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.

Update: Forum Guidelines & Code of Conduct

Solved How to free RAM after using QChartView?