QEventLoop Class Reference

\inmodule QtCore More...

#include <qeventloop.h>

Inheritance diagram for QEventLoop:

Collaboration diagram for QEventLoop:

Public Types
enum	ProcessEventsFlag {   AllEvents = 0x00 , ExcludeUserInputEvents = 0x01 , ExcludeSocketNotifiers = 0x02 , WaitForMoreEvents = 0x04 ,   X11ExcludeTimers = 0x08 , EventLoopExec = 0x20 , DialogExec = 0x40 , ApplicationExec = 0x80 }
	This enum controls the types of events processed by the processEvents() functions. More...

Public Slots
void	exit (int returnCode=0)
	Tells the event loop to exit with a return code.
void	quit ()
	Tells the event loop to exit normally.
Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Public Member Functions
	QEventLoop (QObject *parent=nullptr)
	Constructs an event loop object with the given parent.
	~QEventLoop ()
	Destroys the event loop object.
bool	processEvents (ProcessEventsFlags flags=AllEvents)
	Processes some pending events that match flags.
void	processEvents (ProcessEventsFlags flags, int maximumTime)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Process pending events that match flags for a maximum of maxTime milliseconds, or until there are no more events to process, whichever is shorter.
void	processEvents (ProcessEventsFlags flags, QDeadlineTimer deadline)
int	exec (ProcessEventsFlags flags=AllEvents)
	Enters the main event loop and waits until exit() is called.
bool	isRunning () const
	Returns true if the event loop is running; otherwise returns false.
void	wakeUp ()
	Wakes up the event loop.
bool	event (QEvent *event) override
	\reimp
Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)
	Constructs an object with parent object parent.
virtual	~QObject ()
	Destroys the object, deleting all its child objects.
virtual bool	eventFilter (QObject *watched, QEvent *event)
	Filters events if this object has been installed as an event filter for the watched object.
QString	objectName () const
Q_WEAK_OVERLOAD void	setObjectName (const QString &name)
	Sets the object's name to name.
void	setObjectName (QAnyStringView name)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
QBindable< QString >	bindableObjectName ()
bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false.
bool	isWindowType () const
	Returns true if the object is a window; otherwise returns false.
bool	isQuickItemType () const
	Returns true if the object is a QQuickItem; otherwise returns false.
bool	signalsBlocked () const noexcept
	Returns true if signals are blocked; otherwise returns false.
bool	blockSignals (bool b) noexcept
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it).
QThread *	thread () const
	Returns the thread in which the object lives.
bool	moveToThread (QThread *thread QT6_DECL_NEW_OVERLOAD_TAIL)
	Changes the thread affinity for this object and its children and returns true on success.
int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
	This is an overloaded function that will start a timer of type timerType and a timeout of interval milliseconds.
int	startTimer (std::chrono::nanoseconds time, Qt::TimerType timerType=Qt::CoarseTimer)
void	killTimer (int id)
	Kills the timer with timer identifier, id.
void	killTimer (Qt::TimerId id)
template<typename T >
T	findChild (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns the child of this object that can be cast into type T and that is called name, or \nullptr if there is no such object.
template<typename T >
QList< T >	findChildren (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects.
template<typename T >
T	findChild (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
const QObjectList &	children () const
	Returns a list of child objects.
void	setParent (QObject *parent)
	Makes the object a child of parent.
void	installEventFilter (QObject *filterObj)
	Installs an event filter filterObj on this object.
void	removeEventFilter (QObject *obj)
	Removes an event filter object obj from this object.
QMetaObject::Connection	connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
bool	disconnect (const char *signal=nullptr, const QObject *receiver=nullptr, const char *member=nullptr) const
bool	disconnect (const QObject *receiver, const char *member=nullptr) const
void	dumpObjectTree () const
	Dumps a tree of children to the debug output.
void	dumpObjectInfo () const
	Dumps information about signal connections, etc.
bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value.
bool	setProperty (const char *name, QVariant &&value)
QVariant	property (const char *name) const
	Returns the value of the object's name property.
QList< QByteArray >	dynamicPropertyNames () const
QBindingStorage *	bindingStorage ()
const QBindingStorage *	bindingStorage () const
QObject *	parent () const
	Returns a pointer to the parent object.
bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false.

Friends
class	QEventLoopLocker

Additional Inherited Members
Signals inherited from QObject
void	destroyed (QObject *=nullptr)
	This signal is emitted immediately before the object obj is destroyed, after any instances of QPointer have been notified, and cannot be blocked.
void	objectNameChanged (const QString &objectName, QPrivateSignal)
	This signal is emitted after the object's name has been changed.
Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
	\threadsafe
static QMetaObject::Connection	connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const typename QtPrivate::ContextTypeForFunctor< Func2 >::ContextType *context, Func2 &&slot, Qt::ConnectionType type=Qt::AutoConnection)
template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 &&slot)
static bool	disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
	\threadsafe
static bool	disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
static bool	disconnect (const QMetaObject::Connection &)
	Disconnect a connection.
template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object *receiver, Func2 slot)
template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, const QObject *receiver, void **zero)
Protected Member Functions inherited from QObject
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns \nullptr.
int	senderSignalIndex () const
int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal.
bool	isSignalConnected (const QMetaMethod &signal) const
virtual void	timerEvent (QTimerEvent *event)
	This event handler can be reimplemented in a subclass to receive timer events for the object.
virtual void	childEvent (QChildEvent *event)
	This event handler can be reimplemented in a subclass to receive child events.
virtual void	customEvent (QEvent *event)
	This event handler can be reimplemented in a subclass to receive custom events.
virtual void	connectNotify (const QMetaMethod &signal)
virtual void	disconnectNotify (const QMetaMethod &signal)
	QObject (QObjectPrivate &dd, QObject *parent=nullptr)
Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr
Properties inherited from QObject
QString	objectName
	the name of this object
Related Symbols inherited from QObject
template< class T > T	qobject_cast (const QObject *object)
	Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.
template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()
template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()
	QObjectList
	\macro Q_CLASSINFO(Name, Value)

Detailed Description

\inmodule QtCore

The QEventLoop class provides a means of entering and leaving an event loop.

At any time, you can create a QEventLoop object and call exec() on it to start a local event loop. From within the event loop, calling exit() will force exec() to return.

See also

QAbstractEventDispatcher

Definition at line 15 of file qeventloop.h.

Member Enumeration Documentation

ProcessEventsFlag

enum QEventLoop::ProcessEventsFlag

This enum controls the types of events processed by the processEvents() functions.

\value AllEvents All events. Note that \l{QEvent::DeferredDelete}{DeferredDelete} events are processed specially. See QObject::deleteLater() for more details.

\value ExcludeUserInputEvents Do not process user input events, such as ButtonPress and KeyPress. Note that the events are not discarded; they will be delivered the next time processEvents() is called without the ExcludeUserInputEvents flag.

\value ExcludeSocketNotifiers Do not process socket notifier events. Note that the events are not discarded; they will be delivered the next time processEvents() is called without the ExcludeSocketNotifiers flag.

\value WaitForMoreEvents Wait for events if no pending events are available.

\omitvalue X11ExcludeTimers \omitvalue EventLoopExec \omitvalue DialogExec \omitvalue ApplicationExec

See also

processEvents()

Enumerator
AllEvents
ExcludeUserInputEvents
ExcludeSocketNotifiers
WaitForMoreEvents
X11ExcludeTimers
EventLoopExec
DialogExec
ApplicationExec

Definition at line 25 of file qeventloop.h.

Constructor & Destructor Documentation

QEventLoop()

QEventLoop::QEventLoop ( QObject * parent = nullptr )

explicit

Constructs an event loop object with the given parent.

Definition at line 66 of file qeventloop.cpp.

~QEventLoop()

QEventLoop::~QEventLoop

(

)

Destroys the event loop object.

Definition at line 80 of file qeventloop.cpp.

Member Function Documentation

event()

bool QEventLoop::event ( QEvent * event )

overridevirtual

\reimp

Reimplemented from QObject.

Definition at line 304 of file qeventloop.cpp.

exec()

int QEventLoop::exec

(

ProcessEventsFlags

flags = AllEvents

)

Enters the main event loop and waits until exit() is called.

Returns the value that was passed to exit().

If flags are specified, only events of the types allowed by the flags will be processed.

It is necessary to call this function to start event handling. The main event loop receives events from the window system and dispatches these to the application widgets.

Generally speaking, no user interaction can take place before calling exec(). As a special case, modal widgets like QMessageBox can be used before calling exec(), because modal widgets use their own local event loop.

To make your application perform idle processing (i.e. executing a special function whenever there are no pending events), use a QChronoTimer with 0ns timeout. More sophisticated idle processing schemes can be achieved using processEvents().

See also

QCoreApplication::quit(), exit(), processEvents()

Definition at line 129 of file qeventloop.cpp.

exit

void QEventLoop::exit ( int returnCode = 0 )

slot

Tells the event loop to exit with a return code.

After this function has been called, the event loop returns from the call to exec(). The exec() function returns returnCode.

By convention, a returnCode of 0 means success, and any non-zero value indicates an error.

Note that unlike the C library function of the same name, this function does return to the caller – it is event processing that stops.

See also

QCoreApplication::quit(), quit(), exec()

Definition at line 261 of file qeventloop.cpp.

isRunning()

bool QEventLoop::isRunning

(

)

const

Returns true if the event loop is running; otherwise returns false.

The event loop is considered running from the time when exec() is called until exit() is called.

See also

exec(), exit()

Definition at line 280 of file qeventloop.cpp.

processEvents() [1/3]

void QEventLoop::processEvents	(	ProcessEventsFlags	flags,
		int	maxTime )

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Process pending events that match flags for a maximum of maxTime milliseconds, or until there are no more events to process, whichever is shorter.

Equivalent to calling:

processEvents(flags, QDeadlineTimer(maxTime));

Definition at line 212 of file qeventloop.cpp.

processEvents() [2/3]

void QEventLoop::processEvents	(	ProcessEventsFlags	flags,
		QDeadlineTimer	deadline )

Since

6.7

Process pending events that match flags until deadline has expired, or until there are no more events to process, whichever happens first. This function is especially useful if you have a long running operation and want to show its progress without allowing user input, i.e. by using the \l ExcludeUserInputEvents flag.

{Notes:} \list

• This function does not process events continuously; it returns after all available events are processed.
• Specifying the \l WaitForMoreEvents flag makes no sense and will be ignored. \endlist

Definition at line 234 of file qeventloop.cpp.

processEvents() [3/3]

bool QEventLoop::processEvents

(

ProcessEventsFlags

flags = AllEvents

)

Processes some pending events that match flags.

Returns true if pending events were handled; otherwise returns false.

This function is especially useful if you have a long running operation and want to show its progress without allowing user input; i.e. by using the \l ExcludeUserInputEvents flag.

This function is simply a wrapper for QAbstractEventDispatcher::processEvents(). See the documentation for that function for details.

Definition at line 97 of file qeventloop.cpp.

quit

void QEventLoop::quit ( )

slot

Tells the event loop to exit normally.

Same as exit(0).

See also

QCoreApplication::quit(), exit()

Definition at line 321 of file qeventloop.cpp.

wakeUp()

void QEventLoop::wakeUp

(

)

Wakes up the event loop.

See also

QAbstractEventDispatcher::wakeUp()

Definition at line 291 of file qeventloop.cpp.

Friends And Related Symbol Documentation

QEventLoopLocker

friend class QEventLoopLocker

friend

Definition at line 19 of file qeventloop.h.

---

The documentation for this class was generated from the following files:

• qtbase/src/corelib/kernel/qeventloop.h (26b8e99b1ce616a063fcbd0d67f44ba9e7712f23)
• qtbase/src/corelib/kernel/qeventloop.cpp (3af20bd8eb8c75017c5d6d138d7c42914ee5bee3)