Flavio Castelli

Some days ago I introduced the possibility to serialize a QObject instance to JSON. Today I’m going to show you the opposite operation: initializing a QObject using a JSON object.

I refactored a bit my latest changes: I created a new class called QObjectHelper that provides the methods required to convert a QObject instance to a QVariantMap and vice-versa.

This class can be used in conjunction with the Serializer and Parser classes to serialize and deserialize QObject instances to and from JSON.

Let me show a quick example, 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;
};

From QObject to JSON

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 }

From JSON to QObject

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);

A new release

These changes have been included inside the new release of QJson: 0.7.0.

Packages for openSUSE are building right now.

Bookmark It

Hide Sites

This entry was posted on Friday, December 4th, 2009 at 1:07 am and is filed under C++, KDE, Qt. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.