What does qt mean

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Published Date:28-07-2017
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Introduction to GUI development using Qt Paolo Quadrani – p.quadranicineca.it Andrea Negri – a.negricineca.it SuperComputing Applications and Innovation DepartmentWhat is Qt ● Qt is a cross-platform development framework written in C++ ● Can be used in several programming languages through bindings ● Ruby ● Java ● Perl ● Python → PyQt ● The Qt Toolkit is a collection of classes for various purposes ● Database management ● XML ● WebKit ● Multimedia ● Networking ● ... ● For desktop, mobile and embedded development ● Used by more than 350,000 commercial and open source developers ● Backed by Qt consulting, support and training ● Trusted by over 6,500 companies worldwideQt modulesQt brief timeline ● Qt Development Frameworks founded in 1994 ● Trolltech acquired by Nokia in 2008 ● Qt Commercial business acquired by Digia in 2011 ● Qt business acquired by Digia from Nokia in 2012Why Qt • Write code once to target multiple platforms • Produce compact, high-performance applications • Focus on innovation, not infrastructure coding • Choose the license that fits you • Commercial, LGPL or GPL • Count on professional services, support and trainingPyQt ● PyQt is a set of Python bindings for Qt framework ● Bindings implemented as Python modules (620+ classes) ● Almost the entire Qt library is available ● Take advantage of both languages key strength ● Python: easy to learn, lot of extensions, no compilation required ● Qt: abstraction of platform-specific details, GUI designer“Hello world” in PyQt 1/2 from PyQt4.QtCore import from PyQt4.QtGui import import sys app = QApplication(sys.argv) PushButton = QPushButton("Hello World") PushButton.show() sys.exit(app.exec_())“Hello world” in PyQt 2/2 sys module needed to access command-line arguments QtCore and QtGui (from PyQt4 library) contains GUI widgets Every PyQt application must have a QApplication object Create a new instance of a QPushButton Call show() to schedule a “paint event” The call to app.exec_() starts the event loopCore typesQObject QObject is the heart of Qt's object model Include these features: ● Memory management ● Object properties ● Introspection ● Signals and slots ● Event handling QObject has no visual representationObject tree ● QObjects organize themselves in object trees ● Based on parent-child relationship ● QObject (QObject parent = 0) ● Parent adds object to list of children ● Parent owns children ● Used intensively with QWidget Parent-child relationship IS NOT inheritanceQt's Widget Model - QWidget ● Derived from QObject ● Adds visual representation ● Receives events ● e.g. mouse, keyboard events ● Paints itself on screen ● Using stylesObject Tree and QWidget ● new QWidget(0) ● Widget with no parent = "window" ● QWidget children ● Positioned in parent's coordinate system ● Clipped by parent's boundaries ● QWidget parent ● Propagates state changes ● hides/shows children when it is hidden/shown itself ● enables/disables children when it is enabled/disabled itselfWidgets containing other widgets ● Container Widget ● Aggregates other child-widgets ● Use layouts for aggregation ● QHBoxLayout, QVBoxLayout, QGridLayout ● Note: Layouts are not widgets ● Layout Process ● Add widgets to layout ● Layouts may be nested ● Set layout on container widget ● Hint: use QtDesigner to apply layoutsLayout: examples QGridLayoutObject communication ● Between objects ● Signals & Slots ● Between Qt and the application ● Events ● Between Objects on threads ● Signal & Slots + EventsCallbacks General Problem How do you get from "the user clicks a button" to your business logic? Possible solutions: ● Callbacks • Based on function pointers • Not type-safe • Observer Pattern (Listener) • Based on interface classes • Needs listener registration • Many interface classes • Qt uses • Signals and slots for high-level (semantic) callbacks • Virtual methods for low-level (syntactic) events.Signals and slots ● Every PyQt object deriving from QObject supports S&S mechanism ● Widgets emit signals ● A signal announce state changes: ● a button was clicked ● a checkbox is checked/unchecked ● editing in a text field finished ● Widgets react to a signal through slots ● Connections are used to link signals and slots Signals & Slots 1/8Signals & Slots 2/8

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