Manipulating QML BarSeries graph values from C++

[jjgccg]

In QML, I have a HorizontalStackedBarSeries that looks like this:

        ChartView {
            title: ""
            width: ioSectionGraphWidth
            height: ioSectionGraphHeight
            legend.visible: true
            legend.font.pointSize: 15
            theme: ChartView.ChartThemeDark
            legend.alignment: Qt.AlignRight
            antialiasing: true

            HorizontalStackedBarSeries {
                id: ioBarchart
                objectName: "ioBarchart"
                axisY: BarCategoryAxis { categories: ["INPUT", "OUTPUT"] }
                BarSet { label: "G Power"; values: [2500, 0] }
                BarSet { label: "S Power"; values: [550, 0] }
                BarSet { label: "H Power"; values: [700, 0] }
                BarSet { label: "Total Output"; values: [0, 1500] }
            }
        }

Is it possible to add a new BarSet to the graph or manipulate an existing BarSet on the graph from C++? For example, could I change one of the values in BarSet { label: "S Power"; values: [550, 0] } to be BarSet { label: "S Power"; values: [123, 0] } from C++?

I know how to connect signals and slots and how to manipulate basic items like a Label from C++. For example, I was able to change a label in QML from 0 to 190 using C++ when a button is clicked in QML.

However, I haven't been able to find any resources of the manipulation of QML graphs from C++. How would I go about doing this?

Thank you in advance.

[J.Hilk]

hi @jjgccg

if you take a look at the BarSet documentation:

https://doc.qt.io/qt-5/qml-qtcharts-barset.html

you'll find, that BarSet has a couple of methods that should be useful:

remove, replace and append in your case.

You said, you know how to react to a signal from cpp.

Do that, and give your barsets and ID and you should be good to go :)

[jjgccg]

hey @j-hilk , Thank you for the information.

I've tried using the replace function in the documentation with QMetaObject::invokeMethod(). First, I gave each of the BarSet's an objectName as you can see here:

ChartView {
            title: ""
            width: ioSectionGraphWidth
            height: ioSectionGraphHeight
            legend.visible: true
            legend.font.pointSize: 15
            theme: ChartView.ChartThemeDark
            legend.alignment: Qt.AlignRight
            antialiasing: true

            HorizontalStackedBarSeries {
                id: ioBarchart
                objectName: "ioBarchart"
                axisY: BarCategoryAxis { categories: ["INPUT", "OUTPUT"] }
                BarSet { objectName: "gVal"; label: "G Power"; values: [0, 0] }
                BarSet { objectName: "sVal"; label: "S Power"; values: [550, 0] }
                BarSet { objectName: "hVal"; label: "H Power"; values: [700, 0] }
                BarSet { objectName: "totVal"; label: "Total Output"; values: [0, 1500] }
            }

Then I got a reference to the gVal BarSet:

gGraphValues = rootObject->findChild<QObject*>("gVal");

And then I tried invoking the method to change the value 0 to 2500:

    QMetaObject::invokeMethod(gGraphValues, "replace",
                              Q_ARG(int, 0),
                              Q_ARG(int, 2500));

Unfortunately this does not work. Do you know what is wrong?

[J.Hilk]

@jjgccg
I thought more along the line of, forwarding the signal to your QML component

//cpp signal
void updateGraph(int graphId, int index, int value);

//in qml

Connections{
     target: cppBackend
     onUpdateGraph:{
      if(graphId == 1) 
          graph1.replace(index, value)
      else if(....)
           ....
     }
}

[jjgccg]

@j-hilk I will try this out instead. I edited my reply above after trying the opposite, i.e. changing the value of the graph from C++ instead of changing it from QML after receiving a signal from C++.