How do I auto zoom a chart in Qt when window size change?

Question

I create a chart with QChart & QGraphicsScene & QGraphicsView, but the chart does not auto zoom in or zoom out when window change. How could I do that? I don't there is any signal or slot in QChart, QGraphicsScene, or QGraphicsView class. I know I could use QChart & QChartView, but I want QChart & QGraphicsScene & QGraphicsView for some purpose. Here is my code for draw a chart:

void MainWindow::on_actionDraw_Sine_Chart_triggered()
{
    QSplineSeries *spline = new QSplineSeries;

    for (double x = -M_PI; x < M_PI; x += 0.01) {
        spline->append(x, sin(x));
    }

    spline->setName(tr("Sine Curve"));    
    QChart *chart = new QChart;
    chart->addSeries(spline);
    chart->createDefaultAxes();
    chart->axisX()->setRange(-4, 4);
    chart->axisY()->setRange(-1.2, 1.2);
    chart->setGeometry(ui->graphicsView->rect());

    QGraphicsScene *scene = new QGraphicsScene;
    scene->addItem(chart);
    ui->graphicsView->setScene(scene);
}

Complete code is available here.

score 0 · Accepted Answer · answered Apr 27 '18 at 17:14

You have to track the size change of the viewport and change the size of the QChart, for that we use eventFilter, but since it is another method you need that chart is an attribute of the class.

In addition to this it is not advisable to create the scene in the one slot, but in the constructor, the same with the QChart, and then only add the series.

*.h

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    ...
    bool eventFilter(QObject *watched, QEvent *event); // +++
private:
    Ui::MainWindow *ui;
    QChart *chart; // +++
    QGraphicsScene *scene; // +++
};

*.cpp

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    scene = new QGraphicsScene;
    chart = new QChart;
    scene->addItem(chart);
    ui->graphicsView->setScene(scene);
    ui->graphicsView->viewport()->installEventFilter(this);

}

void MainWindow::on_actionDraw_Sine_Chart_triggered(){
    QSplineSeries *spline = new QSplineSeries;

    for (double x = -M_PI; x < M_PI; x += 0.01) {
        spline->append(x, sin(x));
    }
    spline->setName(tr("Sine Curve"));
    chart->addSeries(spline);
}


bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if(watched == ui->graphicsView->viewport() && event->type() == QEvent::Resize){
        if(chart)
            chart->resize(ui->graphicsView->viewport()->size());
    }
    return QMainWindow::eventFilter(watched, event);
}

Thank you for your kindly reply. I don't know even filter quite well. I decided to keep it the old way. I'm considering maybe I could create QGraphicsView object for showing image, and create QChartView for showing charts later. — Darcy, May 07 '18 at 14:44

How do I auto zoom a chart in Qt when window size change?

1 Answers1