The slides from a Qt workshop held on a FSCONS Hacknight. Video of the first half is available from here: http://vimeo.com/22332184

1. . An Introduction to Qt and Workshop Qt in Education

2. http://www.pelagicore.com/documents/2011-Apr-QtWorkshop.odp © 2011 Nokia Corporation and its Subsidiary(-ies). The enclosed Qt Materials are provided under the Creative Commons Attribution-Share Alike 2.5 License Agreement. The full license text is available here: http://creativecommons.org/licenses/by-sa/2.5/legalcode . Nokia, Qt and the Nokia and Qt logos are the registered trademarks of Nokia Corporation in Finland and other countries worldwide.

4. Thesis work within embedded Linux, open source and design

8. All code is still plain C++ foreach (int value, intList) { … } QObject *o = new QPushButton; o->metaObject()->className(); // returns ”QPushButton” connect(button, SIGNAL(clicked()), window, SLOT(close()));

10. Mac OS X

11. Linux/Unix X11

13. Symbian

14. Maemo

17. Hello World

18. Hello World #include <QApplication> #include <QLabel> int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel l( &quot;Hello World!&quot; ); l.show(); return app.exec(); }

19. Hello World #include <QApplication> #include <QLabel> int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel l( &quot;Hello World!&quot; ); l.show(); return app.exec(); }

20. Hello World #include <QApplication> #include <QLabel> int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel l( &quot;Hello World!&quot; ); l.show(); return app.exec(); }

21. Hello World #include <QApplication> #include <QLabel> int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel l( &quot;Hello World!&quot; ); l.show(); return app.exec(); }

22. Hello World #include <QApplication> #include <QLabel> int main( int argc, char **argv ) { QApplication app( argc, argv ); QLabel l( &quot;Hello World!&quot; ); l.show(); return app.exec(); }

24. They are placed in a hierarchy of QObject instances

25. They can have connections to other QObject instances

26. Example: does it make sense to copy a widget at run-time? “ QObject instances are individuals!”

28. Every QObject has a meta object

30. inheritance ( QObject::inherits )

31. properties

32. signals and slots

33. general information ( QObject::classInfo )

35. When a parent object is deleted, it deletes its children QObject *parent = new QObject(); QObject *child1 = new QObject(parent); QObject *child2 = new QObject(parent); QObject *child1_1 = new QObject(child1); QObject *child1_2 = new QObject(child1); delete parent;

38. Allocate parent on the stack void Widget::showDialog() { Dialog dialog; if (dialog.exec() == QDialog::Accepted) { ... } } Dialog::Dialog(QWidget *parent) : QDialog(parent) { QGroupBox *box = QGroupBox(this); QPushButton *button = QPushButton(this); QRadioButton *option1 = QRadioButton(box); QRadioButton *option2 = QRadioButton(box); ...

40. Heap memory must be explicitly freed using delete to avoid memory leaks.

41. Objects allocated on the heap can live for as long as they are needed. new delete Construction Destruction

43. Stack variables are automatically destructed when they go out of scope.

44. Objects allocated on the stack are always destructed when they go out of scope. int a } Construction Destruction

47. What makes Qt tick

48. Signals and Slots in Action emit clicked();

49. Signals and Slots in Action private slots: void on_addButton_clicked(); void on_deleteButton_clicked(); connect(clearButton,SIGNAL(clicked()),listWidget,SLOT(clear())); connect(addButton,SIGNAL(clicked()),this,SLOT(...)); 2x clear();

50. Signals and Slots in Action { ... emit clicked(); ... } { ... emit clicked(); ... } { ... emit clicked(); ... } { QString newText = QInputDialog::getText(this, &quot;Enter text&quot;, &quot;Text:&quot;); if( !newText.isEmpty() ) ui->listWidget->addItem(newText); } { foreach (QListWidgetItem *item, ui->listWidget->selectedItems()) { delete item; } } clear();

52. A slot can return values, but not through connections

53. Any number of signals can be connected to a slot

54. It is implemented as an ordinary method

55. It can be called as an ordinary method public slots: void aPublicSlot(); protected slots: void aProtectedSlot(); private slots: void aPrivateSlot(); connect(src, SIGNAL(sig()), dest, SLOT(slt()));

57. A signal always returns void

59. Usually results in a direct call, but can be passed as events between threads, or even over sockets (using 3 rd party classes)

60. The slots are activated in arbitrary order

61. A signal is emitted using the emit keyword signals: void aSignal(); emit aSignal();

62. Making the connection QObject::connect( src, SIGNAL( signature ), dest, SLOT( signature ) ); <function name> ( <arg type>... ) clicked() toggled(bool) setText(QString) textChanged(QString) rangeChanged(int,int) setTitle(QString text) setValue(42) A signature consists of the function name and argument types. No variable names, nor values are allowed. Custom types reduces reusability. setItem(ItemClass)

65. Triggered by calling QMetaObject::connectSlotsByName

69. Dialogs

70. Menus, toolbars, statusbars

71. Basic file management Open, Save and Save As We will run out of time!

72. Goal of the day

74. Use the QtCore and QtGui modules

75. Base the skeleton project on a QMainWindow

77. mainwindow.ui – the user interface of the main window

78. mainwindow.h/cpp – the class declaration and implementation of the main window

79. main.cpp – the main function, getting everything initialized and running

81. Features will be added to the application, while maintaining a functioning application through-out the process

82. This is how most software is being built in real life!

87. For each of these user actions, a QAction object will be created

89. Do not forget tooltips, statusbar tips, etc. Ctrl+S Action

92. icon – icon to be used everywhere

93. shortcut – shortcut

94. checkable / checked – if the action is checkable and the current check status

95. toolTip / statusTip – tips text for tool tips (hover and wait) and status bar tips (hover, no wait)

96. Why QAction QAction *action = new QAction( parent ); action->setText(&quot;text&quot;); action->setIcon(QIcon(&quot;:/icons/icon.png&quot;)); action->setShortcut(QKeySequence(&quot;Ctrl+G&quot;)); action->setData(myDataQVariant); Setting properties for text, icon and keyboard short-cut Creating a new action A QVariant can be associated with each action, to carry data associated with the given operation

99. Action icons can be added either from files or resources

101. No need to trying to determine the path for the icons for each specific install type

102. All fits neatly into the build system

103. ...

104. You can add anything into resources, not only icons

106. When having added the resource file, make sure to close any Designer forms and re-open them for Designer to discover the resource

108. Before any resources can be added to the resource file, you must first create a directory in the resource file

109. In this case we put icons into the /icons directory

111. Click “...” next to the icon setting

114. To add them to the toolbar, simply drag and drop

118. Slots are generated on the fly in both header and implementation

119. Implementing the new slot is easy – just create a new MainWindow and show it void MainWindow::on_actionNew_triggered() { MainWindow *w = new MainWindow(); w->show(); }

120. Closing and Exiting MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui->setupUi(this); setAttribute(Qt::WA_DeleteOnClose); connect(ui->actionClose, SIGNAL(triggered()), this, SLOT(close())); connect(ui->actionExit, SIGNAL(triggered()), qApp, SLOT(closeAllWindows())); } Setting the WA_DeleteOnClose attribute makes the widget delete itself when it is closed All widgets has a close slot out-of-the-box The QApplication class has a slot for closing all windows The qApp pointer refers to the current QApplication instance

122. New windows can be created

123. Windows can be closed

124. The application can exit (i.e. close all windows)

126. The expected behavior would be to ask the user before close a modified document

127. To implement this, we add a modified flag which is set whenever the text of the QTextEdit is changed

128. We also intercept close events and ask the user before closing modified events

133. QWidget provides virtual methods for the most common events, e.g. QWidget::closeEvent

136. question dialogs

137. information dialogs

138. warning dialogs

139. critical dialogs

140. about dialogs for both the current application and Qt itself Roughly the same type of dialogs with a title, a message and one or more buttons. The green words are function names for static members. To show an information dialog, use QMessageBox::information , etc.

141. QMessageBox QMessageBox::warning(this, &quot;Document Modified&quot;, &quot;The document has been modified, do you want to close it?&quot; &quot;You will lose all your changes.&quot;, QMessageBox::Yes | QMessageBox::No, QMessageBox::No) == QMessageBox::Yes Parent window Dialog title The message of the dialog. Notice the use of ' ' The buttons to use. Pick from Ok , Open , Save , Cancel , Close , Discard , Apply , Reset , Restore defaults , Help , Save all , Yes , Yes to all , No , No to all , Abort , Retry and Ignore The default button The return value is the button used for closing the dialog

143. By setting a window title with the sub-string “ [*] ”, the modified indication can be activated using setWindowModified . void MainWindow::updateWindowTitle() { setWindowTitle(tr(&quot;%1 [*] &quot;).arg(qApp->applicationName())); setWindowModified(m_modified); } This function is called from the constructor as well as from the documentModified slot

145. The QApplication object keeps track of the application's name, version, producer, etc.

146. This is used for window titles, etcetera a.setApplicationName(&quot;Text Editor&quot;); a.setApplicationVersion(&quot;0.1&quot;); a.setOrganizationName(&quot;ExampleSoft&quot;); a.setOrganizationDomain(&quot;example.com&quot;); a.setWindowIcon(QIcon(&quot;:/icons/new.png&quot;)); Application icon Producer name and domain Application name and version

148. New windows can be created

149. Windows can be closed

150. The application can exit (i.e. close all windows)

151. We can keep track of document modifications

152. A window cannot be closed without accepting the loss of document modifications

154. We add an action, add a View menu and put the action in the menu Text Name Icon Short-cut Tool-tip Select Font... actionSelectFont Select the display font New menus are always placed to the right, but they can be dragged in to place afterwards

157. The user expects settings to stick, i.e. use the last value when opening new windows

159. By using a QSettings object, you get a cross platform interface for handing settings

160. Any QVariant can be stored – but think about readability for advanced users QSettings settings; myString = settings.value(&quot;key&quot;,&quot;default&quot;).toString(); settings.setValue(&quot;key&quot;, myString); settings.remove(&quot;key&quot;);

162. Restoring the font void MainWindow::on_actionSelectFont_triggered() { bool ok; QFont font = QFontDialog::getFont(&ok, ui->textEdit->font(), this); if(ok) { QSettings settings; settings.setValue(&quot;viewFont&quot;, font); ui->textEdit->setFont(font); } } MainWindow::MainWindow(QWidget *parent) : ... { ... QSettings settings; ui->textEdit->setFont( settings.value(&quot;viewFont&quot;, QApplication::font()).value<QFont>()); ... Default value

163. Custom fonts!

165. New windows can be created

166. Windows can be closed

167. The application can exit (i.e. close all windows)

168. We can keep track of document modifications

169. A window cannot be closed without accepting the loss of document modifications

170. User configurable fonts

171. Persistent user settings

173. The actions are added to both the tool bar and menu Right click on the tool bar to add separators Text Name Icon Short-cut Tool-tip Cut actionCut Ctrl+X Cut Copy actionCopy Ctrl+C Copy Paste actionPaste Ctrl+V Paste

175. To avoid trying to copy in vain, let's add connections for enabling and disabling the actions depending on the selection connect(ui->actionCut, SIGNAL(triggered()), ui->textEdit, SLOT(cut())); connect(ui->actionCopy, SIGNAL(triggered()), ui->textEdit, SLOT(copy())); connect(ui->actionPaste, SIGNAL(triggered()), ui->textEdit, SLOT(paste())); connect(ui->textEdit, SIGNAL(copyAvailable(bool)), ui->actionCut, SLOT(setEnabled(bool))); connect(ui->textEdit, SIGNAL(copyAvailable(bool)), ui->actionCopy, SLOT(setEnabled(bool)));

178. New windows can be created

179. Windows can be closed

180. The application can exit (i.e. close all windows)

181. We can keep track of document modifications

182. A window cannot be closed without accepting the loss of document modifications

183. User configurable fonts

184. Persistent user settings

185. The expected clipboard actions: cut, copy and paste

186. Undo and redo

189. When a document is loaded

192. Loading

193. Saving QFile file(m_fileName); if(!file.open(QIODevice::WriteOnly | QIODevice::Text)) qFatal(&quot;Error opening file for writing&quot;); QTextStream out(&file); out << textString; QFile file(m_fileName); if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) qFatal(&quot;Error opening file for reading&quot;); QTextStream in(&file); in >> textString;

195. As a start, it is set in the constructor MainWindow::MainWindow( const QString &fileName , QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow), m_modified(false), m_fileName(fileName) { ... if(!m_fileName.isNull()) loadFile(); updateWindowTitle(); } The name can be QString() , i.e. null, as new, unnamed documents needs this

198. testing.txt - Text Editor void MainWindow::updateWindowTitle() { setWindowTitle(tr(&quot;%1[*] - %2&quot;) .arg(m_fileName.isNull()?&quot;untitled&quot;:QFileInfo(m_fileName).fileName()) .arg(QApplication::applicationName())); setWindowModified(m_modified); } Extracts the file name part of a file name with a path

200. It attempts to load the current file

201. If it fails, it sets the current filename to null void MainWindow::loadFile() { QFile file(m_fileName); if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) { QMessageBox::warning(this, QApplication::applicationName(), tr(&quot;Could not open file %1.%2&quot;) .arg(QFileInfo(m_fileName).fileName()) .arg(file.errorString())); m_fileName = QString(); } else { QTextStream in(&file); ui->textEdit->setText(in.readAll()); } m_modified = false; updateWindowTitle(); }

203. It attempts to load the current file

204. If it fails, it sets the current filename to null void MainWindow::loadFile() { QFile file(m_fileName); if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) { QMessageBox::warning(this, QApplication::applicationName(), tr(&quot;Could not open file %1.%2&quot;) .arg(QFileInfo(m_fileName).fileName()) .arg(file.errorString())); m_fileName = QString(); } else { QTextStream in(&file); ui->textEdit->setText(in.readAll()); } m_modified = false; updateWindowTitle(); }

206. It attempts to load the current file

207. If it fails, it sets the current filename to null void MainWindow::loadFile() { QFile file(m_fileName); if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) { QMessageBox::warning(this, QApplication::applicationName(), tr(&quot;Could not open file %1.%2&quot;) .arg(QFileInfo(m_fileName).fileName()) .arg(file.errorString())); m_fileName = QString(); } else { QTextStream in(&file); ui->textEdit->setText(in.readAll()); } m_modified = false; updateWindowTitle(); }

209. It attempts to load the current file

210. If it fails, it sets the current filename to null void MainWindow::loadFile() { QFile file(m_fileName); if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) { QMessageBox::warning(this, QApplication::applicationName(), tr(&quot;Could not open file %1.%2&quot;) .arg(QFileInfo(m_fileName).fileName()) .arg(file.errorString())); m_fileName = QString(); } else { QTextStream in(&file); ui->textEdit->setText(in.readAll()); } m_modified = false; updateWindowTitle(); }

213. The actions are added to the File menu and tool bar Text Name Icon Short-cut Tool-tip Open... actionOpen Ctrl+O Open a document Save actionSave Ctrl+S Save the current document Save As... actionSaveAs Ctrl+Shift+S Save current document as

218. Save As sets a name and attempts to save

219. Save is one of the options when a modified document is closed

220. Save As can be canceled

221. Saving can fail

222. Saving documents bool MainWindow::saveFile() { if(m_fileName.isNull()) return saveFileAs(); QFile file(m_fileName); if(!file.open(QIODevice::WriteOnly | QIODevice::Text)) { QMessageBox::warning(...); m_fileName = QString(); updateWindowTitle(); return false; } QTextStream out(&file); out << ui->textEdit->toPlainText(); m_modified = false; updateWindowTitle(); return true; } If the name is null, we need to save as Save the document If the file cannot be opened for writing, we display a warning and set the file name to null Update the modified flag and title Return true on success

223. Saving documents bool MainWindow::saveFileAs() { QString fileName = QFileDialog::getSaveFileName(...); if(!fileName.isNull()) { m_fileName = fileName; return saveFile(); } return false; } Ask the user for a file name If a name is given, attempt to save If no name is given, the save is a failure The method saveFileAs never calls saveFile unlese !fileName.isNull() thus there is no risk for infinite recursion

226. Saving documents void MainWindow::closeEvent(QCloseEvent *e) { if(m_modified) { switch(QMessageBox::warning(this, &quot;Document Modified&quot;, &quot;The document has ...&quot;, QMessageBox::Yes | QMessageBox::No | QMessageBox::Cancel, QMessageBox::Cancel)) { case QMessageBox::Yes: if(saveFile()) e->accept(); else e->ignore(); break; case QMessageBox::No: e->accept(); break; case QMessageBox::Cancel: e->ignore(); break; } } else { e->accept(); } } The user wants to save The user do not want to save Cancel the closing Close unmodified documents Depending on the save, close or ignore

228. New windows can be created

229. Windows can be closed

230. The application can exit (i.e. close all windows)

231. We can keep track of document modifications

232. A window cannot be closed without accepting the loss of document modifications

233. User configurable fonts

234. Persistent user settings

235. The expected clipboard actions: cut, copy and paste

236. Undo and redo

237. Can load documents

238. Can save documents

239. Thank you for your attention! [email_address]