C++ and QML

[AB_TrP]

Hi everyone,

I am having trouble with something that is probably so simple but I cant seem to figure it out...I have a MainWindow that is a QML object which has a child Item as a separate QML file. When I click a button on the main window, this child item becomes visible and some data is dynamically displayed inside a text item within it, which gets updated every second. The data is generated with a c++ class object that I have registered as a QML object and everything work fine...

The problem is, now I want to have access to the same data that appears in the child window and also display it in a text item on the main window....I assumed its simple and all i need to do is exactly the same i did for the child window, and that is to include the C++ registered object as a child item in the main window, but for some reason the data is not updating on the main window... any ideas why this might be happening?

I am very new to Qt so apologies for my ignorance :D
I hope what i wrote makes sense

[J.Hilk]

@AB_TrP

very hard to tell without any code 😉 can you show as the "MainWindow" file ?

an other instance of the cpp class can be a way but it may as well fail, depending on how you registered the class.

There are QML was to forward a property as well. Many ways to the desired outcome

code example will help tremendously

[AB_TrP]

@J-Hilk
Yes sure, here is the snippet of the code Im using in the MainWindow:

@MainWindow.qml

import IGPSData 1.1
    Text
    {
        id:txtData
        anchors.left: parent.left
        anchors.leftMargin: 5
        anchors.top: parent.top
        anchors.topMargin: 80
        text: cGPSData.getGPSData()
        visible: true
        font.family:  "Helvetica [Cronyx]"
        font.bold: true
        font.pixelSize: parent.width * 0.08
        color: "#ffffff"


    }
// this is the registered C++ class,
    CGPSData{
        id: cGPSData
    }


    Connections
    {
         target: cGPSData
         onSigGPSDataChanged:
         {
             txtData.text= cGPSData.getGPSData()
         }
    }

I have the exact same code in the child window and that works just fine

[AB_TrP]

@J-Hilk

as for forwarding a property, I came across the alias property but i think this only works when you want to forward a property from the parent to the children and not the other direction as I want...am I correct?

[KroMignon]

@AB_TrP Your QML code seems strange to me, can you show the header of CGPSData?

For me, it should be something like:

class CGPSData : public QObject
{
     Q_OBJECT

     Q_PROPERTY(QString gpsData  READ getGPSData NOTIFY gpsDataChanged)
public
   explicit CGPSData(QObject * parent = 0);

   QString getGPSData() const { return m_gpsData; }
   void setGpsData(const QString &gpsData)
   {
        if(gpsData != m_gpsData)
        {
            m_gpsData = gpsData;
            emit gpsDataChanged();
        }
   }
signals:
    void gpsDataChanged();

private:
    QString m_gpsData;
};

And then, in your QML

import IGPSData 1.1
// this is the registered C++ class,
    CGPSData{
        id: cGPSData
    }
    
    Text
    {
        id:txtData
        anchors.left: parent.left
        anchors.leftMargin: 5
        anchors.top: parent.top
        anchors.topMargin: 80
        text: cGPSData.gpsData
        visible: true
        font.family:  "Helvetica [Cronyx]"
        font.bold: true
        font.pixelSize: parent.width * 0.08
        color: "#ffffff"
    }