施法错误wcf

Question

我无法施放我的物体。我得到：“无法投射'ClassA'类型的对象来键入'ClassB'”。

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 

而我三类：

<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 

JSON对象我送：

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

每次我寄这封信给我收到以下错误铸造服务器：

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'. 

能有人帮我，我不知道我做错了吗？

Answer 1

ClassC是ClassB的列表，因此它试图将ClassA强制转换为ClassB。

ClassB继承ClassA，因此ClassB具有ClassA所需的所有信息。但ClassA没有ClassB中的所有信息，因此投射失败。