QQmlIncubationController Class

Detailed Description

In order to behave asynchronously and not introduce stutters or freezes in an application, the process of creating objects a QQmlIncubators must be driven only during the application's idle time. QQmlIncubationController allows the application to control exactly when, how often and for how long this processing occurs.

A QQmlIncubationController derived instance should be created and set on a QQmlEngine by calling the QQmlEngine::setIncubationController() method. Processing is then controlled by calling the QQmlIncubationController::incubateFor() or QQmlIncubationController::incubateWhile() methods as dictated by the application's requirements.

For example, this is an example of a incubation controller that will incubate for a maximum of 5 milliseconds out of every 16 milliseconds.

 class PeriodicIncubationController : public QObject,
                                      public QQmlIncubationController
 {
 public:
     PeriodicIncubationController() {
         startTimer(16);
     }

 protected:
     void timerEvent(QTimerEvent *) override {
         incubateFor(5);
     }
 };

Although the example works, it is heavily simplified. Real world incubation controllers try and maximize the amount of idle time they consume while not disturbing the application. Using a static amount of 5 milliseconds like above may both leave idle time on the table in some frames and disturb the application in others.

QQuickWindow, QQuickView, and QQuickWidget all pre-create an incubation controller that spaces out incubation over multiple frames using a more intelligent algorithm. You rarely have to write your own.