Newtonsoft.json processing of deserialization of polymorphic types

The serialization and deserialization of Newtonsoft.json is very mature and useful, and recently encountered a problem in the deserialization of a polymorphic type, which can only be converted to a base class after deserialization, but not to a subclass. After a query from the Internet, you need to write a type of converter, below we step by step:

1. First describe the definition of the type, in order to do this experiment, I define a base class and two subclasses, and then I want to serialize the object containing the collection of this base class.

namespacelexsry{usingNewtonsoft.json; usingSystem.Collections.Generic; classDemodata {[Jsonproperty ("demoid")]         Public intdemoid {Get;Set; } [Jsonproperty ("Demos")]         PublicList<demobase> Demos {Get;Set; } }     Public classdemobase {[Jsonproperty ("ID")]         Public intId {Get;Set; } [Jsonproperty ("name")]         Public stringName {Get;Set; } [Jsonproperty ("type")]         Public stringType {Get;Set; } }     Public classdemoa:demobase {[Jsonproperty ("Color")]         Public stringColor {Get;Set; } }     Public classdemob:demobase {[Jsonproperty ("size")]         Public Double[] Size {Get;Set; } }}

2. Serialization, deserialization method. Use JsonConvert when deserializing. deserializeobject<T> (string value, param jsonconverter[] converter). Create the appropriate subclass by defining jsonconverter yourself.

in this demo, I first created an abstract classJsoncreationconverter<T:Jsonconverter,

second, for the Demobase, I created aJsondemoconverter:Jsoncreationconverter<Demobase>

    classJsonParser3 { Public Static voidWritejson (ObjectTstringfile) {Jsonserializer Serializer=NewJsonserializer (); using(StreamWriter SW =NewStreamWriter (file)) {                using(Jsonwriter writer =NewJsonTextWriter (SW)) {Serializer.                Serialize (writer, t); }            }        }         Public Static voidReadjson<t> (stringFile outT obj) {Jsonserializer Serializer=NewJsonserializer (); using(StreamReader sr =NewStreamReader (file)) {obj= Jsonconvert.deserializeobject<t> (sr.) ReadToEnd (),NewJsondemoconverter ()); }        }    }     Public Abstract classJsoncreationconverter<t>: jsonconverter {protected AbstractT Create (Type objectType, Jobject jsonobject);  Public Override BOOLCanconvert (Type objectType) {return typeof(T).        IsAssignableFrom (ObjectType); }         Public Override ObjectReadjson (Jsonreader Reader, Type ObjectType,ObjectExistingvalue, Jsonserializer Serializer) {            varJsonobject =jobject.load (reader); vartarget =Create (ObjectType, jsonobject); Serializer.            Populate (Jsonobject.createreader (), target); returnTarget; }         Public Override voidWritejson (Jsonwriter writer,Objectvalue, Jsonserializer serializer) {            Throw Newnotimplementedexception (); }    }     Public classJsondemoconverter:jsoncreationconverter<demobase>    {        protected Overridedemobase Create (Type objectType, Jobject jsonobject) {varTypeName = jsonobject["type"].            ToString (); Switch(typeName) { Case "A":                    return NewDemoa ();  Case "B":                    return Newdemob (); default:return NULL; }        }    }}

3. Implement the serialization of in-memory objects into Test.json in code, and then deserialize the data from Test.json to the memory object ndata:

Demodata data =NewDemodata () {demoid=1, Demos=NewList<demobase>()                {                    NewDemoa () {id=1, name="Demoa", type="A", color="Red" },                    NewDemob () {id=2, name="", type="B", size=New Double[]{Ten,Ten} }                }            }; Jsonparser3.writejson (data,"Test.json"); Demodata Ndata=NewDemodata (); Jsonparser3.readjson<DemoData> ("Test.json", outNdata);

4. Data in Test.json:

{  "demoid": 1,  "demos": [    {      "color": "Red",      "id": 1,       "name": "Demoa",      "type": "A"    },    {      "size": [10.0, 10.0 ],       "id": 2,      "name": "",      "type": "B"    }  ]}

5. After deserialization, the object obtained in memory Ndata

Newtonsoft.json processing of deserialization of polymorphic types