QML and C++ interaction

[cueMan]

Hi,

I'm trying to get an access to my c++ class from within QML. The idea is to run a function in C++ side when I press a rectangle area in QML. Also sending a signal from qml and catching it in c++ is an option. But all the examples I've found with google don't seem to work. I.e:

QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
view.rootContext()->setContextProperty("stopwatch", new Stopwatch);
view.show();

QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
view.rootContext()->setContextProperty("stopwatch", new Stopwatch);
view.show();

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import Qt 4.7
 
 Rectangle {
     width: 300
     height: 300
 
     MouseArea {
         anchors.fill: parent
         onClicked: {
             if (stopwatch.isRunning())
                 stopwatch.stop()
             else
                 stopwatch.start();
         }
     }
 }

import Qt 4.7

 Rectangle {
     width: 300
     height: 300

     MouseArea {
         anchors.fill: parent
         onClicked: {
             if (stopwatch.isRunning())
                 stopwatch.stop()
             else
                 stopwatch.start();
         }
     }
 }

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this would give me an error: TypeError: Result of expression 'stopwatch.start' [undefined] is not a function.

Also one example of connecting signal/slot:

QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
QObject *rootObject = dynamic_cast<QObject*>(view.rootObject());
QObject::connect(rootObject, SIGNAL(someqmlfunc()), &this, SLOT(somecpluplusfunc()));

QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
QObject *rootObject = dynamic_cast<QObject*>(view.rootObject());
QObject::connect(rootObject, SIGNAL(someqmlfunc()), &this, SLOT(somecpluplusfunc()));

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but conversion from QGraphicsObject to QObject is not possible.

Is there some working way to call a c++ function from within qml at the moment?

[cueMan]

Ah, forgot to mark the function I wish to run in C++ with Q_INVOKABLE. Now works.

[technoViking]

Hi,

I'm having the same issue, can you post how you got it working? the C++ function you just have to surround with Q_+INVOKABLE?

WHat if you want to send a SIGNAL from QML that has data the user entered (from QML). to a C++ slot that will process that data.

[cueMan]

Haven't yet needed a signal slot mechanism between QML and Qt but here's how you can call C++ code from QML:

First you need your class:

#include <QObject>
 
class MyClass : public QObject
{
    Q_OBJECT
public:
    explicit MyClass(QObject *parent = 0);
 
    Q_INVOKABLE void doThisAndThat(QString myString);
    Q_INVOKABLE QString getThisAndThat();
 
signals:
 
public slots:
 
private:
 
    QString localThisAndThat;
};

#include <QObject>

class MyClass : public QObject
{
    Q_OBJECT
public:
    explicit MyClass(QObject *parent = 0);

    Q_INVOKABLE void doThisAndThat(QString myString);
    Q_INVOKABLE QString getThisAndThat();
    
signals:

public slots:

private:

    QString localThisAndThat;
};

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And you can create the implementation as you wish, no need to use the Q_INVOKABLE on the implementation side, though.

The you need to introduce this class to QML like this:

QDeclarativeView::rootContext()->setContextProperty("qmlReferenceName", myClass);

QDeclarativeView::rootContext()->setContextProperty("qmlReferenceName", myClass);

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So you just give a string of your choice to qmlReferenceName, and pass your class on myClass. After this, you have this class as a global scope variable within your QML code:

Rectangle {
   MouseArea {
      anchors.fill: parent
      onClicked: { qmlReferenceName.doThisAndThat("It works!") }
   }
 
   Text {
      text: qmlReferenceName.getThisAndThat()
 
   }
}

Rectangle {
   MouseArea {
      anchors.fill: parent
      onClicked: { qmlReferenceName.doThisAndThat("It works!") }
   }
   
   Text {
      text: qmlReferenceName.getThisAndThat()

   }
}

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