Connecting C++ with QML using Q_INVOKABLE

c++ qt qml qt-slot
user123_456 picture user123_456 · Feb 18, 2012 · Viewed 32k times · Source

I have a Qt function:

void MainWindow::button_clicked(Qstring a, Qstring b, Qstring c, Qstring d)

I collect data from QML and I want to pass data to this function which is in Qt. So I know I need to use Q_INVOKABLE but don't know really how to use it.

And one more thing is it possible to invoke some other function when invoke this certain above.
For example: I invoke the above function but in her body I invoke refresh() function. Is this possible?

Answer

Frank Osterfeld picture Frank Osterfeld · Feb 18, 2012

To be able to call a method from QML, you must either mark it with Q_INVOKABLE or as a slot. I prefer Q_INVOKABLE if it's not meant to be used as a slot, as its more minimal. 

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
...
    Q_INVOKABLE void buttonClicked( const QString& a, const QString& b, const QString& c, const QString& d );
....
};

void MainWindow::buttonClicked( const QString& a, const QString& b, const QString& c, const QString& d ) {
   ...do stuff
   update(); //example
}

The implementation of buttonClicked() can contain any C++ code.

To make the main window instance accessible from QML, you must register it, e.g.

QDeclarativeView* view = ...your view
view->rootContext()->setContextProperty( "_mainWindow", mainWindow );

Once registered, you can call buttonClicked from QML:

_mainWindow.buttonClicked("foo", "bar", "c", "d")

Related questions

'QML Connections: Cannot assign to non-existent Property' despite the opposite being true

So, I checked the following questions, which seemed most similar to my existing problem: QML: Using cpp signal in QML always results in "Cannot assign to non-existent property" Unfortunately that did not help. (Nor did any other solution that I …

Read More
C++ signal to QML slot in Qt

I want to send a Signal from C++ to a Slot in my QML File. I already got it working without and primitive type parameters, although if I want to send a QString to my QML Slot I get an …

Read More
How to access C++ enum from QML?

class StyleClass : public QObject { public: typedef enum { STYLE_RADIAL, STYLE_ENVELOPE, STYLE_FILLED } Style; Style m_style; //... }; The .h file has the above code. How to access the above enum through QML?

Read More