ClassA)
  Get
   Return _Items
  End Get
  Set(ByVal value As List(Of ClassA))
   _Items = value
  End Set
 End Property
End Class

我发送的 json 对象：

{ 
 "Items": [  {
   "__type": "ClassB:#",
   "LastName": "Power",
   "Name": "David",   
   "Age": "30"
  },
  {
   "__type": "ClassA:#",
   "Name": "Dave",
   "Age": "20"
  },
  {
   "__type": "ClassB:#",
   "LastName": "Bullet",
   "Name": "Chris",
   "Age": "40"
  }
 ]
}

每次我将此发送到服务器我收到以下转换错误：

24-05-2011 16:36:57 - Unable to cast object of type 'ClassA' to type 'ClassB'.
24-05-2011 16:36:57 - ClassA
24-05-2011 16:36:57 - Unable to cast object of type 'ClassA' to type 'ClassB'.
24-05-2011 16:36:57 - ClassA
24-05-2011 16:36:57 - Unable to cast object of type 'ClassA' to type 'ClassB'.

有人可以帮助我吗？我不知道我做错了什么？

Answer 1

ClassC 是 ClassB 的列表，这就是它尝试将 ClassA 转换为 ClassB 的原因。

ClassB继承了ClassA，因此ClassB拥有ClassA所需的所有信息。但是 ClassA 没有 ClassB 中的所有信息，因此转换失败。