Connecting Qt functionality with Qml

Sushma_MP

Hi ,

Am writing play function to play music in Qt Cpp file but my UI is in Qml if i wanted to move that music slider according to my current playing song how can i link qt functionality with that slider image on my UI

Jagh

So my first basic solution is this:
in C++:

// Update playtime information for UI
// repeat this every tick
engine->rootContext()->setContextProperty("playTime", secondsPlayed);

// set songLength property when you change a song
engine->rootContext()->setContextProperty("songLength", secondsSongLength);

in QML you have then say a value property for your slider:

Slider {
   value: playTime/songLength
}

QML binding will ensure that value will be recalculated each time the properties playTime/songLength are changed

raven-worx

@Sushma_MP
instead of consecutively writing context properties i would suggest a cleaner way. (i am not quite sure if property binding is really working for context properties?)

Create a custom (QObject derived) controller class and correctly define your properties. On each update notification just set the property.

//cpp
class MyController : public QObject
{
       Q_OBJECT
       Q_PROPERTY( qreal progress READ progress WRITE setProgress NOTIFY progressChanged )

...

signals:
     void progressChanged( qreal progress );

protected:
       qreal progress() const { return mProgress; }
       void setProgress(qreal progress)
       {
              if( mProgress != progress )
              {
                  mProgress = progress;
                  emit progressChanged(progress);
              }
       }

      qreal mProgress;
};

// register type to QML
qmlRegisterType<MyController>();  //tell QML the available properties, methods, etc.; Also this type wont be createable within QML
engine->rootContext()->setContextProperty( "MyControllerContextProperty", new MyController(engine) );

//qml
MyItem {
      id: root

      Connections {
              target: MyControllerContextProperty
              onProgress: root.doSomething()
      }

      // or also possible
      ProgressBar {
             value: MyControllerContextProperty.progress   //gets automatically updated when you update the property in C++
      }
}

This technique works with every QObject derived class. Read on here.