使用 DataContractJsonSerializer，将 JSON 字符串反序列化为具有列表和接口作为属性的 C# 对象

Question

我正在开发一个调用第 3 方 REST 服务的 c#.dotNet 项目。

样本Class结构：

[Serializable]
[DataContract(Name = "MainClass")]
[KnownType(typeof(Class1))]
[KnownType(typeof(Class2))]
public class MainClass : IMainInterface
{

    public MainClass()
    {
        Value2 = new List<IClass2>();
    }

    [DataMember(Name = "class")]
    public IClass1 Value1 { get; set; }

    [DataMember(Name = "classes")]
    public List<IClass2> Value2 { get; set; }

}

[Serializable]
[Export(typeof(IClass1))]
[ExportMetadata("IClass1", "Class1")]
[DataContract(Name = "class1")]
public class Class1 : IClass1
{
    [ImportingConstructor]
    public Class1()
    {

    }

    [DataMember(Name = "prop1")]
    public string Prop1 { get; set; }

    [DataMember(Name = "prop2")]
    public string Prop2 { get; set; }

    [DataMember(Name = "prop3")]
    public string Prop3 { get; set; }

}

[Serializable]
[Export(typeof(IClass2))]
[ExportMetadata("IClass2", "Class2")]
[DataContract]
public class Class2 : IClass2
{
    [ImportingConstructor]
    public Class2()
    { }


    [DataMember(Name = "propA")]
    public string PropA { get; set; }

    [DataMember(Name = "propB")]
    public string PropB { get; set; }

    [DataMember(Name = "propC")]
    public string PropC { get; set; }
}

public interface IMainInterface
{
    IClass1 Value1 { get; set; }

    List<IClass2> Value2 { get; set; }
}

public interface IClass1
{
    string Prop1 { get; set; }

    string Prop2 { get; set; }

    string Prop3 { get; set; }
}

public interface IClass2
{
    string PropA { get; set; }

    string PropB { get; set; }

    string PropC { get; set; }
}

Json_String1：（带有类型提示）

{
"class":
    {"__type":"class1:#WpfApplication1","prop1":"TestVal0","prop2":"TestVal2","prop3":"TestVal3"},
"classes":
    [
        {"__type":"Class2:#WpfApplication1","propA":"A","propB":"B","propC":"C"},
        {"__type":"Class2:#WpfApplication1","propA":"X","propB":"Y","propC":"Z"},
        {"__type":"Class2:#WpfApplication1","propA":"1","propB":"2","propC":"3"}
    ]
}

Json_String2：（无类型提示）

{
"class":
    {"prop1":"TestVal0","prop2":"TestVal2","prop3":"TestVal3"},
"classes":
    [
        {"propA":"A","propB":"B","propC":"C"},
        {"propA":"X","propB":"Y","propC":"Z"},
        {"propA":"1","propB":"2","propC":"3"}
    ]
}

因此，对于给定的 class 结构，如果我使用 DataContractJsonSerializer 生成 json（MainClass 的对象），我将得到 Json_String1 如果我直接反序列化，它工作正常。

而当 GET 获取数据时，响应是 Json_String2（w/o 类型提示）。因此，在反序列化时出现以下错误。

InvalidCastException was unhandled. Unable to cast object of type 'System.Object' to type 'WpfApplication1.IClass2'.

现在，我必须通过添加类型提示手动修改 json（字符串操作），才能成功反序列化它。

问题 1) 如何避免这种 Json 字符串操作反序列化？

问题 2) 如何在没有类型提示的情况下创建 json？

编辑： 1. 新增IMainInterface，由MainClass实现。 2. 点网框架 4

Answer 1

问题是因为您试图反序列化为只有接口的 class。当 JSON 指定 __type 时，它显然有效。但是当它不存在时（就像在您的第二个 JSON 示例中一样），ReadObject 无法自动将接口解析为其实现。

尝试使用 MainClass 中的具体 classes Class1、Class2 而不是它们的接口（IClass1、IClass2）。其余代码可以保持原样。您的两个 Json 示例都可以正常工作。

[Serializable]
[DataContract(Name = "MainClass")]
[KnownType(typeof(Class1))]
[KnownType(typeof(Class2))]
public class MainClass
{

    public MainClass()
    {
        Value2 = new List<Class2>();
    }

    [DataMember(Name = "class")]
    public Class1 Value1 { get; set; }

    [DataMember(Name = "classes")]
    public List<Class2> Value2 { get; set; }

}

Answer 2

由于 none 的 classes 实际上是多态的，因此有几个解决方案可用，它们使用 .Net 内置 class 库：

方案一：JavaScriptSerializer方案

JavaScriptSerializer makes it easy to remap interfaces to classes during deserialization by using a JavaScriptConverter。但是，它不允许重新映射字段和属性名称，因此您的属性名称 必须与 [=49] 中的名称相匹配=] 您希望处理 。以下转换器可以解决问题：

public class InterfaceToClassConverter<TInterface, TClass> : JavaScriptConverter where TClass : class, TInterface
{
    public InterfaceToClassConverter()
    {
        if (typeof(TInterface) == typeof(TClass))
            throw new ArgumentException(string.Format("{0} and {1} must not be the same type", typeof(TInterface).FullName, typeof(TClass).FullName)); // Or else you would get infinite recursion!
        if (!typeof(TInterface).IsInterface)
            throw new ArgumentException(string.Format("{0} must be an interface", typeof(TInterface).FullName));
        if (typeof(TClass).IsInterface)
            throw new ArgumentException(string.Format("{0} must be a class not an interface", typeof(TClass).FullName));
    }

    public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
    {
        if (type == typeof(TInterface))
            return serializer.ConvertToType<TClass>(dictionary);
        return null;
    }

    public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override IEnumerable<Type> SupportedTypes
    {
        get
        {
            // For an interface-valued property such as "IFoo  Foo { getl set; },
            // When serializing, JavaScriptSerializer knows the actual concrete type being serialized -- which is never an interface.
            // When deserializing, JavaScriptSerializer only knows the expected type, which is an interface.  Thus by returning
            // only typeof(TInterface), we ensure this converter will only be called during deserialization, not serialization.
            return new[] { typeof(TInterface) };
        }
    }
}

并像这样使用它：

public interface IMainInterface
{
    IClass1 @class { get; set; } // NOTICE ALL PROPERTIES WERE RENAMED TO MATCH THE JSON NAMES.
    List<IClass2> classes { get; set; }
}

[Serializable]
[DataContract(Name = "MainClass")]
[KnownType(typeof(Class1))]
[KnownType(typeof(Class2))]
public class MainClass : IMainInterface
{
    public MainClass()
    {
        classes = new List<IClass2>();
    }

    [DataMember(Name = "class")]
    public IClass1 @class { get; set; }

    [DataMember(Name = "classes")]
    public List<IClass2> classes { get; set; }
}

[Serializable]
[DataContract(Name = "class1")]
public class Class1 : IClass1
{
    public Class1() {}

    [DataMember(Name = "prop1")]
    public string prop1 { get; set; }

    [DataMember(Name = "prop2")]
    public string prop2 { get; set; }

    [DataMember(Name = "prop3")]
    public string prop3 { get; set; }

}

[Serializable]
[DataContract]
public class Class2 : IClass2
{
    public Class2() { }

    [DataMember(Name = "propA")]
    public string propA { get; set; }

    [DataMember(Name = "propB")]
    public string propB { get; set; }

    [DataMember(Name = "propC")]
    public string propC { get; set; }
}

public interface IClass1
{
    string prop1 { get; set; }
    string prop2 { get; set; }
    string prop3 { get; set; }
}

public interface IClass2
{
    string propA { get; set; }
    string propB { get; set; }
    string propC { get; set; }
}

public static class TestJavaScriptConverter
{
    public static void Test()
    {
        string json = @"
            {
            ""class"":
                {""prop1"":""TestVal0"",""prop2"":""TestVal2"",""prop3"":""TestVal3""},
            ""classes"":
                [
                    {""propA"":""A"",""propB"":""B"",""propC"":""C""},
                    {""propA"":""X"",""propB"":""Y"",""propC"":""Z""},
                    {""propA"":""1"",""propB"":""2"",""propC"":""3""}
                ]
            }";

        var serializer = new JavaScriptSerializer();
        serializer.RegisterConverters(new JavaScriptConverter[] { new InterfaceToClassConverter<IClass1, Class1>(), new InterfaceToClassConverter<IClass2, Class2>() });
        var main1 = serializer.Deserialize<MainClass>(json);
        var json2 = serializer.Serialize(main1);
        Debug.WriteLine(json2);
        var main2 = serializer.Deserialize<MainClass>(json2);

        Debug.Assert(main1.@class.ToStringWithReflection() == main2.@class.ToStringWithReflection()); // No assert
        Debug.Assert(main1.classes.Select(c => c.ToStringWithReflection()).SequenceEqual(main2.classes.Select(c => c.ToStringWithReflection()))); // no assert
    }
}

方案二：DataContractJsonSerializer方案

WCF 及其 DataContractSerializers 仅使用具体类型并且不序列化接口。因此，如果你想使用这些序列化器，你必须在内部使用具体的 classes 并将它们作为接口呈现给外部世界，例如：

public interface IMainInterface
{
    IClass1 Value1 { get; set; }
    IList<IClass2> Value2 { get; set; }
}

[Serializable]
[DataContract(Name = "MainClass")]
public class MainClass : IMainInterface
{
    [DataMember(Name = "class")]
    Class1 RealValue1 { get; set; }

    [DataMember(Name = "classes")]
    private List<Class2> RealList2 { get; set; }

    IList<IClass2> list2Proxy; // can't be readonly because the DataContactJsonSerializer does not call the default constructor.

    private IList<IClass2> List2Proxy
    {
        get
        {
            if (list2Proxy == null)
                Interlocked.CompareExchange(ref list2Proxy, new ConvertingList<Class2, IClass2>(() => this.RealList2, c => c, ToClass), null);
            return list2Proxy;
        }
    }

    Class2 ToClass(IClass2 iClass)
    {
        // REWRITE TO FIT YOUR NEEDS
        return (Class2)iClass;
    }

    Class1 ToClass(IClass1 iClass)
    {
        // REWRITE TO FIT YOUR NEEDS
        return (Class1)iClass;
    }

    public MainClass()
    {
        RealList2 = new List<Class2>();
    }

    [IgnoreDataMember]
    public IClass1 Value1
    {
        get
        {
            return RealValue1;
        }
        set
        {
            RealValue1 = ToClass(value);
        }
    }

    [IgnoreDataMember]
    public IList<IClass2> Value2
    {
        get
        {
            return List2Proxy;
        }
        set
        {
            if (value == null)
            {
                RealList2.Clear();
                return;
            }
            if (List2Proxy == value)
                return;
            RealList2 = value.Select<IClass2, Class2>(ToClass).ToList();
        }
    }
}

public class ConvertingList<TIn, TOut> : IList<TOut>
{
    readonly Func<IList<TIn>> getList;
    readonly Func<TIn, TOut> toOuter;
    readonly Func<TOut, TIn> toInner;

    public ConvertingList(Func<IList<TIn>> getList, Func<TIn, TOut> toOuter, Func<TOut, TIn> toInner)
    {
        if (getList == null || toOuter == null || toInner == null)
            throw new ArgumentNullException();
        this.getList = getList;
        this.toOuter = toOuter;
        this.toInner = toInner;
    }

    IList<TIn> List { get { return getList(); } }

    TIn ToInner(TOut outer) { return toInner(outer); }

    TOut ToOuter(TIn inner) { return toOuter(inner); }

    #region IList<TOut> Members

    public int IndexOf(TOut item)
    {
        return List.IndexOf(toInner(item));
    }

    public void Insert(int index, TOut item)
    {
        List.Insert(index, ToInner(item));
    }

    public void RemoveAt(int index)
    {
        List.RemoveAt(index);
    }

    public TOut this[int index]
    {
        get
        {
            return ToOuter(List[index]);
        }
        set
        {
            List[index] = ToInner(value);
        }
    }

    #endregion

    #region ICollection<TOut> Members

    public void Add(TOut item)
    {
        List.Add(ToInner(item));
    }

    public void Clear()
    {
        List.Clear();
    }

    public bool Contains(TOut item)
    {
        return List.Contains(ToInner(item));
    }

    public void CopyTo(TOut[] array, int arrayIndex)
    {
        foreach (var item in this)
            array[arrayIndex++] = item;
    }

    public int Count
    {
        get { return List.Count; }
    }

    public bool IsReadOnly
    {
        get { return List.IsReadOnly; }
    }

    public bool Remove(TOut item)
    {
        return List.Remove(ToInner(item));
    }

    #endregion

    #region IEnumerable<TOut> Members

    public IEnumerator<TOut> GetEnumerator()
    {
        foreach (var item in List)
            yield return ToOuter(item);
    }

    #endregion

    #region IEnumerable Members

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    #endregion
}

请注意，如果调用者尝试设置 IClass1 或 IClass2 而不是实际的 Class1 或 Class2，则 InvalidCastException 将是抛出。因此，这给出了隐藏接口实现的外观，而没有真正保持实现私有。

使用 DataContractJsonSerializer，将 JSON 字符串反序列化为具有列表和接口作为属性的 C# 对象

Using DataContractJsonSerializer, deserialization of JSON string into C# object which has list & interface as properties

c#

rest

serialization

json

datacontractjsonserializer