c# - 将嵌套在动态对象中的 C# 列表中的第一项和最后一项序列化为 JSON

Question

我有一个类需要将任何类型的对象序列化为 JSON。如果对象具有一个或多个列表类型的属性，我想序列化整个对象，但只序列化列表中的第一项和最后一项。

例如，我有下面的代码

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

public class Program
{
    public class Product{
        public Product(string name, int price){
            this.Name = name;
            this.Price = price;
        }
        public string Name {get;set;}
        public int Price {get;set;}
    }

    public class ProductResult{
        public ProductResult(List<Product> products, int code){
            this.Products = products;
            this.Code = code;
        }
        public int Code {get;set;}
        public List<Product> Products {get;set;}    
    }

    public static string DoTheThing(object dynamicObject){
        return JsonConvert.SerializeObject(dynamicObject);
    }

    public static void Main()
    {
        var list = new List<Product>(){new Product("product1",100),new Product("product2",100),new Product("product3",100),new Product("product4",100)};
        var result = new ProductResult(list,0);

        string jsonObj = DoTheThing(result);
        Console.WriteLine(jsonObj);
        // Output {"Code":0,"Products":[{"Name":"product1","Price":100},{"Name":"product2","Price":100},{"Name":"product3","Price":100},{"Name":"product4","Price":100}]}
    }
}

我希望它输出以下内容，我需要它能够处理各种对象类型。

{"Code":0,"Products":[{"Name":"product","Price":100},{"Name":"product","Price":100}]}

我看了一下使用 Custom JsonConverter和 Custom ContractResolver但我不确定如何实现这些。

Answer 1

您可以使用自定义的 JsonConverter 来完成此操作，例如:

public class FirstAndLastListConverter : JsonConverter
{
    // We only care about List<> properties
    public override bool CanConvert(Type objectType) => 
        objectType.IsGenericType && objectType.GetGenericTypeDefinition() == typeof(List<>);

    // We are not deserialising, complete this if you really need to, but I don't see why you would
    public override object ReadJson(JsonReader reader, Type objectType, 
        object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        // Convert the value to an IList
        var elements = value as IList;

        // Start a new array
        writer.WriteStartArray();

        // Serialise the first item
        serializer.Serialize(writer, elements[0]);

        // Serialise the last item
        serializer.Serialize(writer, elements[elements.Count - 1]);

        // End the array
        writer.WriteEndArray();
    }
}

然后像这样使用它:

// A settings object to use our new converter
var settings = new JsonSerializerSettings
{
    Converters = new [] { new FirstAndLastListConverter() }
};

// Use the settings when serialising
var json = JsonConvert.SerializeObject(result, settings);