c#-反序列化IEnumerable应用[DataContract]不起作用
作者：互联网
并不是Json.net的新手,而是尝试了以下简单示例,将其序列化然后反序列化,得到以下错误：
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.Text;
using System.Collections;
namespace Timehunter.Base.ServicesTests
{
/// <summary>
/// Summary description for JsonError
/// </summary>
[TestClass]
public class JsonError
{
[TestMethod]
public void TestMethod1()
{
JsonSerializerSettings serializerSettings = new JsonSerializerSettings()
{
DateFormatHandling = DateFormatHandling.IsoDateFormat,
DateParseHandling = Newtonsoft.Json.DateParseHandling.DateTimeOffset
};
Act.Activities acts = new Act.Activities();
acts.Add(new Act.Activity() { Id = 1, Name = "test1" });
acts.Add(new Act.Activity() { Id = 2, Name = "test2" });
string json = Newtonsoft.Json.JsonConvert.SerializeObject(acts, serializerSettings);
Timehunter.Base.Act.Activities target = Newtonsoft.Json.JsonConvert.DeserializeObject<Timehunter.Base.Act.Activities>(json, serializerSettings);
Assert.AreEqual("test1", target.List[0].Name, "Name of first activity");
}
}
}
namespace Timehunter.Base
{
[DataContract]
public class Activity
{
private int _id;
private string _name;
[DataMember]
public int Id
{
get { return this._id; }
set { this._id = value; }
}
[DataMember]
public string Name
{
get { return this._name; }
set { this._name = value; }
}
public Activity()
{
this._id = new int();
this._name = string.Empty;
}
}
[DataContract]
public class Activities : IEnumerable<Activity>
{
private List<Activity> _list;
[DataMember]
public List<Activity> List
{
get { return this._list; }
set { this._list = value; }
}
public Activities()
{
this._list = new List<Activity>();
}
public void Add(Activity item)
{ this._list.Add(item); }
public bool Remove(Activity item)
{ return this._list.Remove(item); }
public int Count()
{ return this._list.Count; }
public IEnumerator<Activity> GetEnumerator()
{
return this._list.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
}
然后我得到以下错误：
Test Name: TestMethod1
Test FullName: Timehunter.Base.ServicesTests.JsonError.TestMethod1
Test Source: C:\Users\hawi.HAWCONS\Documents\Visual Studio 2015\Projects\Timehunter.Data\Timehunter.Base.ServicesTests\JsonError.cs : line 67
Test Outcome: Failed
Test Duration: 0:00:00,2038359
Result StackTrace:
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateNewList(JsonReader reader, JsonArrayContract contract, Boolean& createdFromNonDefaultCreator)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
at Timehunter.Base.ServicesTests.JsonError.TestMethod1() in C:\Users\hawi.HAWCONS\Documents\Visual Studio 2015\Projects\Timehunter.Data\Timehunter.Base.ServicesTests\JsonError.cs:line 79
Result Message:
Test method Timehunter.Base.ServicesTests.JsonError.TestMethod1 threw exception:
Newtonsoft.Json.JsonSerializationException: Cannot create and populate list type Timehunter.Base.Act.Activities. Path '', line 1, position 1.
我究竟做错了什么？
解决方法:
更新2
为了向后兼容,在11.0.2中将其还原.请参阅原始答案以获取解决方案.
更新资料
报告为Issue #1598: DataContractAttribute does not cause JSon object serialization for IEnumerable,已在提交e9e2d00中修复.它应该在10.0.3之后的下一发行版中,它可能是Json.NET版本11.
原始答案
我注意到您已经用[DataContract]和[DataMember]标记了Activity类：
[DataContract]
public class Activities : IEnumerable<Activity>
{
private List<Activity> _list;
[DataMember]
public List<Activity> List
{
get { return this._list; }
set { this._list = value; }
}
// ...
}
应用[DataContact]将导致DataContractJsonSerializer序列化IEnumerable< T>.作为具有属性的JSON对象,而不是作为JSON数组.由于将Json.NET supports data contract attributes应用于非枚举,因此您可能会认为它也会在枚举和集合上尊重它们.
但是,看来这没有实现.如果我使用DataContractJsonSerializer序列化您的类,我会看到
{"List":[{"Id":1,"Name":"test1"},{"Id":2,"Name":"test2"}]}
但是,如果我使用Json.NET进行序列化,则会发现[DataContract]被忽略了：
[{"Id":1,"Name":"test1"},{"Id":2,"Name":"test2"}]
然后,稍后它会在反序列化期间引发异常,因为它不知道如何将成员添加到IEnumerable< Activity>中.类. (如果您的类实现了ICollection< Activity>或had a constructor with an IEnumerable<Activity> argument,则可以添加成员.)
那么,这应该工作吗？文档页面Serialization Attributes指出：
The DataContractAttribute can be used as substitute for JsonObjectAttribute. The DataContractAttribute will default member serialization to opt-in.
这意味着Json.NET应该按照您期望的方式工作.如果需要,可以约report an issue,至少应弄清楚文档.
解决方法是,如果要强制Json.NET将集合序列化为对象,则需要使用[JsonObject]：
[DataContract]
[JsonObject(MemberSerialization = MemberSerialization.OptIn)]
public class Activities : IEnumerable<Activity>
{
private List<Activity> _list;
[DataMember]
[JsonProperty]
public List<Activity> List
{
get { return this._list; }
set { this._list = value; }
}
// Remainder unchanged.
}
如果您有许多应用了[DataContract]的可枚举类,或者无法在模型中添加对Json.NET的依赖性,则可以创建一个custom ContractResolver来检查可枚举类上是否存在[DataContract]并将它们序列化为对象：
public class DataContractForCollectionsResolver : DefaultContractResolver
{
// As of 7.0.1, Json.NET suggests using a static instance for "stateless" contract resolvers, for performance reasons.
// http://www.newtonsoft.com/json/help/html/ContractResolver.htm
// http://www.newtonsoft.com/json/help/html/M_Newtonsoft_Json_Serialization_DefaultContractResolver__ctor_1.htm
// "Use the parameterless constructor and cache instances of the contract resolver within your application for optimal performance."
static DataContractForCollectionsResolver instance;
static DataContractForCollectionsResolver() { instance = new DataContractForCollectionsResolver(); }
public static DataContractForCollectionsResolver Instance { get { return instance; } }
protected DataContractForCollectionsResolver() : base() { }
protected override JsonContract CreateContract(Type objectType)
{
var t = (Nullable.GetUnderlyingType(objectType) ?? objectType);
if (!t.IsPrimitive
&& t != typeof(string)
&& !t.IsArray
&& typeof(IEnumerable).IsAssignableFrom(t)
&& !t.GetCustomAttributes(typeof(JsonContainerAttribute),true).Any())
{
if (t.GetCustomAttributes(typeof(DataContractAttribute),true).Any())
return base.CreateObjectContract(objectType);
}
return base.CreateContract(objectType);
}
}
然后使用以下设置：
var serializerSettings = new JsonSerializerSettings()
{
DateFormatHandling = DateFormatHandling.IsoDateFormat,
DateParseHandling = Newtonsoft.Json.DateParseHandling.DateTimeOffset,
ContractResolver = DataContractForCollectionsResolver.Instance
};
标签：datacontract,json-net,json,c 来源： https://codeday.me/bug/20191027/1943197.html