![#include <QGuiApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
main.cpp
14](https://image.slidesharecdn.com/qtforbeginnersp11-171029113053/85/Qt-for-beginners-12-320.jpg)
![Using Containers
Using QList
QList<QString> list;
list << "one" << "two" << "three";
QString item1 = list[1]; // "two"
for(int i = 0; i < list.count(); i++) {
const QString &item2 = list.at(i);
}
int index = list.indexOf("two"); // returns 1
Using QMap
QMap<QString, int> map;
map["Norway"] = 5; map["Italy"] = 48;
int val = map["France"]; // inserts key if not exists
if (map.contains("Norway")) {
int val2 = map.value("Norway"); // recommended lookup
}
28](https://image.slidesharecdn.com/qtforbeginnersp11-171029113053/85/Qt-for-beginners-26-320.jpg)
![Connection Variants
Using macros (traditional method):
connect(slider, SIGNAL(valueChanged(int)),
spinbox, SLOT(setValue(int)));
Using member functions:
connect(slider, &QSlider::valueChanged,
spinbox, &QSpinBox::setValue);
Using non-member functions:
static void printValue(int value) {...}
connect(slider, &QSlider::valueChanged, &printValue);
Using C++11 lambda functions:
connect(slider, &QSlider::valueChanged,
[=] (int value) {...});
49](https://image.slidesharecdn.com/qtforbeginnersp11-171029113053/85/Qt-for-beginners-47-320.jpg)
Qt for beginners
- 1. Qt For Beginners - Part 1 Overview and Key Concepts Sergio Shevchenko eTuitus S.r.l. 1
- 2. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 2
- 3. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 3
- 4. Why Qt? ✓Write code once to target multiple platforms (“Write Once, Compile Anywhere”) ✓Produce compact, high-performance applications ✓Focus on innovation, not infrastructure coding ✓Count on professional services, support and training ✓Take part in an active Qt ecosystem 4
- 5. What is Qt? 5 Qt (/kjuːt/ "cute") is a cross-platform application framework that is widely used for developing application software that can be run on various software and hardware platforms with little or no change in the underlying codebase, while still being a native application with the capabilities and speed thereof.
- 6. Widgets versus QML Widgets: Originally designed for desktop Mouse and keyboard navigation Can be used for embedded, incl. touchscreen Stable Qt Quick/QML: Primarily designed for mobile/embedded Touchscreen navigation Declarative programming language QML backed by JavaScript Can be used for desktop too! 8
- 7. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 9
- 8. How Much C++ Do You Need To Know? Objects and classes Declaring a class, inheritance, calling member functions etc. Polymorphism Virtual methods Operator overloading Templates Limited to the container and concurrent classes No... ...RTTI ...Sophisticated templates ...Exceptions ...C++11/C++14 10
- 9. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 11
- 11. // Simple QML example import QtQuick 2.6 Rectangle { width: 200 height: 200 Text { anchors.centerIn: parent font.pixelSize: 18 text: "Hello, world!" } MouseArea { anchors.fill: parent onClicked: { Qt.quit() } } } main.qml 13
- 12. #include <QGuiApplication> #include <QQmlApplicationEngine> int main(int argc, char *argv[]) { QGuiApplication app(argc, argv); QQmlApplicationEngine engine; engine.load(QUrl(QStringLiteral("qrc:/main.qml"))); return app.exec(); } main.cpp 14
- 13. Example testproject.pro TEMPLATE = app # app is default - could be 'subdirs' or 'lib' TARGET = testproject # executable or library name QT += qml quick # Qt modules to use CONFIG += debug c++11 # release is default SOURCES += main.cpp # source files RESOURCES += qml.qrc # resource files 15
- 14. Using qmake qmake tool Generates a Makefile or Visual Studio project Build project using qmake cd testProject qmake testProject.pro # creates Makefile make # compiles and links application ./testProject # executes application Tip: qmake -project Creates default project file based on directory content You can run qmake from a different directory to set up shadow build. Qt Creator does it all for you 16
- 15. 17
- 16. Qt Assistant Standalone help browser Reference Documentation All classes documented Contains tons of examples Collection of Howtos and Overviews 18
- 18. Modules 20 Qt Modules Qt Essentials: includes QtCore, QtGui, QtWidgets, QtQml, QtQuick, QtSql, QtNetwork, QtTest, QtMultimedia, QtQuickControls, etc. Add-on Modules included with Qt 5.6: QtBlueTooth, QtDbus, QtLocation, QtPositioning, QtSvg, QtUiTools, QtWebEngineCore, QtWebSockets, QtXml, QtXmlPatterns, etc. Modules contain libraries, plugins, and documentation Enable Qt Modules in qmake .pro file: QT += widgets xml sql dbus multimedia network Default: qmake projects use QtCore and QtGui QWidget based projects require QtWidgets module QtQuick2 projects require QtQuick and QtQml modules
- 19. Every Qt class has a header file. #include <QApplication> #include <QGuiApplication> #include <QCoreApplication> #include <QString> #include <QColor> #include <QWidget> Every Qt Module has a header file. #include <QtCore> #include <QtGui> #include <QtWidgets> #include <QtMultimedia> #include <QtSql> #include <QtConcurrent> Many modules have a corresponding Qt class. Module headers include all of the classes in that module. 21 More Include Files
- 20. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 22
- 21. Text Processing with QString Strings can be created in a number of ways Conversion constructor and assignment operators: QString str("abc"); str = "def"; Create a numerical string using a static function: QString n = QString::number(1234); From a char pointer using the static functions: QString text = QString::fromLatin1("Hello Qt"); QString text = QString::fromUtf8(inputText); QString text = QString::fromLocal8Bit(cmdLineInput); QString text = QStringLiteral("Literal string"); // UTF-8 From char pointer with translations: QString text = tr("Hello Qt"); 23
- 22. Text Processing with QString QString str = str1 + str2; fileName += ".txt"; simplified() // removes duplicate whitespace left(), mid(), right() // part of a string leftJustified(), rightJustified() // padded version length(), endsWith(), startsWith() contains(), count(), indexOf(), lastIndexOf() toInt(), toDouble(), toLatin1(), toUtf8(), toLocal8Bit() 24
- 23. Formatted Output With QString::arg() int i = ...; int total = ...; QString fileName = ...; QString status = tr("Processing file %1 of %2: %3") .arg(i).arg(total).arg(fileName); double d = 12.34; QString str = QString::fromLatin1("delta: %1").arg(d,0,'E',3) // str == "delta: 1.234E+01"; Convenience: arg(QString,...,QString) (“multi-arg”). Only works with all QString arguments. 25
- 24. Text Processing With QStringList QString::split(), QStringList::join() QStringList::replaceInStrings() QStringList::filter() 26
- 25. Container Classes General purpose template-based container classes QList<QString> - Sequence Container Other: QLinkedList, QVector, QStack, QQueue QMap<int, QString> - Associative Container Other: QHash, QSet, QMultiMap, QMultiHash Qt's Container Classes compared to STL: Lighter, safer, and easier to use than STL containers If you prefer STL, feel free to... well.. whatever :-) Methods exist that convert between Qt and STL E.g. you need to pass std::list to a Qt method 27
- 26. Using Containers Using QList QList<QString> list; list << "one" << "two" << "three"; QString item1 = list[1]; // "two" for(int i = 0; i < list.count(); i++) { const QString &item2 = list.at(i); } int index = list.indexOf("two"); // returns 1 Using QMap QMap<QString, int> map; map["Norway"] = 5; map["Italy"] = 48; int val = map["France"]; // inserts key if not exists if (map.contains("Norway")) { int val2 = map.value("Norway"); // recommended lookup } 28
- 27. Algorithm Complexity Concern: How fast a function is as a container grows Sequential Container Associative Container All complexities are amortized 29 Lookup Insert Append Prepend QList O(1) O(n) O(1) O(1) QVector O(1) O(n) O(1) O(n) QLinkedList O(n) O(1) O(1) O(1) Lookup Insert QMap O(log(n)) O(log(n)) QHash O(1) O(1)
- 28. Iterators Allow reading a container's content sequentially Java-style iterators: simple and easy to use QListIterator<...> for read QMutableListIterator<...> for read-write STL-style iterators slightly more efficient QList::const_iterator for read QList::iteratorfor read-write Same works for QSet, QMap, QHash, ... 30
- 29. Iterators Java Style Example QList iterator QList<QString> list; list << "A" << "B" << "C" << "D"; QListIterator<QString> it(list); Forward iteration while (it.hasNext()) { qDebug() << it.next(); // A B C D } Backward iteration it.toBack(); // position after the last item while (it.hasPrevious()) { qDebug() << it.previous(); // D C B A } 31
- 30. STL-Style Iterators Example QList iterator QList<QString> list; list << "A" << "B" << "C" << "D"; QList<QString>::iterator i; Forward mutable iteration for (i = list.begin(); i != list.end(); ++i) { *i = (*i).toLower(); } Backward mutable iteration i = list.end(); while (i != list.begin()) { --i; *i = (*i).toLower(); } QList<QString>::const_iterator for read-only 32
- 31. The foreach Keyword It is a macro, feels like a keyword foreach (const QString &str, list) { if (str.isEmpty()) break; qDebug() << str; } break and continue as normal Modifying the container while iterating Results in container being copied Iteration continues in unmodified version Not possible to modify item Iterator variable is a const reference. C++11 expands the for keyword for iteration over containers. C++11 auto feature can also be useful for iterators to infer the appropriate type. 33
- 32. Implicit Sharing and Containers Implicit Sharing If an object is copied, then its data is copied only when the data of one of the objects is changed ("copy on write") Shared class has a pointer to shared data block Shared data block = reference counter and actual data Assignment is a shallow copy Changing results into deep copy (detach) QList<int> list1, list2; list1 << 1 << 2; list2 = list1; // shallow-copy: shares data with list1 list2 << 3; // deep-copy: change triggers detach 34
- 33. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 35
- 34. Qt's C++ Object Model - QObject QObject is the heart of Qt's object model Include these features: Memory management Object properties Introspection Signals and Slots QObject has no visual representation 36
- 35. Object Trees 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 Construction/Destruction Trees can be constructed in any order Trees can be destroyed in any order If object has a parent: object is first removed from the parent If object has children: deletes each child first No object is deleted twice Note: Parent-child relationship is not inheritance! 37
- 36. Creating Objects - General Guidelines On Heap - QObject with parent QTimer *timer = new QTimer(this); On Stack - QObject without parent: QFile, usually local to a function QApplication (local to main()) QSettings, lightweight to create, local to a function On Stack - value types QString, QList, QHash, QMap, QColor, QImage, QPixmap, QVariant Stack or Heap - QDialog - depending on lifetime 38
- 37. QVariant QVariant Union for common Qt "value types" (copyable, assignable) Supports implicit sharing (fast copying) Supports user types A generic data object Use cases: QVariant property(const char *name) const; void setProperty(const char *name, const QVariant &value); class QAbstractItemModel { virtual QVariant data(const QModelIndex &index, int role); … }; 39
- 38. QVariant For QtCore types QVariant variant(42); int value = variant.toInt(); // read back as integer QString text = variant.toString(); // read back as string qDebug() << variant.typeName(); // int For non-core and custom types: QVariant variant = QVariant::fromValue(QColor(Qt::red)); QColor color = variant.value<QColor>(); // read back qDebug() << variant.typeName(); // "QColor" 40
- 39. Callbacks General Problem: How do you get from "the user clicks a button" to your business logic? Possible solutions Callbacks Based on function pointers Traditionally 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. 41
- 40. Signal Slot diagram 42 QObject::connect(X, Signal1, Y, SlotA); QObject::connect(Y, Signal1, X, SlotA); QObject::connect(Z, Signal1, Y, SlotB); QObject::connect(Z, Signal1, X, SlotA); QObject::connect(Z, Signal2, X, SlotB);
- 41. Custom Slots File: myclass.h class MyClass : public QObject { Q_OBJECT // marker for moc // … public slots: void setValue(int value); // a custom slot }; File: myclass.cpp void MyClass::setValue(int value) { // slot implementation } 43
- 42. Custom Signals File: myclass.h class MyClass : public QObject { Q_OBJECT // marker for moc // … signals: void valueChanged(int value); // a custom signal }; File: myclass.cpp // No implementation for a signal! Sending a signal emit valueChanged(value); 44
- 43. // Slider.qml Rectangle { id: container ... signal valueChanged(var v) ... MouseArea { anchors.fill: parent ... onPositionChanged: { currentValue = factor * slide.x container.valueChanged(currentValue) } } ... ... Signal Emitted Connecting Signals to Slots 45
- 44. // Spinner.qml signal valueChanged(var v) ... function setValue(newValue) { if (newValue !== view.currentIndex) { view.currentIndex = newValue } } ... Slot/Method Implemented 46 Connecting Signals to Slots
- 45. QObject::connect(sliderItem, SIGNAL(valueChanged(QVariant)), pickerItem, SLOT(setValue(QVariant))); In C++ Code: Signal/Slot Connection Established Connecting Signals to Slots 47
- 46. Connections { target: slider onValueChanged: { picker.setValue(slider.value) } } In QML Code: Signal/Slot Connection Established Connecting Signals to Slots 48
- 47. Connection Variants Using macros (traditional method): connect(slider, SIGNAL(valueChanged(int)), spinbox, SLOT(setValue(int))); Using member functions: connect(slider, &QSlider::valueChanged, spinbox, &QSpinBox::setValue); Using non-member functions: static void printValue(int value) {...} connect(slider, &QSlider::valueChanged, &printValue); Using C++11 lambda functions: connect(slider, &QSlider::valueChanged, [=] (int value) {...}); 49
- 48. Variations of Signal/Slot Connections Signal to Signal connection connect(bt, SIGNAL(clicked()), this, SIGNAL(okSignal())); Not allowed to name parameters connect(m_slider,SIGNAL(valueChanged(int value)), this, SLOT(setValue(int newValue))) 50
- 49. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 51
- 50. A Look Ahead Qt For Beginners Part 2 - QML and Qt Quick Qt For Beginners Part 3 - Doing More with mobile 52
- 51. Agenda Features of Qt C++ Refresher Hello World Application Core Classes Objects and Object Communication A Look Ahead Q&A 53