c# - DataContract 序列化异常(数据契约名称不是预期的)

Question

我有以下代码:

[DataContract]
class TestContract {
    private String _Name;
    private Int32 _Age;

    [DataMember( Name = "Name" )]
    public String Name {
        get { return _Name; }
        set { _Name = value; }
    }

    [DataMember( Name = "Age" )]
    public Int32 Age {
        get { return _Age; }
        set { _Age = value; }
    }
}

[Serializable]
public class DNCJsonDictionary<K, V> : ISerializable {
    Dictionary<K, V> dict = new Dictionary<K, V>();

    public DNCJsonDictionary() { }

    protected DNCJsonDictionary( SerializationInfo info, StreamingContext context ) {
    }

    public void GetObjectData( SerializationInfo info, StreamingContext context ) {
        foreach( K key in dict.Keys ) {
            info.AddValue( key.ToString(), dict[ key ] );
        }
    }

    public void Add( K key, V value ) {
        dict.Add( key, value );
    }

    public V this[ K index ] {
        set { dict[ index ] = value; }
        get { return dict[ index ]; }
    }
}

public class MainClass {
    public static String Serialize( Object data ) {
        var serializer = new DataContractJsonSerializer( data.GetType() );
        var ms = new MemoryStream();
        serializer.WriteObject( ms, data );

        return Encoding.UTF8.GetString( ms.ToArray() );
    }

    public static void Main() {
        DNCJsonDictionary<String, Object> address = new DNCJsonDictionary<String, Object>();
        address[ "Street" ] = "30 Rockefeller Plaza";
        address[ "City" ] = "New York City";
        address[ "State" ] = "NY";

        TestContract test = new TestContract();
        test.Name = "CsDJ";
        test.Age = 28;

        DNCJsonDictionary<String, Object> result = new DNCJsonDictionary<String, Object>();
        result[ "foo" ] = "bar";
        result[ "Name" ] = "John Doe";
        result[ "Age" ] = 32;

        result[ "Address" ] = address;

            // ** --- THIS THROWS AN EXCEPTION!!! --- **            
        result[ "test" ] = test;

        Console.WriteLine( Serialize( result ) );

        Console.ReadLine();
    }
}

当我运行时，我得到这个异常:

Type 'Json_Dictionary_Test.TestContract' with data contract name 'TestContract:http://schemas.datacontract.org/2004/07/Json_Dictionary_Test' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

但是我不明白!据我所知，KnownTypeAttribute只是在反序列化中使用，如果有继承，不是吗？但这里只是连载。没有数据契约(Contract)成员也能正常工作。

有什么想法吗？

---

我发现了一些有用的东西!有一个带有 KnownTypes 列表的父类，我用所有子类填充它，并将用于序列化:

[DataContract]
[KnownType( "GetKnownTypes" )]  // for serialization
class ResultContract {
    private static List<Type> KnownTypes { get; set; }

    public static List<Type> GetKnownTypes() {
        return KnownTypes;
    }

    static ResultContract() {
        KnownTypes = new List<Type>();
        try {
            foreach( Type type in Assembly.GetExecutingAssembly().GetTypes() ) {
                if( !type.IsAbstract && type.IsSubclassOf( typeof( ResultContract ) ) ) {
                    KnownTypes.Add( type );
                }
            }
        } catch( Exception ex ) {
            Console.WriteLine( "Fatal error!" );
        }
    }
}

[DataContract]
class TestContract : *ResultContract* {
    ...
}
...

Answer 1

添加这一行:

 [KnownType(typeof(TestContract))]

这样

[Serializable]
[KnownType(typeof(TestContract))]
public class DNCJsonDictionary<K, V> : ...

这是一个已知问题。这就是泛型不适用于 WCF 的原因。

但原因很简单，WCF 应该创建 WSDL 并能够发布您的契约(Contract)。使用泛型来定义您的契约(Contract)很好，但 WSDL 需要指向某个具体类，因此您需要 KnownType。