- Qt 6.5
- Qt Charts
- Qt Charts Examples
- SelectedBar Example
- Qt Charts | Commercial or GPLv3

# SelectedBar Example

The example shows how to use a selection feature for the bar chart.

The example shows changing the color and state of bars using the selection feature.

#### Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

#### Using setBarSelected()

We create the sets and fill them with the data. Then we create a series and append data to it.

     QBarSet *setChicken = Utilities::createChickenSet();
     QBarSet *setPork = Utilities::createPorkSet();
     QBarSet *setTurkey = Utilities::createTurkeySet();
     QBarSet *setHam = Utilities::createHamSet();
     qreal totalSum = setChicken->sum() + setPork->sum() + setTurkey->sum() + setHam->sum();
     QList<QBarSet *> setList = QList<QBarSet *>{setChicken, setPork, setTurkey, setHam};

     QBarSeries *series = new QBarSeries();
     series->append(setList);

We create the chart and add series to it. Also, we add a title to the chart, set animation for the chart, and align the legend.

     QChart *chart = new QChart();
     chart->addSeries(series);
     chart->setTitle(QCoreApplication::tr("Meat consumption"));
     chart->setAnimationOptions(QChart::SeriesAnimations);
     chart->legend()->setVisible(true);
     chart->legend()->setAlignment(Qt::AlignBottom);

Here we set the color for the selected bars.

     for (QBarSet *barSet : series->barSets())
         barSet->setSelectedColor(barSet->brush().color().darker());

Next step is adding axes: QBarCategoryAxis for years of measurements and QValueAxis for values range.

     QStringList categories = Utilities::createYearCategories();
     QBarCategoryAxis *axisX = new QBarCategoryAxis();
     axisX->setCategories(categories);
     chart->addAxis(axisX, Qt::AlignBottom);
     series->attachAxis(axisX);

     QValueAxis *axisY = new QValueAxis();
     axisY->setRange(0, 20);
     axisY->setTitleText(QCoreApplication::tr("Tons"));
     axisY->setLabelsAngle(-90);
     axisY->setTitleVisible(true);
     chart->addAxis(axisY, Qt::AlignLeft);
     series->attachAxis(axisY);

Then we add the chart view to put the chart in.

     QChartView *chartView = new QChartView(chart);
     chartView->setRenderHint(QPainter::Antialiasing);

Here we create a widget for labels of values of selected and unselected bars.

     QWidget *labelWidget = new QWidget(&mainWindow);
     QHBoxLayout *labelLayout = new QHBoxLayout(labelWidget);
     labelLayout->setAlignment(Qt::AlignCenter);

     QLabel *totalSumLabel = new QLabel(QCoreApplication::tr("Total sum: %1 T").arg(totalSum));
     labelLayout->addWidget(totalSumLabel);
     totalSumLabel->setContentsMargins(0, 0, 54, 0);

     QLabel *selectedSumLabel = new QLabel(QCoreApplication::tr("Selected sum: 0 T"));
     labelLayout->addWidget(selectedSumLabel);

     QLabel *unselectedSumLabel = new QLabel(QCoreApplication::tr("Unselected sum: %1 T").arg(totalSum));
     labelLayout->addWidget(unselectedSumLabel);
     unselectedSumLabel->setContentsMargins(54, 0, 0, 0);

We connect selecting of a specific bar with labels of values using a lambda. `set->toggleSelection({index})` sets the bar selected.

     QObject::connect(series, &QAbstractBarSeries::clicked, series, [=](int index, QBarSet *set) {
         set->toggleSelection({index});
         qreal selectedSum = 0.;
         for (int i = 0; i < setList.size(); ++i) {
             auto selectedIndices = setList.at(i)->selectedBars();
             for (int k = 0; k < selectedIndices.size(); ++k)
                 selectedSum += setList.at(i)->at(selectedIndices.at(k));
         }
         selectedSumLabel->setText(QCoreApplication::tr("Selected sum: %1 T").arg(selectedSum));
         // Because of rounding errors, selectedSum can result in being bigger than total sum
         qreal unselectedSum = totalSum - selectedSum < 0 ? 0. : totalSum - selectedSum;
         unselectedSumLabel->setText(
                                     QCoreApplication::tr("Unselected sum: %1 T")
                                     .arg(unselectedSum)
                                    );
     });

Finally, we create the main widget and add other layouts to it and run the application.

     QWidget *mainWidget = new QWidget(&mainWindow);
     QVBoxLayout *mainLayout = new QVBoxLayout(mainWidget);

     mainLayout->addWidget(chartView);
     mainLayout->addWidget(labelWidget);

     mainWindow.setCentralWidget(mainWidget);
     mainWindow.resize(800, 600);

     mainWindow.show();
     return a.exec();

Example project @ code.qt.io