使用 json.net 支持 ISupportInitialize

Question

我正在使用 Newtonsoft json.net 序列化程序将我的一些模型序列化为 json。 其中一些是复杂的包含循环引用。由于循环引用不可序列化，因此通过设置ReferenceLoopHandling = ReferenceLoopHandling.Ignore 处理这些引用。 在使用 ISupportInitialize 进行其他序列化后恢复引用。 ISupportInitialize 还用于从数据库初始化重属性（图像）。有些类没有默认 ctor（需要 [NotNull] 参数），我知道我的重属性可能是惰性的，但由于我的 ISupportInitialize 与以前的序列化程序一起工作正常（并且经过测试），我更愿意使用该机制。

我正在尝试让 json.net 序列化程序检测实现 ISupportInitialize 接口的类型并调用适当的接口方法。当实际的序列化/反序列化对象实现接口时，这很简单，但当对象图中的某些属性实现它时，这更难（或者至少对我来说不直观）。我试过写一个自定义转换器，但没有运气。下面是我想要完成的一个简单示例

 public class SupportsInitialize : ISupportInitialize
    {
        public void BeginInit(){throw new NotImplementedException();}

        public void EndInit(){throw new NotImplementedException();}
    }

    [Test]
    public void MakeSerializerCallBeginAndEndInit()
    {
        var supportsInitialize = new ToBeSerialized() {SupportsInitialize = new SupportsInitialize()};
        // before serializing any property implementing ISupportInitialize (ToBeSerialized.SupportsInitialize in this case) its BeginInit should be called
        var json = JsonConvert.SerializeObject(supportsInitialize);
        // after deserializing any property implementing ISupportInitialize its EndInit should be called
        var deserialized = JsonConvert.DeserializeObject<ToBeSerialized>(json); 
    }

    public class ToBeSerialized
    {
        public SupportsInitialize SupportsInitialize { get; set; }
    }

感谢您为我指明正确方向的任何帮助

Answer 1

如果您不想手动将调用BeginInit() 和EndInit() 的[OnDeserializing] and [OnDeserialized] 回调添加到您的每个ISupportInitialize 类型，您可以创建DefaultContractResolver 的自定义子类，它会自动调用适当的方法：

public class ISupportInitializeContractResolver : DefaultContractResolver
{
    // As of 7.0.1, Json.NET suggests using a static instance for "stateless" contract resolvers, for performance reasons.
    // http://www.newtonsoft.com/json/help/html/ContractResolver.htm
    // http://www.newtonsoft.com/json/help/html/M_Newtonsoft_Json_Serialization_DefaultContractResolver__ctor_1.htm
    // "Use the parameterless constructor and cache instances of the contract resolver within your application for optimal performance."
    static ISupportInitializeContractResolver instance;

    // Using a static constructor enables fairly lazy initialization.  http://csharpindepth.com/Articles/General/Singleton.aspx
    static ISupportInitializeContractResolver() { instance = new ISupportInitializeContractResolver(); }

    public static ISupportInitializeContractResolver Instance { get { return instance; } }

    readonly SerializationCallback onDeserializing;
    readonly SerializationCallback onDeserialized;

    protected ISupportInitializeContractResolver()
        : base()
    {
        onDeserializing = (o, context) =>
            {
                var init = o as ISupportInitialize;
                if (init != null)
                    init.BeginInit();
            };
        onDeserialized = (o, context) =>
            {
                var init = o as ISupportInitialize;
                if (init != null)
                    init.EndInit();
            };
    }

    protected override JsonContract CreateContract(Type objectType)
    {
        var contract = base.CreateContract(objectType);
        if (typeof(ISupportInitialize).IsAssignableFrom(objectType))
        {
            contract.OnDeserializingCallbacks.Add(onDeserializing);
            contract.OnDeserializedCallbacks.Add(onDeserialized);
        }
        return contract;
    }
}

然后像这样使用它：

        var settings = new JsonSerializerSettings { ContractResolver = ISupportInitializeContractResolver.Instance };
        var root = JsonConvert.DeserializeObject<ToBeSerialized>(jsonString, settings);

Answer 2

我猜你不需要那个。您可以尝试使用适当的设置进行序列化：

// intended is not needed, but it makes it easier to know whats going on.
var json = JsonConvert.SerializeObject(yourObject, Formatting.Indented, new JsonSerializerSettings
    {
        ReferenceLoopHandling = ReferenceLoopHandling.Serialize,
        PreserveReferencesHandling = PreserveReferencesHandling.Objects
    });

并像往常一样反序列化：

var obj = JsonConvert.DeserializeObject<ToBeSerialized>(json); 

---

要调用您的 Initializ 方法，您可以尝试使用 JSON.NET 的 SerializationCallbacks：

public class ToBeSerialized
{
    // [...]

    // this is probably superflous if the callbacks do what you want, you can move the code there
    public SupportsInitialize SupportsInitialize { get; set; }

    [OnDeserializing]
    internal void OnDeserializingMethod(StreamingContext context)
    {
        this.SupportsInitialize.BeginInit();
    }

    [OnDeserialized]
    internal void OnDeserializedMethod(StreamingContext context)
    {
        this.SupportsInitialize.EndInit();
    }
}