无法转换 System.Collections.Generic.IEnumerable 类型的对象 - Web API 问题

Question

所以我正在尝试在 VS2015 中使用 VB 创建一个简单的网络 API 2。然而，我确实开始工作的代码 只有 returns 一个简单的字符串 ，其中 Web Api 需要序列化数据 所以 XML 或 JSON 可以返回。

'Here I initialize and populate my object       
Public widgetObj As New widgetModelClass("bottle", 1)


' Below kind of works, but simply returns a string **instead** of 
' the serialized data for XML or JSON the Web API should return. 
' it returns: {"Name":"bottle","ID":1}
 Public Function GetValues() As widgetModelClass
     Return widgetObj 
 End Function

下面的代码失败除了：

Unable to cast object of type System.Collections.Generic.IEnumerable

Public Function GetValues() As IEnumerable(Of widgetModelClass)
    Return widgetObj
End Function

我定义了我的模型class如下

Public Class widgetModelClass
    Public Sub New(ByVal name As String, ByVal id As Integer)
        Me.Name = name
        Me.ID = id
    End Sub

    Private m_Name As String
    Public Property Name() As String
        Get
            Return m_Name
        End Get
        Set
            m_Name = Value
        End Set
    End Property

    Private m_ID As Integer
    Public Property ID() As Integer
        Get
            Return m_ID
        End Get
        Set
            m_ID = Value
        End Set
    End Property
End Class

完整的错误信息:

An error has occurred.Unable to cast object of type 'TestApp.widgetModelClass' to type 'System.Collections.Generic.IEnumerable1[TestApp.widgetModelClass]'.</ExceptionMessage><ExceptionType>System.InvalidCastException</ExceptionType><StackTrace> at lambda_method(Closure , Object , Object[] ) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments) at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary2 arguments, CancellationToken cancellationToken) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ApiControllerActionInvoker.d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ActionFilterResult.d__2.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()

Answer 1

在你的样本中你 return widgetObj 但它不是你想要的 IEnumerable(Of widgetModelClass) 的实例。

您必须将声明更改为 return widgetModelClass 的一个实例：

Public Function GetValues() As widgetModelClass
    Return widgetObj
End Function

或您的 return 声明 return IEnumerable(Of widgetModelClass):

Public Function GetValues() As IEnumerable(Of widgetModelClass)
    Return New List(Of widgetModelClass)(New widgetModelClass() { widgetObj } )
End Function

无法转换 System.Collections.Generic.IEnumerable 类型的对象 - Web API 问题

Unable to cast object of type System.Collections.Generic.IEnumerable - Web API issue

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ienumerable

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