QObjectderived

QObject-derived refers to a class that inherits from QObject, the fundamental base class in the Qt framework. In Qt, QObject provides core object-model features that are widely used beyond user interfaces, including a parent-child hierarchy for automatic memory management, an event system, and the signals-and-slots mechanism for inter-object communication. A QObject-derived class can participate in Qt’s meta-object system, enabling runtime type information, dynamic properties, and introspection through the QMetaObject.

To enable signals, slots, and properties, a QObject-derived class must include the Q_OBJECT macro in its declaration. This macro activates the Qt Meta-Object Compiler (moc), which generates additional code necessary for signal-slot connections, property notification, and other meta-object features. Without moc, certain capabilities of QObject-derived classes will not function correctly.

When designing a QObject-derived class, consider ownership and threading. QObject instances can own child objects via the parent parameter; children are automatically deleted when the parent is destroyed. QObject is non-copyable, so objects are managed by pointers. Communication is typically implemented using the connect mechanism, with both old and modern syntaxes available. Properties are declared with Q_PROPERTY and may include READ, WRITE, and NOTIFY attributes for integrated change notification.

QObject-derived classes are common in both GUI and non-GUI Qt code and are often exposed to QML for UI logic. They participate in the event loop and can use timers and event handlers. If a class does not require signals, slots, or runtime meta-information, a plain C++ class may be more appropriate. Qt also offers Q_GADGET for lightweight meta-features without moc requirements.