Question

我有以下代码从web api服务获取对象。

在以下代码行

response.Content.ReadAsAsync<CMLandingPage>().Result;

我得到以下异常：

InnerException = {"Could not create an instance of type MLSReports.Models.IMetaData. Type is an interface or abstract class and cannot be instantiated. Path 'BaBrInfo.Series[0].name', line 1, position 262."}

非常感谢任何指针。

 CMLandingPage lpInfo = new CMLandingPage();

            try
            {
                using (HttpClient client = new HttpClient())
                {
                    // Add an Accept header for JSON format
                    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                    response = client.PostAsJsonAsync(LPChartinfoapiURL, criteria.Mlsnums).Result;
                }
                // Throw exception if not a success code.
                response.EnsureSuccessStatusCode();
                // Parse the response body.
                lpInfo = response.Content.ReadAsAsync<CMLandingPage>().Result;
                }

CMLandingPage：

namespace MLSReports.Models
{
    public class CMLandingPage
    {
        public CMLandingPage()  {  }

        public CMColumn BaBrInfo { get; set; }

     }
  public class CMColumnItem<T> : IMetaData
    {
        #region Constructors and Methods
        public CMColumnItem()   {   }
        #endregion

        #region Properties and Fields
        public string name { get; set; }
        public List<T> data { get; set; }
        public string color { get; set; }
        #endregion

    }

    public class CMColumn
    {
        #region Constructor and Method
        public CMColumn()
        {
           Series = new List<IMetaData>();
        }
        #endregion

        #region Properties and Fields
        public string ChartType { get; set; }
        public string ChartTitle { get; set; }
        public List<IMetaData> Series { get; set; }
        #endregion    
    }
}

Answer 1

您的CmColumn班级上有此属性：

    public List<IMetaData> Series { get; set; }

WebApi控制器显然正在尝试根据您发送它的参数值构造一个对象。当它到达名为“BaBrInfo.Series [0] .name”的值时，它知道它应该创建一个新的IMetaData对象，以便它可以设置它的name并将其添加到{ {1}}属性，但Series只是一个接口：它不知道要构造什么类型的对象。

尝试将IMetaData更改为实现该接口的某种具体类型。

Answer 2

您需要让序列化程序在json有效负载和反序列化器中包含类型以使用包含的类型：

//Serialization
var config = new HttpConfiguration();
config.Formatters.JsonFormatter.SerializerSettings.TypeNameHandling = TypeNameHandling.Auto;
return Request.CreateResponse(HttpStatusCode.OK, dto, config);

//Deserialization
var formatter = new JsonMediaTypeFormatter
{
    SerializerSettings = { TypeNameHandling = TypeNameHandling.Auto }
};
response.Content.ReadAsAsync<CMLandingPage>(new [] { formatter }).Result;

POLYMORPHIC SERIALIZATION USING NEWTON JSON.NET IN HTTPCONTENT

ReadAsAsync - 错误：“Type是一个接口或抽象类，无法实例化。”

2 个答案: