1. -1- National Alliance for Medical Image Computing First Steps with Qt Julien Finet Kitware Inc. Jan. 05 th 2010

2. -2- National Alliance for Medical Image Computing Hello World! #include int main(int argc, char * argv[]) { QApplication app(argc, argv); QPushButton button(“Hello World”); button.show(); return app.exec(); } The QApplication object must be created before any GUI-related features of Qt are used. Enter the loop of events. Qt receives and processes user and system events and passes these on to the appropriate widgets.

3. -3- National Alliance for Medical Image Computing Qt classes QObject QWidget QLabelQAbstractButton QPushButtonQCheckBox QAction QPaintDevice … …

4. -4- National Alliance for Medical Image Computing QObjects The QObject class is the base class of all Qt objects When deleted, the parent deletes its children. class QObject { public: QObject(QObject * parent = 0); virtual ~QObject(); const QObjectList & children () const; void setParent(QObject * parent); }; Add itself to the parent’s children list. qobject.h

5. -5- National Alliance for Medical Image Computing QWidgets If a widget’s parent is 0, the widget is a window. When shown/hidden, the parent shows/hides its children. When enabled/disabled, the parent enables/disables its children (except for children explicitly hidden).

6. -6- National Alliance for Medical Image Computing QObjects QObjects can be safely created on the heap. Be careful when instantiating on the stack. … int main(int argc, char* argv[]) { … QWidget parentWidget; QPushButton* button = new QPushButton(“Hello World”, parentWidget); … } parentWidget’s destructor deletes button int main(int argc, char* argv[]) { … QWidget parentWidget; QPushButton button(“Hello World”, & parentWidget); … } int main(int argc, char* argv[]) { … QPushButton button(“Hello World”); QWidget parentWidget; button.setParent(&parentWidget); … } Error: button is deleted twice The destructor of button is called first, and it removes itself from its parent.

7. -7- National Alliance for Medical Image Computing Non QObject May be instantiated on the heap or stack. It’s safer to create them on the stack. … QVector * ages; … ages = new QVector (10); … delete ages; … QString firstName(“John”); QString lastName(“Doe”); Qvector ages; … ages.resize(10); …

8. -8- National Alliance for Medical Image Computing QLayout – Geometry Manager Instead of specifying widget coordinates for each QWidget, use QLayouts. … QGroupBox* parameters = new QGroupBox(“Parameters”, this); QLabel* label = new QLabel(“Number of Iterations:”, parameters); QSpinBox* spinBox = new QSpinBox(parameters); … label->setGeometry(0, 0, 50, 20); spinBox->setGeometry(56, 0, 30, 20); … QGroupBox* parameters = new QGroupBox(“Parameters, this); QLabel* label = new QLabel(“Number of Iterations:”, parameters); QSpinBox* spinBox = new QSpinBox(parameters); … QHBoxLayout* layout = new QHBoxLayout; layout->addWidget(label); layout->addWidget(spinBox); parameters->setLayout(layout); … Without QLayoutWith QLayout

9. -9- National Alliance for Medical Image Computing QLayout class diagram QObject QLayout QStackedLayo ut QBoxLayout QVBoxLayoutQHBoxLayout QGridLayoutQFormLayout

10. -10- National Alliance for Medical Image Computing QLayout Example 1/2 QHBoxLayout QVBoxLayout … QHBoxLayout* layout = new QHBoxLayout; layout>addWidget(iterationNumberLabel); layout->addWidget(iterationNumberSpinBox); layout->addWidget(thresholdLabel); layout->addWidget(thresholdDoubleSpinBox); parameters->setLayout(layout); … QVBoxLayout* layout = new QVBoxLayout; layout>addWidget(iterationNumberLabel); layout->addWidget(iterationNumberSpinBox); layout->addWidget(thresholdLabel); layout->addWidget(thresholdDoubleSpinBox); parameters->setLayout(layout); …

11. -11- National Alliance for Medical Image Computing Qlayout Example 2/2 QGridLayout QFormLayout QGridLayout* layout = new QGridLayout; layout>addWidget(iterationNumberLabel, 0, 0, 1, 1); layout->addWidget(iterationNumberSpinBox, 0, 1, 1, 1); layout->addWidget(thresholdLabel, 1, 0, 1, 1); layout->addWidget(thresholdDoubleSpinBox, 1, 1, 1, 1); parameters->setLayout(layout); … QFormLayout* layout = new QFormLayout; layout>setWidget(0, QFormLayout::LabelRole, iterationNumberLabel); layout->setWidget(0, QFormLayout::FieldRole, iterationNumberSpinBox); layout->setWidget(1, QFormLayout::LabelRole, thresholdLabel); layout->addWidget(1, QFormLayout::FieldRole, thresholdDoubleSpinBox); parameters->setLayout(layout); …

12. -12- National Alliance for Medical Image Computing Signals & Slots Qt uses signals and slots for high-level events (listerners) and virtual methods for low-level events Type-safe callbacks Precompiler (moc) A class which emits a signal neither knows nor cares which slots receive the signal

13. -13- National Alliance for Medical Image Computing Signals & Slots

14. -14- National Alliance for Medical Image Computing Signals & Slots - Example... class QSlider: public QWidget { Q_OBJECT public: … public slots: void setValue(int value); … signals: void valueChanged(int value); … }; … void QSlider::setValue(int value) { … if (value != old) { emit valueChanged(value); } } … valueChanged() is not defined … int main(…) { … QSpinBox* spinBox = new QSpinBox(panel); QSlider* slider = new QSlider(panel); … QObject::connect(slider, SIGNAL(valueChanged(int)), spinBox, SLOT(setValue (int))); QObject::connect(spinBox, SIGNAL(valueChanged(int)), slider, SLOT(setValue (int))); … }... class QSpinBox: public QWidget { Q_OBJECT public: … public slots: void setValue(int value); … signals: void valueChanged(int value); … }; … void QSlider::setValue(int value) { … if (value != old) { emit valueChanged(value); } } … QSpinBox.h QSpinBox.cpp

15. -15- National Alliance for Medical Image Computing Signals & Slots - Example PROJECT(MyProject) FIND_PACKAGE(Qt4 REQUIRED) INCLUDE(${QT_USE_FILE}) SET(MyProject_SRCS MyWidget.cxx main.cxx) SET(MyProject_MOC_SRCS MyWidget.h) QT4_WRAP_CPP(MyProject_SRCS ${MyProject_MOC_SRCS}) ADD_EXECUTABLE( MyProject ${MyProject_SRCS}) TARGET_LINK_LIBRARIES(MyProject ${QT_LIBRARIES}) #include class MyWidget: public QWidget { Q_OBJECT public: MyWidget(QWidget* parent = 0); public slots: void setValue(int value); signals: void valueChanged(int value); private: int Value; }; #include “MyWidget.h” void MyWidget::MyWidget(QWidget* parent) : QWidget(parent) { } void MyWidget::setValue(int value) { if (value != this->Value) { value = this->Value; emit this->valueChanged(this->Value); } } MyWidget.h MyWidget.cxx CMakeLists.cxx #include #include “MyWidget.h” int maint(int argc, char* argv[]) { QApplication app(argc, argv); QGroupBox container; MyWidget w1(&container); MyWidget w2(&container); QObject::connect(w1, SIGNAL(valueChanged(int)), w2, SLOT(setValue(int))); container.show(); return app.exec(); } main.cxx

16. -16- National Alliance for Medical Image Computing Signals & Slots – Good to remember 1 Every connection you make emits a signal – duplicate connections emit two signals. –break a connection using disconnect() You can connect a signal to a signal Signals can have default values _ … QObject::connect(loginPushbutton, SIGNAL(clicked()), this, SIGNAL(loginRequested())); … class MyWidget: public QObject { … signals: void mySignal(int value = 5); … }; … emit mySignal(); … emit mySignal(10); … QObject::connect(button, SIGNAL(clicked()), widget2, SLOT(updateScreen())); … QObject::connect(button, SIGNAL(clicked()), widget2, SLOT(updateScreen())); … MyWidget.h MyWidget.cxx

17. -17- National Alliance for Medical Image Computing Signals & Slots – Good to remember 2 Slots are implemented as normal methods –Slots can be virtual, public, protected, private. Slot may have a shorter signature than the signal it receives –slots can ignore extra arguments. class MyWidget: public QObject { … protected slots: virtual void myAbstractSlot() = 0; … }; … QObject::connect(pushButton, SIGNAL(clicked()), this, SLOT(myAbstractSlot())); … QObject::connect(slider, SIGNAL(valueChanged(int)), this, SLOT(update())); … MyWidget.h MyWidget.cxx

18. -18- National Alliance for Medical Image Computing Qt Designer

19. -19- National Alliance for Medical Image Computing QtDesigner- Example … SET(MyProject_UI_SRCS Resources/UI/MyProject.ui) … QT4_WRAP_UI(MyProject_UI_CXX ${MyProject_UI_SRCS}) … #include #include “ui_MyWidget.h” class MyWidget: public Qwidget, Ui_MyWidget { … }; #include “MyWidget.h” #include “"ui_MyWidget.h” void MyWidget::MyWidget(QWidget* parent) : QWidget(parent) { this->setupUi(this); } MyWidget.h MyWidget.cxx CMakeLists.cxx #include #include “MyWidget.h” int maint(int argc, char* argv[]) { QApplication app(argc, argv); MyWidget w(0); w.show(); return app.exec(); } main.cxx