How to re(?: paint, display, draw, ...) or update graphicsview after updating



  • With a (derived object of) qchart in a (derived object of) qgraphicsview, how do you re(?: paint, display, draw) or update the chart after its series points are updated (what function of qchart or qgraphicsscene or qgraphicsview do you call for this task)? a sample code attached below.

    view.cpp:

    void View::updateChart(QString startDateTime, QString endDateTime)
    {
        m_series->removePoints(0, m_series->points().count());
        // Variable declaration and database initialization
        if (db.open())
        {
            QSqlQuery query(db);
            ...
            if (query.exec(queryString))
            {
                while (query.next())
                {
                    // Assignment of input to m_series
                    m_series->append(the input);
                }
            }
            db.close();
        }
    
        // re(?: paint, display, draw, ...)
    }
    

    view.h:

    class View : public QGraphicsView
    {
        Q_OBJECT
    
    public:
        View(QWidget *parent = Q_NULLPTR);
        ~View();
    
        void updateChart(QString startDateTime, QString endDateTime);
    
    private:
        Scene *m_scene;
        Chart *m_chart;
        QtCharts::QLineSeries *m_series;
        QtCharts::QDateTimeAxis *m_axisX;
        QtCharts::QValueAxis *m_axisY;
        QGraphicsSimpleTextItem *m_coordX;
        QGraphicsSimpleTextItem *m_coordY;
    };
    

    view.cpp:

    View::View(QWidget *parent) : QGraphicsView(parent)
    {
        m_scene = new Scene();
        m_chart = new Chart();
        m_series = new QtCharts::QLineSeries(m_chart);
        m_axisX = new QtCharts::QDateTimeAxis(m_chart);
        m_axisY = new QtCharts::QValueAxis(m_chart);
        m_coordX = new QGraphicsSimpleTextItem(m_chart);
        m_coordY = new QGraphicsSimpleTextItem(m_chart);
    
        m_chart->setGeometry(0, 0, 1400, 800);
        m_chart->addSeries(m_series);
        m_axisX->setFormat("d MMM yyyy");
        m_chart->addAxis(m_axisX, Qt::AlignBottom);
        m_series->attachAxis(m_axisX);
        m_axisY->setLabelFormat("%.6f");
        m_chart->addAxis(m_axisY, Qt::AlignLeft);
        m_series->attachAxis(m_axisY);
    
        m_scene->addItem(m_chart);
        setScene(m_scene);
    }
    

  • Qt Champions 2016

    Hi
    m_chart->update() will not do it ?



  • No, it would not.


  • Qt Champions 2016

    @vorlket
    ok?!
    And repaint() either ?



  • No, not with empty argument. It may work with QRect(F) argument referring to the graphics(item/scene/view), perhaps?


  • Qt Champions 2016

    @vorlket
    Nope the QRect is must likely a clipping / update area.

    Then Im not sure. I only tried QChart briefly and there it
    was enough to append the data and it would update.

    Wait some hours. Some of the others have used the Chart module far more than me. There
    must be something simple.



  • Remove then add item back works and this is what setChart method of QChartView seems to do. Not sure if this is efficient if there are many items and only a few of them change.


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