[Previous: Chapter 5] [Qt Tutorial] [Next: Chapter 7] Qt Tutorial 6 - Building Blocks Galore!
Files: This example shows how to encapsulate two widgets into a new component and how easy it is to use many widgets. For the first time, we use a custom widget as a child widget. #include <QApplication> #include <QFont> #include <QGridLayout> #include <QLCDNumber> #include <QPushButton> #include <QSlider> #include <QVBoxLayout> #include <QWidget> class LCDRange : public QWidget { public: LCDRange(QWidget *parent = 0); }; LCDRange::LCDRange(QWidget *parent) : QWidget(parent) { QLCDNumber *lcd = new QLCDNumber(2); lcd->setSegmentStyle(QLCDNumber::Filled); QSlider *slider = new QSlider(Qt::Horizontal); slider->setRange(0, 99); slider->setValue(0); connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int))); QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(lcd); layout->addWidget(slider); setLayout(layout); } class MyWidget : public QWidget { public: MyWidget(QWidget *parent = 0); }; MyWidget::MyWidget(QWidget *parent) : QWidget(parent) { QPushButton *quit = new QPushButton(tr("Quit")); quit->setFont(QFont("Times", 18, QFont::Bold)); connect(quit, SIGNAL(clicked()), qApp, SLOT(quit())); QGridLayout *grid = new QGridLayout; for (int row = 0; row < 3; ++row) { for (int column = 0; column < 3; ++column) { LCDRange *lcdRange = new LCDRange; grid->addWidget(lcdRange, row, column); } } QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(quit); layout->addLayout(grid); setLayout(layout); } int main(int argc, char *argv[]) { QApplication app(argc, argv); MyWidget widget; widget.show(); return app.exec(); } Line by Line Walkthroughclass LCDRange : public QWidget { public: LCDRange(QWidget *parent = 0); }; The LCDRange widget is a widget without any API. It just has a constructor. This sort of widget is not very useful, so we'll add some API later. LCDRange::LCDRange(QWidget *parent) : QWidget(parent) { QLCDNumber *lcd = new QLCDNumber(2); lcd->setSegmentStyle(QLCDNumber::Filled); QSlider *slider = new QSlider(Qt::Horizontal); slider->setRange(0, 99); slider->setValue(0); connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int))); QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(lcd); layout->addWidget(slider); setLayout(layout); } This is lifted straight from the MyWidget constructor in Chapter 5. The only differences are that the Quit button is left out and the class is renamed. class MyWidget : public QWidget { public: MyWidget(QWidget *parent = 0); }; MyWidget, too, contains no API except a constructor. MyWidget::MyWidget(QWidget *parent) : QWidget(parent) { QPushButton *quit = new QPushButton(tr("Quit")); quit->setFont(QFont("Times", 18, QFont::Bold)); connect(quit, SIGNAL(clicked()), qApp, SLOT(quit())); The push button that used to be in what is now LCDRange has been separated so that we can have one Quit button and many LCDRange objects. QGridLayout *grid = new QGridLayout; We create a QWidget with a QGridLayout that will contain three columns. The QGridLayout automatically arranges its widgets in rows and columns; you can specify the row and column numbers when adding widgets to the layout, and QGridLayout will fit them into the grid. for (int row = 0; row < 3; ++row) { for (int column = 0; column < 3; ++column) { LCDRange *lcdRange = new LCDRange; grid->addWidget(lcdRange, row, column); } } We create nine LCDRange widgets, all of which are children of the grid object, and we arrange them in three rows and three columns. QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(quit); layout->addLayout(grid); setLayout(layout); } Finally, we add the Quit button and the grid layout containing LCDRange widgets, to the main layout. The QWidget::addLayout() function is similar to the QWidget::addWidget() function, making the given layout a child og the main layout. That's all. Running the ApplicationThis program shows how easy it is to use many widgets at a time. Each one behaves like the slider and LCD number in the previous chapter. Again, the difference lies in the implementation. ExercisesInitialize each slider with a different/random value on startup. [Previous: Chapter 5] [Qt Tutorial] [Next: Chapter 7]
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