Refreshing a QML embedded within QQuickWidget in a QWidget application

[Alexiss]

Hey,

I have some 'analog' gauge to create and it appears that the best way to create them is using QtQuick. However I'm working within a qWidget environment, where the gauge's value is determined and sent to the view by a counter.

I managed to embedded my qml view in a QQuickWidget and to bind qml and qWidget, according to a connections qml object and some signals/slots. The QQuickWidget is in a layout.

I add a c++ function which is called every 100ms for cyclic, actions like the incrementation of a counter which has to simulate the gauge evolution.

During the runtime, all looks good (qml text refreshed by the c++ counter incrementation) but after some iterations, all is frozen in the qml. And I really don't know why. I tried to call some update() or repaint() functions or to reload the qml source, nothing happens...

Exists it a method to force it to refresh the printed data ?
Could you give me an hand please ?

piece of my code below,

Thank you

homePage.cpp

#include "cpagehome.h"
#include <QGridLayout>
#include <QtQuick>

#include "pagemanager.h"

CPageHome::CPageHome(PageManager * parent)
{
    // Save address of parent
    m_parent = parent;

    QQuickWidget * mp_view = new QQuickWidget;

    mp_data = new Data();

    //qmlRegisterType<Data>("DATA", 1, 0, "Data");
    mp_view->rootContext()->setContextProperty("file", mp_data);

    mp_data->setValue(100);
    
//    mp_data->set_i_value(10);
//    mp_view->rootContext()->setContextProperty("mpData",mp_data);

    mp_view->setAttribute(Qt::WA_AlwaysStackOnTop, true);
    mp_view->setAttribute(Qt::WA_TranslucentBackground, true);
    mp_view->setClearColor(Qt::transparent);
    mp_view->setResizeMode(QQuickWidget::SizeRootObjectToView);/* Le QML fit au qwidget */
    
    mp_view->setSource(QUrl("qrc:/testQML.qml"));

    // Add widget to the layout
    m_layout = new QGridLayout(this);
    m_layout->addWidget(mp_view);

}

void CPageHome::onActive(int activePage)
{
    /* called every 100 ms */
    static int hi_value = mp_data->getValue();

    mp_data->setValue(hi_value);

//    mp_view->engine()->clearComponentCache();
//    mp_view->setSource(QUrl(QStringLiteral("qrc:/testQML.qml")));


    /*
    if (hi_value % 2 == 0)
    {
        m_parent->showButtons(100);
    }
*/

    qDebug() << "mp_data: " << mp_data->getValue() ;
    //mp_view->rootContext()->setContextProperty("mpData",mp_data);
    //mp_view->setSource(QUrl(QStringLiteral("qrc:/testQML.qml")));
    //mp_view->repaint();
    //mp_view->update();

    //mp_view->resize(10*hi_value,10*hi_value);
    //m_layout->removeWidget(mp_view);

    //m_layout->addWidget(btn,1,2);
    //mp_view->adjustSize();
    //mp_view->updateGeometry();

    hi_value +=1;
}

CPageHome::~CPageHome()
{

}

datafile.cpp, used to transfer data between qml and qWidget

#include "data.h"

Data::Data()
{
    mi_value = 0;
}

Data::~Data()
{

}

int Data::getValue(void)
{
    return mi_value;
}

void Data::setValue(int oi_value)
{
    mi_value = oi_value;
    emit valueChanged(mi_value);
}

datafile.h

#ifndef DATA_H
#define DATA_H

#include <QObject>
#include <QWidget>

class Data : public QObject
{
    Q_OBJECT

    Q_PROPERTY(int value READ getValue WRITE setValue NOTIFY valueChanged)
public:
    Data();
    virtual ~Data();
    Q_INVOKABLE int getValue(void);
    Q_INVOKABLE void setValue(int oi_value);

signals:
    void valueChanged(int oi_value);

private:
    int mi_value;
};

#endif // DATA_H

testQML.qml

import QtQuick 2.4
import QtQuick.Controls 1.0

Item {
    width: 800
    height: 480

    Rectangle{
        id: rect
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter
        height: parent.height/3
        width: height
        color: 'coral'

        Text{
            id: textBox
            text: file.getValue()
            onTextChanged: {
                textBox.text = connection.newValue;
            }

            Connections{
                id: connection
                target: file
                property int newValue: 1000
                onValueChanged:
                {
                    console.log("oi_value : " + oi_value);
                    newValue = oi_value;
                    textBox.text = oi_value + '';
                }
            }
        }
    }
}

A QTimer in the pageManager is launched at the beginning, and generates signals to call onActive function.

[Alexiss]

Anyone has any idea ? :/ I'm really stuck

[J.Hilk]

hi @Alexiss and welcome

one thing jumps to my mind, you should actually check if the value differs - that's the standard way to do it, and you should check if the setValue function is still called and just the Ui doesn't display the change.

void Data::setValue(int oi_value)
{
   qDebug() << Q_FUNC_INFO << oi_value << "same value?" << (mi_value == oi_value);
    if(mi_value == oi_value)
       return;
    mi_value = oi_value;
    emit valueChanged(mi_value);
}

[Alexiss]

@J.Hilk Thanks for your test, I checked it and the setValue function is normally called with the right value and the display still doesn't display the change.