qml chartview 发送到 C++ 时变为 nullptr

Question

I have a data source containing multiple series of data (not known upfront).

I want to add a LineSeries to a qml ChartView , so I tried to 'hook' the C++ side to the qml like so:

// data source
...
Q_PROPERTY(QtCharts::QChartView *chart READ chart WRITE setChart NOTIFY chartChanged)
public slots:
void setChart(QtCharts::QChartView *newChart) {
  qDebug() << "received new chart to draw on:" << newChart;
}

And in the qml, I send the chart to C++ more or less like:

...
ChartView { id: chart
  ...
}
Component.onCompleted: { backend.setChart(chart) }

Now the setChart is called allright, but the type does not appear to match: the incoming chart pointer is null:

> received new chart to draw on:  QWidget(0x0)

Relaxing the input type to plain QObject* has shown me that the actual type of the incoming object is QtQuick::DeclarativeChart .

How should I send the chart item to my C++ model? (Or should I use a totally different approach?)

Answer 1

If you need to update chart axis and series you should send them into c++ and update them i wrote an example you can take a look i think it dose what you want . On this example i converted c++ voice example from QWidget charts to QML chart but info in series are updating in c++ : QML chart updating in c++ Example

Answer 2

I ran into a similar problem (I needed access to the chart in C++ to hide some markers on the chart legend).

I was able to get access to the chart by passing a pointer to an existing series on the chart to my C++ code.

void GraphHelper::hideLegends(QtCharts::QScatterSeries *series) {
    QtCharts::QChart *chart = series->chart();
    // do something with the chart...
}

'''

Maybe this could help?