为什么在尝试通过序列化为 JSON 来打印对象时缺

问题描述

如何在C#中打印任意变量以打印所有成员?

How to print any arbitrary variable in C# so as to print all members?

我用相同的技术找到了三个答案:

I found three answers with the same technique:

• https://stackoverflow.com/a/26181763/2125837 建议使用 Json.NET 进行序列化以及其他答案, 和
• https://tech.io/playgrounds/2098/how-to-dump-objects-in-c/using-json-and-yaml-serializers,
• https:///www.codeproject.com/Articles/1194980/How-to-Dump-Object-for-Debugging-Purposes-in-Cshar

• https://stackoverflow.com/a/26181763/2125837 which suggests serializing with Json.NET among other answers, and
• https://tech.io/playgrounds/2098/how-to-dump-objects-in-c/using-json-and-yaml-serializers,
• https://www.codeproject.com/Articles/1194980/How-to-Dump-Object-for-Debugging-Purposes-in-Cshar

但是，当我尝试使用以下代码时，

However, when I tried it out, with the following code,

using System;
using System.Collections.Generic;

using Newtonsoft.Json;

public static class Program
{
    public static void Main()
    {
        Test t1 = new Test(1, 2);
        {
            string json = JsonConvert.SerializeObject(t1, Formatting.Indented);
            Console.WriteLine(json);
        }
        Dump(t1);

        // Add 3 objects to a List.
        List<Test> list = new List<Test>();
        list.Add(new Test(1, 2));
        list.Add(new Test(3, 4));
        list.Add(new Test(5, 6));

        Console.WriteLine(list.ToString());
        {
            string json = JsonConvert.SerializeObject(list, Formatting.Indented);
            Console.WriteLine(json);
        }
    }

    public class Test
    {
        int A;
        int b;
        public Test(int _a, int _b)
        {
            A = _a;
            b = _b;
        }
    };

    public static void Dump<T>(this T x)
    {
        string json = JsonConvert.SerializeObject(x, Formatting.Indented);
        Console.WriteLine(json);
    }
}

我得到的都是空的 Test 输出:

All that I got are empty Test outputs:

{}
{}
System.Collections.Generic.List`1[Program+Test]
[
  {},
  {},
  {}
]

使用 Json.NET 序列化为 JSON 时，为什么我的所有班级成员都丢失了?

Why are all my class members missing when serializing to JSON with Json.NET?

推荐答案

默认情况下，Json.NET 只会序列化 public 属性和字段.您的字段 A 和 b 是 private.要使 Json.NET 序列化非公共(私有或内部)成员，您可以:

By default Json.NET will only serialize public properties and fields. Your fields A and b are private. To cause nonpublic (private or internal) members to be serialized by Json.NET, you can:

1. 公开:

public int A;
public int b;

但是，从风格上讲，如果您要将它们公开，最好将它们转换为属性:

However, stylistically, if you are going to make them be public, it's better to convert them to properties:

public class Test
{
    public int A { get; private set; }
    public int b { get; private set; }
    public Test(int a, int b)
    {
        this.A = a;
        this.b = b;
    }
};

只有 getter 需要公开，Json.NET 才能序列化它们.

Only the getters need be public for Json.NET to serialize them.

然后用 [JsonProperty] 标记:

[JsonProperty]
int A;
[JsonProperty]
int b;

这也适用于非公共财产.

This works for nonpublic properties as well.

用 [DataContract] 和您的字段与 [数据成员]:

[DataContract]
public class Test
{
    [DataMember]
    int A;
    [DataMember]
    int b;
    public Test(int _a, int _b)
    {
        A = _a;
        b = _b;
    }
};

[JsonObject(MemberSerialization = MemberSerialization.Fields)]
public class Test
{
    // Remainder as before...
};

var settings = new JsonSerializerSettings
{
    ContractResolver = DeclaredFieldContractResolver.Instance
};
var json = JsonConvert.SerializeObject(t1, Formatting.Indented, settings);

public class Test
{
    public class TestJsonConverter : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return typeof(Test).IsAssignableFrom(objectType);
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            var test = (Test)value;

            writer.WriteStartObject();
            writer.WritePropertyName(nameof(Test.A));
            serializer.Serialize(writer, test.A);
            writer.WritePropertyName(nameof(Test.b));
            serializer.Serialize(writer, test.b);
            writer.WriteEndObject();
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }
    }
    // Remainder as before
}

var json = JsonConvert.SerializeObject(t1, Formatting.Indented, new Test.TestJsonConverter());