序列化特定类型时，如何使JSON.Net序列化程序调用ToString()? [英] How to make JSON.Net serializer to call ToString() when serializing a particular type?

问题描述

我正在使用Newtonsoft.Json序列化程序将C#类转换为JSON.对于某些类，我不需要将序列化器设置为具有单个属性的实例，而只需在对象上调用ToString，即

I am using Newtonsoft.Json serializer to convert C# classes to JSON. For some classes I don't need the serializer to an instance to individual properties, but instead just call ToString on the object, i.e.

public class Person
{
   public string FirstName { get; set; }
   public string LastName { get; set; }

   public override string ToString() { return string.Format("{0} {1}", FirstName, LastName ); }
}

我应该怎么做才能将Person对象作为其ToString()方法的结果进行序列化?我可能有很多这样的类，所以我不想以特定于Person类的序列化器结尾，我想拥有一个可以应用于任何类的序列化器(我想通过属性).

What should I do to get the Person object serialized as the result of its ToString() method? I may have many classes like this, so I don't want to end up with a serializer specific for Person class, I want to have one than can be applicable to any classe (via attribute I guess).

推荐答案

您可以使用自定义的 JsonConverter :

You can do this easily with a custom JsonConverter:

public class ToStringJsonConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return true;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteValue(value.ToString());
    }

    public override bool CanRead
    {
        get { return false; }
    }

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

要使用转换器，请使用以下[JsonConverter]属性来装饰需要序列化为字符串的所有类:

To use the converter, decorate any classes that need to be serialized as string with a [JsonConverter] attribute like this:

[JsonConverter(typeof(ToStringJsonConverter))]
public class Person
{
    ...
}

以下是演示转换器运行的演示:

Here is a demo showing the converter in action:

class Program
{
    static void Main(string[] args)
    {
        Company company = new Company
        {
            CompanyName = "Initrode",
            Boss = new Person { FirstName = "Head", LastName = "Honcho" },
            Employees = new List<Person>
            {
                new Person { FirstName = "Joe", LastName = "Schmoe" },
                new Person { FirstName = "John", LastName = "Doe" }
            }
        };

        string json = JsonConvert.SerializeObject(company, Formatting.Indented);
        Console.WriteLine(json);
    }
}

public class Company
{
    public string CompanyName { get; set; }
    public Person Boss { get; set; }
    public List<Person> Employees { get; set; }
}

[JsonConverter(typeof(ToStringJsonConverter))]
public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public override string ToString() 
    { 
        return string.Format("{0} {1}", FirstName, LastName); 
    }
}

输出:

{
  "CompanyName": "Initrode",
  "Boss": "Head Honcho",
  "Employees": [
    "Joe Schmoe",
    "John Doe"
  ]
}

---

如果还需要能够从字符串转换回对象，则可以在转换器上实现ReadJson方法，以便它寻找并调用public static Parse(string)方法.注意:请确保将转换器的CanRead方法更改为返回true(或完全删除CanRead重载)，否则将永远不会调用ReadJson.

---

If you also need to be able to convert from string back to an object, you can implement the ReadJson method on the converter such that it looks for a public static Parse(string) method and calls it. Note: be sure to change the converter's CanRead method to return true (or just delete the CanRead overload altogether), otherwise ReadJson will never be called.

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    MethodInfo parse = objectType.GetMethod("Parse", new Type[] { typeof(string) });
    if (parse != null && parse.IsStatic && parse.ReturnType == objectType)
    {
        return parse.Invoke(null, new object[] { (string)reader.Value });
    }

    throw new JsonException(string.Format(
        "The {0} type does not have a public static Parse(string) method that returns a {0}.", 
        objectType.Name));
}

当然，要使上述方法起作用，还需要确保在要转换的每个类上实现合适的Parse方法(如果尚不存在).对于上面显示的示例Person类，该方法可能看起来像这样:

Of course, for the above to work, you will also need to make sure to implement a suitable Parse method on each class you're converting, if it doesn't already exist. For our example Person class shown above, that method might look something like this:

public static Person Parse(string s)
{
    if (string.IsNullOrWhiteSpace(s))
        throw new ArgumentException("s cannot be null or empty", "s");

    string[] parts = s.Split(new char[] { ' ' }, 2);
    Person p = new Person { FirstName = parts[0] };
    if (parts.Length > 1)
        p.LastName = parts[1];

    return p;
}

往返演示: https://dotnetfiddle.net/fd4EG4

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