使用ApiController獲取List時出現System.InvalidOperationException

Question

當我在我的應用程序中訪問/WeedAPI/ URL時，出現以下錯誤。我如何讓我的web API工作？ （控制器，型號代碼遵循）

完整的錯誤細節：

<Error> 
    <Message>An error has occurred.</Message> 
    <ExceptionMessage> 
     The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'. 
    </ExceptionMessage> 
    <ExceptionType>System.InvalidOperationException</ExceptionType> 
    <StackTrace/> 
    <InnerException> 
     <Message>An error has occurred.</Message> 
     <ExceptionMessage> 
      Type 'WeedCards.Models.Weed' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types. 
     </ExceptionMessage> 
     <ExceptionType> 
      System.Runtime.Serialization.InvalidDataContractException 
     </ExceptionType> 
     <StackTrace> 
      at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.ThrowInvalidDataContractException(String message, Type type) at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type) at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type) at System.Runtime.Serialization.XmlObjectSerializerContext.GetDataContract(Int32 id, RuntimeTypeHandle typeHandle) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) at WriteArrayOfWeedToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract) at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiTypeAtTopLevel(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle originalDeclaredTypeHandle, Type graphType) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.WriteObject(XmlWriter writer, Object graph) at System.Net.Http.Formatting.XmlMediaTypeFormatter.<>c__DisplayClass7.<WriteToStreamAsync>b__6() at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token) 
     </StackTrace> 
    </InnerException> 
</Error> 

我ApiController的子類：

public class WeedAPIController : ApiController 
{ 
    // 
    // GET: /WeedAPI/ 

    public IEnumerable<Weed> GetAllWeeds() 
    { 
     return WeedData.GetWeeds(); 
    } 

} 

我的數據：

public class WeedData 
{ 
    public static Dictionary<string,WeedFamily> GetFamilies(){ 
     return new Dictionary<string,WeedFamily> 
     { 
      {"mustard",new WeedFamily("Mustard","Brassicaceae")} 
      ,{"pigweed",new WeedFamily("Pigweed","Amaranthus")} 
      ,{"sunflower",new WeedFamily("Sunflower","Asteraceae")} 
     }; 
    } 

    public static List<Weed> GetWeeds(){ 
     var Families = GetFamilies(); 
     return new List<Weed> 
     { 
      new Weed("Hairy Bittercress","Cardamine hirsuta",Families["mustard"]) 
      ,new Weed("Little Bittercress","Cardamine oligosperma",Families["mustard"]) 
      ,new Weed("Shepherd's-Purse","Capsella bursa-pastoris",Families["mustard"]) 
      ,new Weed("Wild Mustard","Sinapis arvensis/Brassica kaber",Families["mustard"]) 
      ,new Weed("Wild Radish","Raphanus raphanistrum",Families["mustard"]) 
      ,new Weed("Radish","Raphanus sativus",Families["mustard"]) 
      ,new Weed("Redroot Pigweed","Amaranthus retroflexus",Families["pigweed"]) 
      ,new Weed("Prickly Lettuce","Lactuca serriola",Families["sunflower"]) 
      ,new Weed("Spiny Sowthistle","Sonchus asper",Families["sunflower"]) 
      ,new Weed("Annual Sowthistle","Sonchus oleraceus",Families["sunflower"]) 

     }; 
    } 
} 

Answer 1

答案是在例外。用[DataContract]標記Weed類，以便它可以被DataContractSerializer序列化。