数组的Json DeSerialization到IEnumerable失败

Question

cs具有下列属性：

 public CustomerExtensions CustomerExtensions { get; set; }

CustomerExtensions类：

[DefaultMember("Item")]
public class CustomerExtensions  : 
     IEnumerable<CustomerExtension>, IEnumerable, IEnumerator
{
       public CustomerExtensions();
       public CustomerExtensions(List<CustomerExtension> customerExtensions);
}

CustomerExtension类：

public class CustomerExtension 
{
    public CustomerExtension();
    
    public int CustomerId { get; set; }       
    public int CustomerType { get; set; }       
}

所以当我把json流写成这样：

result = JsonConvert.DeserializeObject<Customer>(response, custDefualtSettings());

响应：

{
    "$id": "1",
    "$type": "Common.Customer, PublicKeyToken=f291d5e4",
    "CashPrice": 47042.74,
    "AmountFinanced": 47042.74, 
    "CustomerExtensions": {
        "$id": "4",
        "$type": "System.Collections.Generic.List`1[[Common.CustomerExtension, PublicKeyToken=f291d5e4]], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=f291d5e4",
        "$values": [
            {
                "$id": "5",
                "$type": "Common.CustomerExtension, PublicKeyToken=f291d5e4",
                "CustomerId": 11946,
                "CustomerType": 1,                             
            },
            {
                "$id": "5",
                "$type": "Common.CustomerExtension, PublicKeyToken=f291d5e4",
                "CustomerId": 11046,
                "CustomerType": 3,                             
            }        
        ]
    }

反序列化失败，有以下错误：

无法创建和填充列表类型Common.CustomerExtensions。路径'CustomerExtensions.$values'，第1行，位置2725。

有人能指出正确的方向吗..？

答案：

using Newtonsoft.Json;
using System;
using System.Collections.Generic;

public class CustomerExtensionsConverter : JsonConverter<CustomerExtensions>
{
    public override bool CanWrite => false;

    public override CustomerExtensions ReadJson(JsonReader reader, Type objectType, CustomerExtensions existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        var list = serializer.Deserialize<List<CustomerExtension>>(reader);
        return new CustomerExtensions(list);
    }

    public override void WriteJson(JsonWriter writer, CustomerExtensions value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Answer 1

CustomerExtensions实现IEnumerable<CustomerExtension>，因此反序列化器在默认情况下将期望它从json数组序列化和反序列化。它将尝试创建一个新实例，然后调用Add(CustomerExtension item)来填充它。但是，您没有实现IList，因此没有可以使用的Add()方法，而且它也不知道该做什么。

为什么您需要一个自定义类来处理这个问题？在您的类中没有额外的逻辑，有public List<CustomerExtension> CustomerExtensions { get; set; }就足够了吗？

编辑

由于无法更改类定义，因此可以创建自定义JsonConverter：

using Newtonsoft.Json;
using System;
using System.Collections.Generic;

public class CustomerExtensionsConverter : JsonConverter<CustomerExtensions>
{
    public override bool CanWrite => false;

    public override CustomerExtensions ReadJson(JsonReader reader, Type objectType, CustomerExtensions existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        var list = serializer.Deserialize<List<CustomerExtension>>(reader);
        return new CustomerExtensions(list);
    }

    public override void WriteJson(JsonWriter writer, CustomerExtensions value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

若要使用转换器，请在调用JsonSerializerSettings时将其添加到Deserialize对象中。

var settings = custDefualtSettings();
settings.Converters.Add(new CustomerExtensionsConverter());
result = JsonConvert.DeserializeObject<Customer>(response, settings);

我还没有对此进行测试，但它应该会让您对实现的样子有一个大致的了解。