Qt Igor November 8, 2002 Friday’s HENP Group Meeting

What is Qt? “…multiplatform C++ GUI application framework…” “…Qt is fully object-oriented, easily extensible, and allows true component programming…” Supported platforms MS/Windows (MFC) : from 95 to XP UNIX (X11) : most popular flavors Mac OS X : Embedded : Linux with frame buffer support “…Qt is also the basis of the popular KDE Linux desktop environment…” Qt is a product of Trolltech ( Commercially introduced in early 1996

Versions and availability V2.x :Is free for non-commercial development for all platforms. Licenses: QPL or GPL V3.x : has lots of new stuff compared to v2.x Is free for non-commercial development for UNIX only. Licenses: QPL or GPL. 30 days free evaluation download is available for MS- Windows and Mac OS X. Is available in two editions (see next slide) for commercial software development. Prices vary from $1240 to $4370 per license depending on the total number of clients and the Qt edition. No royalty for resulting applications

Modules and Editions

What makes Qt a “cool” stuff? My personal opinion : It provides “all in one” object oriented framework for the component programming – one of the main practices in the contemporary software development (not in HEP) A collection of services provided through the framework for the applications developers is nearly complete (for majority of desktop applications). It includes famous “triad”: GUI (user interaction) Database (persistency) Networking (distributed programming) QtDesigner Signal-Slot Objects Communication Model

Multi-platform applications development Qt Object Model QtDesigner … Most interesting features

#include int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel hello( " Hello Qt! “, " ", 0 ); app.setMainWidget( &hello ); hello.show(); return app.exec(); }

Qt Object Model Qt is supposed to add an extra flexibility to the plain C++ Object Model with the following extensions : - a mechanism for seamless object communication called signals and slots - queryable and designable object properties - events and event filters - contextual string translation for internationalization - interval driven timers that make it possible to integrate many tasks in an event-driven GUI - hierarchical and queryable object trees that organize object ownership in a natural way - guarded pointers, QGuardedPtr, that are automatically set to 0 when the referenced object is destroyed, unlike normal C++ pointers which become "dangling pointers" when their objects are destroyed

Qt Object Model : 1 The Qt Object Model implementation : - Standard C++ techniques, based on inheritance from QObject base class - Meta Object System provided by Qt's own Meta Object Compiler (“moc”)

Signals and Slots

#include int main( int argc, char **argv ) { QApplication app( argc, argv ); QPushButton quit( “Quit”, 0 ); QObject::connect( &quit, SIGNAL( clicked()), &app, SLOT ( quit())); app.setMainWidget( &quit ); quit.show(); return app.exec(); }

Meta Object System Provides : Signals and Slots mechanism for inter-object communication, runtime type information, and the dynamic property system Is based on : -the QObject class -the Q_OBJECT macro inside the private section of the class declaration - the Meta Object Compiler (moc) to handle C++ extensions

Meta Object System : 1 How it works : A developer writes a file using Qt C++ extension The moc reads a C++ source file. If it finds one or more class declarations that contain the Q_OBJECT macro, it produces another C++ source file which contains the meta object code for the classes that use the Q_OBJECT macro. Among other things, meta object code is required for the signal/slot mechanism, runtime type information and the dynamic property system. The C++ source file generated by the moc must be compiled and linked with the implementation of the class (or it can be #included into the class's source file).

MOC Example class MyClass : public QObject { Q_OBJECT public: MyClass( QObject* parent=0, const char* name=0 ); ~MyClass(); signals: void mySignal(); public slots: void mySlot(); };

MOC Example : 1 class MyClass : public QObject { Q_OBJECT Q_PROPERTY( Priority priority READ priority WRITE setPriority ) Q_ENUMS( Priority ) public:... enum Priority { High, Low, VeryHigh, VeryLow }; void setPriority( Priority ); Priority priority() const; };

QtDesigner Approach

QtDesigner Approach : 1

QtDesigner Approach : 2