QJson

API

The full documentation of QJson can be found here.

Converting JSON to QVariant

Converting JSON's data to QVariant instance is really simple:

          // create a Parser instance
          QJson::Parser parser;

          bool ok;

          // json is a QString containing the data to convert
          QVariant result = parser.parse (json, &ok);
        

Suppose you're going to convert this JSON data:

          {
            "encoding" : "UTF-8",
            "plug-ins" : [
                "python",
                "c++",
                "ruby"
                ],
            "indent" : { "length" : 3, "use_space" : true }
          }
        

The following code would convert the JSON data and parse it:

          QJson::Parser parser;
          bool ok;

          QVariantMap result = parser.parse (json, &ok).toMap();
          if (!ok) {
            qFatal("An error occurred during parsing");
            exit (1);
          }

          qDebug() << "encoding:" << result["encoding"].toString();
          qDebug() << "plugins:";

          foreach (QVariant plugin, result["plug-ins"].toList()) {
            qDebug() << "\t-" << plugin.toString();
          }

          QVariantMap nestedMap = result["indent"].toMap();
          qDebug() << "length:" << nestedMap["length"].toInt();
          qDebug() << "use_space:" << nestedMap["use_space"].toBool();
        

The output would be:

          encoding: "UTF-8"
          plugins:
            - "python"
            - "c++"
            - "ruby"
          length: 3
          use_space: true
        

Converting QVariant to JSON

Converting a QVariant instance into a JSON object is really simple:

          QVariantList people;

          QVariantMap bob;
          bob.insert("Name", "Bob");
          bob.insert("Phonenumber", 123);

          QVariantMap alice;
          alice.insert("Name", "Alice");
          alice.insert("Phonenumber", 321);

          people << bob << alice;

          QJson::Serializer serializer;
          QByteArray json = serializer.serialize(people);

          qDebug() << json;
        

The output will be:

          "[ { "Name" : "Bob", "Phonenumber" : 123 }, { "Name" : "Alice", "Phonenumber" : 321 } ]"
        

QObjct serialization and vice-versa

It's also possible to serialize a QObject instance to JSON. All the class attributes defined as properties will be serialized. Suppose the declaration of Person class looks like this:

          class Person : public QObject
          {
            Q_OBJECT

            Q_PROPERTY(QString name READ name WRITE setName)
            Q_PROPERTY(int phoneNumber READ phoneNumber WRITE setPhoneNumber)
            Q_PROPERTY(Gender gender READ gender WRITE setGender)
            Q_PROPERTY(QDate dob READ dob WRITE setDob)
            Q_ENUMS(Gender)

          public:
              Person(QObject* parent = 0);
              ~Person();

              QString name() const;
              void setName(const QString& name);

              int phoneNumber() const;
              void setPhoneNumber(const int  phoneNumber);

              enum Gender {Male, Female};
              void setGender(Gender gender);
              Gender gender() const;

              QDate dob() const;
              void setDob(const QDate& dob);

            private:
              QString m_name;
              int m_phoneNumber;
              Gender m_gender;
              QDate m_dob;
          };
        

The following code will serialize an instance of Person to JSON:

          Person person;
          person.setName("Flavio");
          person.setPhoneNumber(123456);
          person.setGender(Person::Male);
          person.setDob(QDate(1982, 7, 12));

          QVariantMap variant = QObjectHelper::qobject2qvariant(&person);
          Serializer serializer;
          qDebug() << serializer.serialize( variant);
        

The generated output will be:

          { "dob" : "1982-07-12", "gender" : 0, "name" : "Flavio", "phoneNumber" : 123456 }
        

It's also possible to initialize a QObject using the values stored inside of a QVariantMap. Suppose you have the following JSON data stored into a QString:

          { "dob" : "1982-07-12", "gender" : 0, "name" : "Flavio", "phoneNumber" : 123456 }
        

The following code will initialize an already allocated instance of Person using the JSON values:

          Parser parser;
          QVariant variant = parser.parse(json);

          Person person;
          QObjectHelper::qvariant2qobject(variant.toMap(), &person);