Problem with data visualization in QCharts and multithreading

Davide87

Hello everyone.
I got a problem regarding QChartView and widgets in general when used with multithreading.

I got a code like this

QChart         *chart_plot;
QChartView     *chartView_plot;
QLineSeries    *series_plot;

in my mainwindow.h and like this

series_plot = new QLineSeries();
chart_plot = new QChart();
chart_plot->addSeries(series_plot);

// etc...

chartView_plot = new QChartView;
chartView_plot->setChart(chart_plot);
chartView_plot->setRenderHint(QPainter::Antialiasing,true);

ui->gridLayout_plots->addWidget(chartView_plot,1,0,1,3);

in my mainwindow.cpp ant it works fine with the following result:

However, since there are more charts in my GUI and everything starts beeing slower and less reactive, I was thinking about letting another thread to manage the data visualization.
Then i created another object "MyThread_navigation" with

QChart         *chart_plot;
QChartView     *chartView_plot;
QLineSeries    *series_plot;

in mythread_navigation.h and

void MyThread_navigation::setup_thread(QThread &cThread, QChartView *chartview)
{
series_plot = new QLineSeries();
chart_plot = new QChart();
chart_plot->addSeries(series_plot);

// etc...

chartView_plot = new QChartView(chartview);
chartView_plot->setChart(chart_plot);
chartView_plot->setRenderHint(QPainter::Antialiasing,true);

connect(&cThread,SIGNAL(started()),this,SLOT(start_thread()));
}

in mythread_navigation.cpp.
Then, I wrote

MyThread_navigation *worker_navigation;           // Worker for navigation data visualization
QThread             *thread_navigation;           // Thread for navigation data visualization

in mainwindow.h and this

chartView_plot = new QChartView();
chartView_plot->setRenderHint(QPainter::Antialiasing,true);

ui->gridLayout_plots->addWidget(chartView_plot,1,0,1,3);

thread_navigation = new QThread();
worker_navigation = new MyThread_navigation();

worker_navigation->setup_thread(*thread_navigation,chartView_plot);
worker_navigation->moveToThread(thread_navigation);

connect(this, SIGNAL(quit_threads()), thread_navigation, SLOT(quit()));
connect(this, SIGNAL(quit_threads()), worker_navigation, SLOT(deleteLater()));
connect(thread_navigation, SIGNAL(finished()), thread_navigation, SLOT(deleteLater()));

thread_navigation->start();

in mainwindow.cpp.

The result is the following:

Moreover, when I resize the GUI window, that small chart does not appear to change its size.
It seems that when I pass a widget to another class and move that class to my QThread object, my chart won't resize to the layout's size in which it is contained.

In previous codes I wrote something like

graph_surface = new Q3DSurface();
container     = QWidget::createWindowContainer(graph_surface);

ui->gridLayout_visual->addWidget(container,1,0,6,1);
graph_surface->setHorizontalAspectRatio(container->width()/container->height());
graph_surface->setHeight(container->height());

container->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
container->setFocusPolicy(Qt::StrongFocus);

// etc.

thread_visual = new QThread;
worker_visual = new MyThread_visualization();

worker_visual->setup_thread(*thread_visual, graph_surface);
worker_visual->moveToThread(thread_visual_RA);
thread_visual->start();

and It used to work fine. The problem is that createWindowContainer doesn't take a QChartView as a input (only QWindow apparently).
How can I solve this?
How can I "put" a QChartView (QWidget) in a container (if it solves my problem)?
Is there a better way to make another thread to manage data visualization on a chart?

Thank you in advance of any reply :-)
Bye bye

Christian Ehrlicher

You must not modify any gui elements outside the main gui thread. You can move the calculation into a separate thread and then send the result via signals and slots to the main gui thread.

Davide87

Thank you for your advice. I did as you said and it seems it's working well.