How to free RAM after using QChartView?

[HTWAMD]

Hey,

I'm using a simple code to draw a chart, here an example - just the values of the QLineSeries are faked:

QLineSeries *series = new QLineSeries();

series->append(0, 1);
series->append(1, 2);
series->append(2, 5);
series->append(3, 3);

QChart *chart = new QChart();
chart->legend()->hide();
chart->addSeries(series);
chart->createDefaultAxes();

QChartView *chartView = new QChartView(chart);
chartView->setRenderHint(QPainter::Antialiasing);
chartView->resize(800, 600);
chartView->show();

I now have the problem that I use more RAM with every call. What's the correct way to handle it?
I tried to save the pointer of the Chart, ChartView and LineSeries and constantly checking if the window is still open/active. If the window is closed, I tried to use the deleteLater function but this crashs my application.

Can someone help please? Thanks

[Christian Ehrlicher]

@HTWAMD said in How to free RAM after using QChartView?:

What's the correct way to handle it?

You're creating objects without deleting them - so delete them and the memory will be freed - C++ basics.

[HTWAMD]

Well yes, sure. But like I said using the delete or deleteLater function isn't working. It crashes the whole application.

chartView->deleteLater();
chart->deleteLater();
//Or
delete chartView;
delete chart; 

I tried these function after the window of the chart is closed but no success.

[Christian Ehrlicher]

@HTWAMD said in How to free RAM after using QChartView?:

It crashes the whole application.

Because you delete it twice:

https://doc.qt.io/qt-5/qchartview.html#QChartView-1 : The ownership of the chart is passed to the chart view.

And please provide a minimal example where it crashes - you code above doesn't show where/how you delete the objects.

[HTWAMD]

I tried some more stuff but I' cant deal with the Chart stuff :(

Here is - basically - my code I use (header + source, the ui contains just a widget and two spinboxes):

namespace Ui {
class EventDrawer;
}

class EventDrawer : public QWidget
{
    Q_OBJECT

public:
    explicit EventDrawer(QWidget *parent, QTableWidget* listEvents);
    ~EventDrawer();
    void draw_chart();

public slots:
    void closeEvent (QCloseEvent *event);

private slots:
    void on_spinBox_min_valueChanged(int arg1);
    void on_spinBox_max_valueChanged(int arg1);

private:
    Ui::EventDrawer *ui;

    QChart* Chart;
    QChartView* chartView;
    QVBoxLayout* LayoutChart;
    QLineSeries* series;
    QTableWidget* table_ptr;

    bool init;
    int min_value;
    int max_value;
};

#endif // EVENTDRAWER_H




#include "eventdrawer.h"
#include "ui_eventdrawer.h"

EventDrawer::EventDrawer(QWidget *parent, QTableWidget* listEvents) :
    ui(new Ui::EventDrawer)
{
    ui->setupUi(this);
    this->setStyleSheet(parent->styleSheet());

    init = true;
    min_value = 0;
    max_value = 0;

    table_ptr = listEvents;
    draw_chart();
    init = false;
}

EventDrawer::~EventDrawer()
{
    delete ui;
}

void EventDrawer::closeEvent (QCloseEvent *event)
{
    delete ui->widget->layout();

    event->accept();
}

void EventDrawer::draw_chart()
{
    int counter = 1;
    QMap<QString, int> InfoTypes;
    for (int i=0; i < table_ptr->rowCount(); i++)
    {
        int value = i;
        QString info_type = table_ptr->item(value, 1)->text();
        if (InfoTypes[info_type] == 0)
            InfoTypes[info_type] = counter++;
    }

    int event_type_count = InfoTypes.count();
    if (event_type_count == 0)
        return;


    int min = 9999999;
    int max = -9999999;

    series = new QLineSeries[event_type_count];
    for (int i=0; i < table_ptr->rowCount(); i++)
    {
        int value = i;
        if (ui->checkBox_oldFirst->isChecked())
            value = (table_ptr->rowCount()-1) - i;

        QString info_type = table_ptr->item(value, 1)->text();
        float info_value = table_ptr->item(value, 2)->text().toFloat();

        if (info_value < min)
            min = info_value;
        if (info_value > max)
            max = info_value;

        if (ui->checkBox_dateAxis->isChecked())
        {
            QDateTime timestamp = QDateTime::fromString(table_ptr->item(value, 3)->text(), "yyyy-MM-dd hh:mm:ss.zzz");
            series[InfoTypes[info_type]-1].append(timestamp.toMSecsSinceEpoch(), info_value);
        }
        else
        {
            series[InfoTypes[info_type]-1].append(i, info_value);
        }
        series[InfoTypes[info_type]-1].setName(info_type);
    }

    Chart = new QChart();
    for (int i=0; i < event_type_count; i++)
        Chart->addSeries(&series[i]);

    if (ui->checkBox_dateAxis->isChecked())
    {
        QDateTimeAxis *axisX = new QDateTimeAxis;
        axisX->setTickCount(14);
        axisX->setFormat("MM.dd hh:mm:ss");
        axisX->setTitleText("Date");
        Chart->addAxis(axisX, Qt::AlignBottom);
        series->attachAxis(axisX);
        Chart->axisX()->setTitleText("Date");

        QValueAxis *axisY = new QValueAxis;
        axisY->setLabelFormat("%i");
        Chart->addAxis(axisY, Qt::AlignLeft);
        series->attachAxis(axisY);
    }
    else
    {
        Chart->createDefaultAxes();
        Chart->axisX()->setRange(0, table_ptr->rowCount());
    }

    if (min_value != 0 || max_value != 0)
    {
        Chart->axisY()->setRange(min_value, max_value);
    }
    else
    {
        ui->spinBox_max->setValue(max);
        ui->spinBox_min->setValue(min);
    }

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

    LayoutChart = new QVBoxLayout();
    LayoutChart->addWidget(chartView);
    ui->widget->setLayout(LayoutChart);
}

void EventDrawer::on_spinBox_min_valueChanged(int arg1)
{
    if (init)
        return;

    min_value = arg1;
    Chart->axisY()->setRange(min_value, max_value);
}

void EventDrawer::on_spinBox_max_valueChanged(int arg1)
{
    if (init)
        return;

    max_value = arg1;
    Chart->axisY()->setRange(min_value, max_value);
}

What I would like to do now, is to delete / free the ram when the window is closed. So if the closeEvent function is called, delete the chartView, Chart, Series.
Could someone please show me how to do this?

[Christian Ehrlicher]

Again: please provide a minimal, compilable example if you think there is a crash and / or a memleak. Delete your chartView in the dtor and the memory will be freed afaics.

[HTWAMD]

Okay I made a very short, compilable example, here is the download link:
https://filetransfer.io/data-package/wck4NloP

Compile, run the application, click draw chart, close the window, crash.
Can you or anyone please tell me how to modify the code / the dtor to avoid the crash?

[Christian Ehrlicher]

First in the dtor only 'delete ui' is needed - the rest is deleted due to parent child relationships.

Second please take a look at

QLineSeries *series = new QLineSeries[event_type_count];
...
Chart->addSeries(&series[i]);

since addSeries() is taking ownership, it's later also calling 'delete &series[i]' - this can't work.

Use a QVector<QLineSeries*>, no need to hold it as member (at least not in your testcase).

[HTWAMD]

Thanks a lot.
dtor is now delete ui only and the QLineSeries using a QVector, now it's working perfectly :)

[Christian Ehrlicher]

@HTWAMD Then please mark this topic as solved, thx.