QQmlIncubationController instances drive the progress of QQmlIncubators. More...

#include <qqmlincubator.h>

Inheritance diagram for QQmlIncubationController:

Collaboration diagram for QQmlIncubationController:

Public Member Functions
	QQmlIncubationController ()
	Create a new incubation controller.

virtual	~QQmlIncubationController ()

QQmlEngine *	engine () const
	Return the QQmlEngine this incubation controller is set on, or 0 if it has not been set on any engine.

int	incubatingObjectCount () const
	Return the number of objects currently incubating.

void	incubateFor (int msecs)
	Incubate objects for msecs, or until there are no more objects to incubate.

void	incubateWhile (std::atomic< bool > *flag, int msecs=0)

Protected Member Functions
virtual void	incubatingObjectCountChanged (int)
	Called when the number of incubating objects changes.

Friends
class	QQmlEngine

class	QQmlEnginePrivate

class	QQmlIncubatorPrivate

Detailed Description

QQmlIncubationController instances drive the progress of QQmlIncubators.

\inmodule QtQml

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.

\l{QQuickWindow}, \l{QQuickView}, and \l{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.

Definition at line 68 of file qqmlincubator.h.

Constructor & Destructor Documentation

◆ QQmlIncubationController()

QQmlIncubationController::QQmlIncubationController ( )

Create a new incubation controller.

Definition at line 194 of file qqmlincubator.cpp.

◆ ~QQmlIncubationController()

QQmlIncubationController::~QQmlIncubationController ( )

virtual

Definition at line 200 of file qqmlincubator.cpp.

References QQmlEnginePrivate::get().

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Member Function Documentation

◆ engine()

QQmlEngine * QQmlIncubationController::engine ( ) const

Return the QQmlEngine this incubation controller is set on, or 0 if it has not been set on any engine.

Definition at line 210 of file qqmlincubator.cpp.

References QQmlEnginePrivate::get().

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◆ incubateFor()

void QQmlIncubationController::incubateFor ( int msecs )

Incubate objects for msecs, or until there are no more objects to incubate.

Definition at line 419 of file qqmlincubator.cpp.

References deadline, i, QQmlEnginePrivate::incubatorCount, and QQmlEnginePrivate::incubatorList.

Referenced by QQuickWindowIncubationController::incubate().

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◆ incubateWhile()

void QQmlIncubationController::incubateWhile	(	std::atomic< bool > *	flag,
		int	msecs = 0 )

Since: 5.15

Incubate objects while the atomic bool pointed to by flag is true, or until there are no more objects to incubate, or up to msecs if msecs is not zero.

Generally this method is used in conjunction with a thread or a UNIX signal that sets the bool pointed to by flag to false when it wants incubation to be interrupted.