Question

使用自定义JsonConverter转换我的JSON对象。这是通过JsonConverter属性到

下面的IQuery对象实现的

[JsonConverter(typeof(CustomConverter<IQuery>))]
public interface IQuery
{
}

下面是自定义泛型类（为简洁起见，删除了一些位）

public class CustomConverter<T> : JsonConverter
{
    // This should be created via AutoFac
    public ICustomObjectCreator<T> ObjectCreator { get; set; }

    // This default constructr always gets called
    public CustomConverter() {}

    // I want to call this constructor
    [JsonConstructor]
    public CustomConverter(ICustomObjectCreator<T> objectCreator)
    {
        Context = context;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;

        // Load JObject from stream 
        var jObject = JObject.Load(reader);

        // Create target object based on JObject 
        var target = Create(objectType, jObject);

        // Populate the object properties 
        serializer.Populate(jObject.CreateReader(), target);

        return target;
    }

    protected T Create(Type objectType, JObject jObject)
    {
        var type = jObject.GetValue("type", StringComparison.OrdinalIgnoreCase)?.Value<string>();
        return ObjectCreator.Create(type);
    }
}

ICustomObjectConverter接口很简单

public interface ICustomObjectCreator<out T>
{
    T Create(string type);
}

及其实施之一

public class QueryObjectCreator : ICustomObjectCreator<IQuery>
{
    public IQuery Create(string type)
    {
        // ... some logic to create a concrete object
        return (IQuery)concreteObject;
    }
}

最后，Autofac有权遵守上述

builder.RegisterType<QueryObjectCreator>()
       .As<ICustomObjectCreator<IQuery>>()
       .InstancePerLifetimeScope();

问题：

调用CustomJsonConverter时，仅调用其默认构造函数。永远不会调用JsonConstructor。
如果删除默认构造函数，则永远不会调用整个JsonConverter！

我有一个inklinkg，在调用JsonConverter时从不调用AutoFac。我甚至尝试了属性注入来显式构造QueryObjectConstruct，但即使是从未调用过。如何让它工作，以便我的QueryObjectCretor通过DI注入？

我找到了关于依赖注入和JSON.net反序列化的this文章。但是，这是使用DeserializeObject＆lt;＆gt;（）调用进行手动解析，如果它可以工作，我怎么能使它与JsonConverter属性一起使用？

由于

Answer 1

您可以执行以下步骤来实现目标：

为ICustomObjectCreator界面创建非通用界面，以便更方便地创建对象。
介绍一个通用ObjectCreatorBase<T>基类，它调用您的通用Create方法。
创建并设置JsonConvert使用的默认设置。
将AutofacContractResolver设为ContractResolver。

请参阅以下示例以帮助您入门：

void Main()
{
    var builder = new ContainerBuilder();

    builder.RegisterType<QueryObjectCreator>()
        .As<ICustomObjectCreator<IQuery>>()
        .InstancePerLifetimeScope();

    var container = builder.Build();

    Func<JsonSerializerSettings> settingsFactory = () =>
    {
        var settings = new JsonSerializerSettings();
        settings.ContractResolver = new AutofacContractResolver(container);

        return settings;
    };

    JsonConvert.DefaultSettings = settingsFactory;

    var myObject = new MyObject { Query = new Query(42) };

    var json = JsonConvert.SerializeObject(myObject);

    myObject = JsonConvert.DeserializeObject<MyObject>(json);
    Console.WriteLine(myObject.Query.MyProperty);
}

// Define other methods and classes here
public class AutofacContractResolver : DefaultContractResolver
{
    private readonly IContainer _container;

    public AutofacContractResolver(IContainer container)
    {
        _container = container;
    }

    protected override JsonObjectContract CreateObjectContract(Type objectType)
    {
        JsonObjectContract contract = base.CreateObjectContract(objectType);

        var customObjectCreatorType = typeof(ICustomObjectCreator<>).MakeGenericType(objectType);

        if (!_container.IsRegistered(customObjectCreatorType))
            return contract;

        var customObjectCreator = (ICustomObjectCreator) _container.Resolve(customObjectCreatorType);

        // I don't know how you want to obtain the string which shall be passed to CreateObject
        contract.DefaultCreator = () => customObjectCreator.CreateObject("XYZ");
        return contract;
    }
}

public interface ICustomObjectCreator
{
    object CreateObject(string type);
}

public interface ICustomObjectCreator<out T> : ICustomObjectCreator
{
    T Create(string type);
}

public abstract class ObjectCreatorBase<T> : ICustomObjectCreator<T>
{
    public object CreateObject(string type)
    {
        return Create(type);
    }

    public abstract T Create(string type);
}

public class QueryObjectCreator : ObjectCreatorBase<IQuery>
{
    public override IQuery Create(string type)
    {
        Console.WriteLine("Create called");

        // ... some logic to create a concrete object
        var concreteObject = new Query();
        return (IQuery)concreteObject;
    }
}

public interface IQuery
{
    int MyProperty { get; set; }
}

public class Query : IQuery
{
    public int MyProperty { get; set; }

    public Query()
    {
    }

    public Query(int myProperty)
    {
        MyProperty = myProperty;
    }
}

public class MyObject
{
    public IQuery Query { get; set; }
}

输出应为

Create called
42

也许您可以通过简单地使用Autofac直接创建对象来删除所有ICustomObjectCreator个实例来简化代码。

更新

第一种方法有效，但它没有考虑到你需要一个字符串来决定你正在创建哪种对象（type）。

要实现这一点，您可以执行以下操作：

将CustomConverter注册为通用。
如果已为该类型注册任何ResolveContractConverter，则覆盖ICustomObjectCreator方法以返回转换器的实例。
更改DefaultSettings，以便AutofacContractResolver将被使用。

请参阅以下示例：

void Main()
{
    var builder = new ContainerBuilder();

    builder.RegisterType<QueryObjectCreator>()
        .As<ICustomObjectCreator<IQuery>>()
        .InstancePerLifetimeScope();

    builder.RegisterGeneric(typeof(CustomConverter<>)).AsSelf().InstancePerLifetimeScope();

    var container = builder.Build();

    Func<JsonSerializerSettings> settingsFactory = () =>
    {
        var settings = new JsonSerializerSettings();
        settings.ContractResolver = new AutofacContractResolver(container);

        return settings;
    };

    JsonConvert.DefaultSettings = settingsFactory;

    var myObject = new MyObject { Query = new Query(42) };

    var json = JsonConvert.SerializeObject(myObject);

    myObject = JsonConvert.DeserializeObject<MyObject>(json);
    Console.WriteLine(myObject.Query.MyProperty);
}

// Define other methods and classes here
public class AutofacContractResolver : DefaultContractResolver
{
    private readonly IContainer _container;

    public AutofacContractResolver(IContainer container)
    {
        _container = container;
    }

    protected override JsonConverter ResolveContractConverter(Type objectType)
    {
        var customObjectCreatorType = typeof(ICustomObjectCreator<>).MakeGenericType(objectType);
        if (!_container.IsRegistered(customObjectCreatorType))
            return base.ResolveContractConverter(objectType);

        var customConverterType = typeof(CustomConverter<>).MakeGenericType(objectType);
        return (JsonConverter) _container.Resolve(customConverterType);
    }
}

public class CustomConverter<T> : JsonConverter
{
    // This should be created via AutoFac
    public ICustomObjectCreator<T> ObjectCreator { get; }

    // This default constructr always gets called
    public CustomConverter() { }

    // I want to call this constructor
    public CustomConverter(ICustomObjectCreator<T> objectCreator)
    {
        Console.WriteLine("Constructor called");
        ObjectCreator = objectCreator;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;

        // Load JObject from stream 
        var jObject = JObject.Load(reader);

        // Create target object based on JObject 
        var target = Create(objectType, jObject);

        // Populate the object properties 
        serializer.Populate(jObject.CreateReader(), target);

        return target;
    }

    protected T Create(Type objectType, JObject jObject)
    {
        var type = jObject.GetValue("type", StringComparison.OrdinalIgnoreCase)?.Value<string>();
        return ObjectCreator.Create(type);
    }
}

public interface ICustomObjectCreator<out T> 
{
    T Create(string type);
}

public class QueryObjectCreator : ICustomObjectCreator<IQuery>
{
    public IQuery Create(string type)
    {
        Console.WriteLine("Create called");

        // ... some logic to create a concrete object
        var concreteObject = new Query();
        return (IQuery)concreteObject;
    }
}

public interface IQuery
{
    int MyProperty { get; set; }
}

public class Query : IQuery
{
    public int MyProperty { get; set; }

    public Query()
    {
    }

    public Query(int myProperty)
    {
        MyProperty = myProperty;
    }
}

public class MyObject
{
    public IQuery Query { get; set; }
}

输出应为

Constructor called
Create called
42

以下是样本的.NET Fiddle link。

JsonConverter属性：使用自定义构造函数和Autofac反序列化

1 个答案:

更新