Introduction to QtBuild Great Apps Using Qt

Jeff Alstadt

My name is Jeff Alstadt I

work as a Senior Developer at Litholink, a LabCorp company

am a passionate C/C++ and .NET developer worked with Qt in 2011 while at Centare love open source and believe it is the right way

to do software development am an avid technical speaker and blogger

Introduction

Today we are talking about

This Is Qt 5

Qt is an open source cross platform UI toolkit for the C++ platform

Qt is used by over 500,000 developers Although digia has taken over support the Qt

project, Qt is still a strong contender for embedded Linux (RTOS), desktop UI development (Windows, Mac and Linux), and mobile devices (tablet, phone)

What is Qt?

Qt was founded in 1991 in Oslo, Norway by Erik Chambe-Eng and Haavard Nord

Both Erik and Haavard had founded Trolltech on 4 March 1994.

Trolltech‘s IPO came on the Oslo Stock Exchange in July 2006

In 2001 Qt introduced Qtopia which was an application platform for embedded Linux-based devices such as mobile phones, home media and etc.

Qt Founders

Qt Founders

The toolkit was called Qt becuase the letter Q looked appealing in Haavard‘s Emacs font and “t“ was inspired by Xt, the X toolkit

So what does the Qt ecosystem look like

Actually not, over 500,000 developers have applications built on Qt technology

Even though Nokia sold Qt to Digia, Digia has promised 15 M Euro investment in Qt research and development and ecosystem activities

Commercial licensing ensures future funding of Qt development

The next Blackberry will be using Qt as its UI framework

Qt mobile apps have been successfully ported to iOS and Android

But isn’t Qt dead?

#1 in multi-platform support #1 in developer experience #1 in creating great user experiences Belief in dual licensing model Strong value generating ecosystem Open business architecture

Digia’s Goals for Qt

Actually Qt is enabled for the web. Using Qt WebKit Qt developers can develop apps using C++, QML and HTML5/JavaScript.

Qt WebKit provides facilities for rendering of HTML, XHTML, SVG, CSS and JavaScript

QtWebKit Bridge provides a bridge between the JavaScript execution environment and the Qt object model.

Qt Webkit is based on the Open Source WebKit Engine

But Qt can’t handle web…

The Tulip Container Classes The Arthur Paint System The Interview Framework The Scribe Classes Qt Main Window Classes Graphics View Qt Network Module Resource System Unit Testing Framework

Fundamental Technologies of Qt

Qt Creator – cross platform C++ debugger and developer designed specifically for Qt

Qt Visual Studio add-in – provides Qt integration with Visual Studio 2008, 2010 and 2012

Qt Simulator - A fast and lightweight simulator for Qt applications running on Nokia devices.

Eclipse Integration Plugin Qt Teambuilder – distributed C/C++compilation Qt Mobility – mobile API Qt SDK Qt Quick Qt Webkit

Qt Development Tools

The Qt Lighthouse project was a project started to gain advancement in providing Qt ports to iOS and Android

The Lighthouse project is the project that will allow Qt to be deployed on mobile devices

Qt Lighthouse

The Necessitas project is a community driven Lighthouse based port of Qt to Android

It has a plugin for Qt Creator to do Android development

An installer application for Android called Ministro exists Ministro is responsible for downloading the Qt

libraries specific to that Android device

Qt Meets Android

The Qt Lighthouse project was an initiative to get Qt running on the iOS platforms.

Qt Meets iOS

Qt Overall Architecture

Here we will get into Qt concepts QObject Meta Object Compiler (MOC) Qt Container Classes Signal Slot System Qt Property System Qt Event System Qt Model View Concept Qt Widgets (QWidget) Qt Graphic View (QGraphicView)

Let’s get technical with Qt

Most objects in Qt inherit from QObject This provides your custom Qobject classes to

have Signals and slots support Property Support Memory Management Support Introspection

QObject

A program that handles Qt’s C++ Extensions How it works:

Moc looks for the Q_OBJECT macro Once found moc will produce a C++ source file containing

the meta-object code that is required for Signals and slot mechanism Run-time type information Dynamic Property System

Moc produces another header and source file with the moc_mycppfile.cpp These need to be included in the make file so that the code

can be compiled and linked.

Meta Object Compiler

Qt utilizes many of the STL collection classes and introduces some of its own

These include QList QMap QStack QQueue QSet QHashMap QVector

Qt Container Classes

Specific concept in Qt every Qt developer needs to know

Implements simple Observer Pattern

Type safe Decoupled Objects inherited from

QObject will only receive the signal notifcations

connect connects the object signal to the respective slot

Signals and Slots

Signal Slot Code Example

The Qt system provides a means to set any property in the Qt Meta-Object System

The Qt solution works with any standard C++ compiler Qt supports

Q_PROPERTY is a macro that is used to declare property

This declaration must be done inside a QObject

Qt Property System

An event is an object or a set of objects derived from the abstract class QEvent

Events represent things that have happened either within an application or as a result of outside activity that the application needs to know about

Events are recieved and handled by instance of a derived QObject class

Qt Event System

QResizeEvent (Window Resizing) QPaintEvent (Window Repainting) QMouseEvent (Mouse Input) QKeyEvent (Keyboard Input) QCloseEvent (Window close)

Common Qt Events

In Qt, we can utilize the QCoreApplication to create and send our own custom events.

To do this, we utilize sendEvent() and postEvent(). sendEvent() processes the event immediatly. postEvent() posts the event on queue for later dispatch

When Qt‘s main event loop runs, it will then dispatch all posted events.

To create a custom Qt Event type, simpily subclass your event from QEvent and ensure it has an event number that is greater than QEvent::User (1000 presently in 4.8)

For all events, check here

Sending Events

Qt has an advanced Model View archictecture concept that was inspired from the MVC approach

Instead Qt utilizes a delegate instead of a controller

The delegate is used to provide a fine control over how items are rendered and edited

For Qt specific views, Qt provides the appropriate delegate for that view

Model View

QStringListModel QStandardItemModel QDirModel QSqlQueryModel QSqlTableModel QSqlRelationalTableModel QSortFilterProxyModel

Commonly Used Qt Model Classes

QGraphicsView – a view for fast structured 2D graphics Graphics items known as QGraphicItems are placed in

a scene known as QGrahpicsScene A scene is then displayed in one or more views

(QGraphicViews) Graphic items can be

lines, rectangesl polygons, pixmaps, ellipses, text, SVG drawings, widgets or any customizable item you can think of

moved, scaled, rotated

Graphics View

QGraphicsItems are lightweight compared to QWidget This allows for thousands of these guys to exist while not

taking a hit on performance or memory QGraphItems can be arbitrarily transformed

(QTransform) Support for high quality zooming for example

Graphics Items have there own internal event system that is slightly different than the regular QEvent system

Widgets can be embedded into a graphics scene by using the QGraphicsProxyWidget

Graphics Items

#include <QtGui>

int main(int argc, char **argv) {QApplication app(argc, argv);QGraphicsScene scn;

QGraphicsEllipseItem ellipse(-10, -10, 120, 50);scn.addItem(&ellipse);

QGraphicsTextItem text(“Hello World”);scn.addItem(&text);

QGraphicsView view(&scn);view.show();return app.exec():

}

Hello World Graphics View Example

http://qt-project.org/videos/watch/programming_with_qt_qgraphicsview_by_kdab

http://qt-project.org/videos/watch/programming_with_qt_qgraphicsview_by_ics

For More About QGraphicViewCheck these Videos:

Qt supports Unicode via QString Support for Right-to-Left (Chinese) Read/Write files in different codecs Layout system can be internationalized Qt Linguist applications allows apps to be

translated easily

Internationalization

“Translating Qt Applications” – Benjamin Poulainhttp://qt-project.org/videos/watch/translating_qt_applications

To learn more on Internationalization see

Shared memory TCP/UDP Sockets (QSocket) HTTP/FTP protocol support D-Bus

Interprocess Communication (IPC)

Introduced in Qt 4.6 and part of QtCore module Originated from Qt-SCXML research project SMF provides the means to create heirarchical

finite state machines (HFSMs) SMF also provides an “interpreter” for executing

HFSMs Helps to reduce spaghetti code by

By making if statements implicit since state is implicit Producing clear control flow

Qt State Machine Framework (SMF)

State Machine Framework http://

www.slideshare.net/qtbynokia/qt-state-machine-framework -Slides

http://qt-project.org/videos/watch/state_machine_framework - Video

For more learning on Qt State Machines

Qt supports test driven development (TDD) Using QTestLib, Qt developers can do unit tests Qt supports

Basic Unit Testing Data Driven Testing Cross-Platform and Cross-Compiler Unit Tests Stand alone unit tests Memory Debugging Integrations

Unit Testing

QVERIFY Evaluates complex expressions

QCOMPARE Compares two values using the respective

object comparison operator

Qt Unit Test Macros

class QStringTest : public QObject {Q_OBJECT

private slots:void toUpper(){

QString str(“hello world”);QCOMPARE(str.toUpper(),

Qstring(“HELLO WORLD”));}

};

Hello World Unit Test Example

Allows for separation of logic and data Improved readability Easily extendable Reduction of copy and pasting of code in test

code Ease in testing the border cases of the

application

Benefits of Data Driven Tests

QtTestLib offers non-native mouse and keyboard simulation support for QWidgets

Very basic support for replay eventa 3rd party tools such as Squish and KD

Executer

Coded UI Test Support

Squish - http://qt-project.org/wiki/Category:Tools::Squish

Unit Testing in Qt Applications by Harald Fernengel http://qt-project.org/videos/watch/unit_testing_in_qt_applications

Learn more about Qt Unit Testing

Qt provides QBENCHMARK to measure code QBENCHMARK measures code based on

Walltime (default) CPU Tick Count (-tickcounter) Valgrind/Callgrind (-callgrind) Event counter (-eventcounter)

Performance

TOC was developed by Eliyahu M. Goldratt Basically TOC is a theory which says that given

a complex system, there is usually one aspect of that system that will limits it ability to achieve its goal or optimal functioning. Before an achievement of any significant improvement of the system can be achieved, the constraint or bottleneck must be first identified and resolved Reduce Bottlenecks improve Performance

Theory of Constraints

Choose the right container Utilize implicit data sharing efficiently

ExampleObject obj0;Object obj1, obj2, obj3 = obj0 Here data is only copied if some other guy modifies it since

Object 1 will have deep copy of object ObjectData and Object 2 and Object 3 will only have shallow copies

Avoid deep-copy, its expensive Pass objects around as const references Only use const operators and functions if possible

Avoid bottlenecks

Qt Optimization Techniques

Optimizing Performance in Qt Based Applications - Bjørn Erik Nilsen http://www.slideshare.net/qtbynokia/optimizing-performance-in-qtbased-applications

To learn more about Optimizing your Qt Apps check

Thanks