Chapter 2: Connecting to C++ Methods and Signals

Suppose we want PieChart to have a "clearChart()" method that erases the chart and then emits a "chartCleared" signal. Our app.qml would be able to call clearChart() and receive chartCleared() signals like this:


[Missing image extending-tutorial-chapter2.png]

To do this, we add a clearChart() method and a chartCleared() signal to our C++ class:

    ...
    ...
    ...

The use of Q_INVOKABLE makes the clearChart() method available to the Qt Meta-Object system, and in turn, to QML. Note that it could have been declared as as a Qt slot instead of using Q_INVOKABLE, as slots are also callable from QML. Both of these approaches are valid.

The clearChart() method simply changes the color to Qt::transparent, repaints the chart, then emits the chartCleared() signal:


Now when we run the application and click the window, the pie chart disappears, and the application outputs:

The chart has been cleared

Try out the example yourself with the updated code in Qt's examples/tutorials/extending/chapter2-methods directory.