QJson

http://qjson.sourceforge.net/usage/

Usage

This page provides a quick overview of QJson’s features:

• parsing: from JSON to QVariant.
• serializing: from QVariant to JSON.
• QObject helper: dump and restore QObject’s attributes.

For more details checkout QJson’s documentation.

Parsing: from JSON to QVariant

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

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// 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:

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{ "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:

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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:

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

Serialization: from QVariant to JSON

QVariant objects are converted to a string containing the JSON data.

Let’s declare a QVariant object with some data to convert:

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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;

Now it’s time to create the Serializer:

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QJson::Serializer serializer; bool ok; QByteArray json = serializer.serialize(people, &ok); if (ok) { qDebug() << json; } else { qCritical() << "Something went wrong:" << serializer.errorMessage(); }

The output will be:

1 2	"[ { "Name" : "Bob", "Phonenumber" : 123 }, { "Name" : "Alice", "Phonenumber" : 321 } ]"

It’s possible to tune the indentation level of the resulting string using the Serializer::setIndentMode() method.

QObject helper

QJson provides an helper class for dumping QObject’s attributes to a QVariant and for restoring QObject’s attributes from a QVariantMap.

Let’s define a simple class inhereted from QObject:

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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; };

Dump QObject’s attributes to JSON

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

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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:

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

Restore QObject’s attributes from JSON

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:

1	{ "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:

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Parser parser; QVariant variant = parser.parse(json); Person person; QObjectHelper::qvariant2qobject(variant.toMap(), &person);

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