C＃JSON反序列化：我可以拦截反序列化和选择更改的结果？ [英] C# JSON deserialization: can I intercept the deserialization and optionally change the result?

问题描述

我们已经有了一些JSON，我们反序列化到C＃中的强类型的对象图。但是，我们有一个问题：有时会出现在该映射到我们的模型一个布尔值的属性的JSON（例如，空字符串）一个空值

We've got some JSON that we are deserializing into a strongly-typed object graph in C#. However, we've got one issue: sometimes there is an "empty" value in the JSON (e.g., empty string) in a property that maps to a boolean value in our model.

在我们的例子中，我们知道，100％的时间，我们可以把这些空白值布尔假。

In our case, we know that 100% of the time, we can translate these "blank" values to Boolean false.

不过，我已经试过了JSON解串器不知道这个（可以理解）。

However, the JSON deserializers I've tried don't know about this (understandably).

我一直试图找到一种方法拦截每个属性的反序列化，以及可选改写输出。也就是说，如果有一个拦截器的方法我可以注册，这是这样的：

I've been trying to find a way to intercept the deserialization of each property, and optionally override the output. I.e., if there was an "interceptor" method I could register, that looked like this:

    public Boolean JsonDeserializationInterceptor(String rawJson, System.Type targetType, out object result)
    {
        Boolean overrodeValue = false;
        result = null;
        if(targetType == typeof(System.Boolean))
        {
            overrodeValue = true;
            // We'll pretend that we're interpreting the string "Yes" as
            // true, and all other values are false.
            if (rawJson != null && rawJson.ToLower() == "\"yes\"")
                result = true;
            else
                result = false;
        }

        return overrodeValue;
    }

这只是假设，当然，但我希望它给你的想法是什么我试图完成的任务。

That's just hypothetical, of course, but hopefully it gives you an idea of what I'm trying to accomplish.

在我的研究，我一直没能想出一个办法做到这一点。我看着 Json.NET ，的 System.Runtime.Serialization.Json.DataContractJsonSerializer 和的System.Web.Script.Serialization.JavaScriptSerializer 。我敢打赌，有一种方法可以做到这一点，我只是一直没能弄明白。

In my research I have not been able to figure out a way to do this. I've looked at Json.NET, System.Runtime.Serialization.Json.DataContractJsonSerializer, and System.Web.Script.Serialization.JavaScriptSerializer. I bet there is a way to do this, and I just haven't been able to figure it out.

修改：我想你也许能够使用的 JsonConverterAttribute ，但到目前为止，我还没有能够得到那个工作。

Edit: I think you might be able to use the JsonConverterAttribute, but so far I have not been able to get that working.

推荐答案

编写自定义 JsonConverter 为基本类型是非常straghtforward：

Writing a custom JsonConverter for a primitive type is pretty straghtforward:

using System;
using Newtonsoft.Json;

namespace So16972364JsonDeserializeConverter
{
    class BoolConverter : JsonConverter
    {
        public override void WriteJson (JsonWriter writer, object value, JsonSerializer serializer)
        {
            serializer.Serialize(writer, value);
        }

        public override object ReadJson (JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            switch (reader.TokenType) {
                case JsonToken.String:
                    if ((string)reader.Value == "")
                        return false;
                    break;
                case JsonToken.Boolean:
                    return reader.Value;
            }
            throw new JsonReaderException("Expected boolean or empty string.");
        }

        public override bool CanConvert (Type objectType)
        {
            return objectType == typeof(bool);
        }
    }

    class Program
    {
        const string json = @"
{
    b1: true,
    b2: false,
    b3: ''
}
";

        static void Main ()
        {
            Foo foo = JsonConvert.DeserializeObject<Foo>(json, new JsonSerializerSettings {
                Converters = { new BoolConverter() }
            });
            Console.WriteLine(JsonConvert.SerializeObject(foo, Formatting.Indented));
            Console.ReadKey();
        }
    }

    class Foo
    {
        public bool b1, b2, b3;
    }
}

这代码覆盖所有的布尔值的反序列化。如果您需要此只对特定的成员，您需要申请 JsonConverterAttribute 。

This code overrides deserialization of all boolean values. If you need this only for specific members, you need to apply JsonConverterAttribute.

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