QEventLoop Class Reference

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

#include <qeventloop.h>

Inheritance diagram for QEventLoop:

Public Types
enum	ProcessEventsFlag {   AllEvents = 0x00, ExcludeUserInputEvents = 0x01, ExcludeSocketNotifiers = 0x02, WaitForMoreEvents = 0x04,   X11ExcludeTimers = 0x08, DeferredDeletion = 0x10, EventLoopExec = 0x20, DialogExec = 0x40 }
	This enum controls the types of events processed by the processEvents() functions. More...

Public Slots
void	quit ()
	Tells the event loop to exit normally. More...
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More...

Public Functions
int	exec (ProcessEventsFlags flags=AllEvents)
	Enters the main event loop and waits until exit() is called. More...
void	exit (int returnCode=0)
	Tells the event loop to exit with a return code. More...
bool	isRunning () const
	Returns true if the event loop is running; otherwise returns false. More...
bool	processEvents (ProcessEventsFlags flags=AllEvents)
	Processes pending events that match flags until there are no more events to process. More...
void	processEvents (ProcessEventsFlags flags, int maximumTime)
	Process pending events that match flags for a maximum of maxTime milliseconds, or until there are no more events to process, whichever is shorter. More...
	QEventLoop (QObject *parent=0)
	Constructs an event loop object with the given parent. More...
void	wakeUp ()
	Wakes up the event loop. More...
	~QEventLoop ()
	Destroys the event loop object. More...
Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More...
const QObjectList &	children () const
	Returns a list of child objects. More...
bool	connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
bool	disconnect (const char *signal=0, const QObject *receiver=0, const char *member=0)
bool	disconnect (const QObject *receiver, const char *member=0)
void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More...
void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More...
QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More...
virtual bool	event (QEvent *)
	This virtual function receives events to an object and should return true if the event e was recognized and processed. More...
virtual bool	eventFilter (QObject *, QEvent *)
	Filters events if this object has been installed as an event filter for the watched object. More...
template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More...
template<typename T >
QList< T >	findChildren (const QString &aName=QString()) 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. More...
template<typename T >
QList< T >	findChildren (const QRegExp &re) const
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. More...
void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More...
bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More...
void	killTimer (int id)
	Kills the timer with timer identifier, id. More...
virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More...
void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More...
QString	objectName () const
QObject *	parent () const
	Returns a pointer to the parent object. More...
QVariant	property (const char *name) const
	Returns the value of the object's name property. More...
Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More...
void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More...
void	setObjectName (const QString &name)
void	setParent (QObject *)
	Makes the object a child of parent. More...
bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value. More...
void	setUserData (uint id, QObjectUserData *data)
bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More...
int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More...
QThread *	thread () const
	Returns the thread in which the object lives. More...
QObjectUserData *	userData (uint id) const
virtual	~QObject ()
	Destroys the object, deleting all its child objects. More...

Additional Inherited Members
Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More...
Static Public Functions inherited from QObject
static bool	connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More...
static bool	connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
static bool	disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
	Disconnects signal in object sender from method in object receiver. More...
static bool	disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
static uint	registerUserData ()
static QString	tr (const char *sourceText, const char *comment=0, int n=-1)
static QString	trUtf8 (const char *sourceText, const char *comment=0, int n=-1)
Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More...
Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More...
virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More...
virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More...
virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More...
	QObject (QObjectPrivate &dd, QObject *parent=0)
int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More...
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 0. More...
int	senderSignalIndex () const
virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More...
Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr
Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject
Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()
T *	qobject_cast (QObject *object)
	QObjectList
void *	qt_find_obj_child (QObject *parent, const char *type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More...

Detailed Description

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 55 of file qeventloop.h.

Enumerations

ProcessEventsFlag

enum QEventLoop::ProcessEventsFlag

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

• AllEvents All events. Note that DeferredDelete events are processed specially. See QObject::deleteLater() for more details.

• 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.

• 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.

• WaitForMoreEvents Wait for events if no pending events are available.

• X11ExcludeTimers
• ExcludeUserInput
• WaitForMore
• EventLoopExec
• DialogExec
• DeferredDeletion deprecated - do not use.

See also

processEvents()

Enumerator
AllEvents
ExcludeUserInputEvents
ExcludeSocketNotifiers
WaitForMoreEvents
X11ExcludeTimers
DeferredDeletion
EventLoopExec
DialogExec

Definition at line 64 of file qeventloop.h.

                           {
        AllEvents = 0x00,
        ExcludeUserInputEvents = 0x01,
        ExcludeSocketNotifiers = 0x02,
        WaitForMoreEvents = 0x04,
#ifdef QT3_SUPPORT
        ExcludeUserInput = ExcludeUserInputEvents,
        WaitForMore = WaitForMoreEvents,
#endif
    X11ExcludeTimers = 0x08
#ifdef QT_DEPRECATED
    , DeferredDeletion = 0x10
#endif
        , EventLoopExec = 0x20
        , DialogExec = 0x40
    };

Constructors and Destructors

QEventLoop()

QEventLoop::QEventLoop ( QObject *  parent = 0 )

explicit

Constructs an event loop object with the given parent.

Definition at line 117 of file qeventloop.cpp.

    : QObject(*new QEventLoopPrivate, parent)
{
    Q_D(QEventLoop);
    if (!QCoreApplication::instance()) {
        qWarning("QEventLoop: Cannot be used without QApplication");
    } else if (!d->threadData->eventDispatcher) {
        QThreadPrivate::createEventDispatcher(d->threadData);
    }
}

~QEventLoop()

QEventLoop::~QEventLoop

(

)

Destroys the event loop object.

Definition at line 131 of file qeventloop.cpp.

{ }

Functions

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 QTimer with 0 timeout. More sophisticated idle processing schemes can be achieved using processEvents().

See also

QApplication::quit(), exit(), processEvents()

Definition at line 181 of file qeventloop.cpp.

Referenced by QTestEventLoop::enterLoop(), QScriptEngineDebuggerBackend::event(), QThread::exec(), QCoreApplication::exec(), QCoreApplication::hasPendingEvents(), QMenuPrivate::hideMenu(), QComboBox::hidePopup(), QMenuPrivate::hideUpToMenuBar(), QDBusConnectionPrivate::sendWithReply(), QHttpThreadDelegate::startRequestSynchronously(), and QNetworkSession::waitForOpened().

{
    Q_D(QEventLoop);
    //we need to protect from race condition with QThread::exit
    QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
    if (d->threadData->quitNow)
        return -1;

    if (d->inExec) {
        qWarning("QEventLoop::exec: instance %p has already called exec()", this);
        return -1;
    }
    d->inExec = true;
    d->exit = false;
    ++d->threadData->loopLevel;
    d->threadData->eventLoops.push(this);
    locker.unlock();

    // remove posted quit events when entering a new event loop
    QCoreApplication *app = QCoreApplication::instance();
    if (app && app->thread() == thread())
        QCoreApplication::removePostedEvents(app, QEvent::Quit);

#if defined(QT_NO_EXCEPTIONS)
    while (!d->exit)
        processEvents(flags | WaitForMoreEvents | EventLoopExec);
#else
    try {
        while (!d->exit)
            processEvents(flags | WaitForMoreEvents | EventLoopExec);
    } catch (...) {
        qWarning("Qt has caught an exception thrown from an event handler. Throwing\n"
                 "exceptions from an event handler is not supported in Qt. You must\n"
                 "reimplement QApplication::notify() and catch all exceptions there.\n");

        // copied from below
        locker.relock();
        QEventLoop *eventLoop = d->threadData->eventLoops.pop();
        Q_ASSERT_X(eventLoop == this, "QEventLoop::exec()", "internal error");
        Q_UNUSED(eventLoop); // --release warning
        d->inExec = false;
        --d->threadData->loopLevel;

        throw;
    }
#endif

    // copied above
    locker.relock();
    QEventLoop *eventLoop = d->threadData->eventLoops.pop();
    Q_ASSERT_X(eventLoop == this, "QEventLoop::exec()", "internal error");
    Q_UNUSED(eventLoop); // --release warning
    d->inExec = false;
    --d->threadData->loopLevel;

    return d->returnCode;
}

exit()

void QEventLoop::exit

(

int

returnCode = 0

)

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 288 of file qeventloop.cpp.

Referenced by QPatternist::NetworkLoop::error(), QThread::exit(), QCoreApplication::exit(), QTestEventLoop::exitLoop(), QPatternist::NetworkLoop::finished(), QCoreApplication::hasPendingEvents(), and quit().

{
    Q_D(QEventLoop);
    if (!d->threadData->eventDispatcher)
        return;

    d->returnCode = returnCode;
    d->exit = true;
    d->threadData->eventDispatcher->interrupt();
}

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 306 of file qeventloop.cpp.

Referenced by QScriptEngineDebuggerBackend::event(), QScriptEngineDebuggerBackend::resume(), and QScriptEngineDebuggerBackendPrivate::~QScriptEngineDebuggerBackendPrivate().

{
    Q_D(const QEventLoop);
    return !d->exit;
}

processEvents() [1/2]

bool QEventLoop::processEvents

(

ProcessEventsFlags

flags = AllEvents

)

Processes pending events that match flags until there are no more events to process.

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 ExcludeUserInputEvents flag.

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

Definition at line 148 of file qeventloop.cpp.

Referenced by exec(), and processEvents().

{
    Q_D(QEventLoop);
    if (!d->threadData->eventDispatcher)
        return false;
    if (flags & DeferredDeletion)
        QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
    return d->threadData->eventDispatcher->processEvents(flags);
}

processEvents() [2/2]

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

Process pending events that match flags for a maximum of maxTime milliseconds, or until there are no more events to process, whichever is shorter.

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 ExcludeUserInputEvents flag.

Notes:

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

Definition at line 255 of file qeventloop.cpp.

{
    Q_D(QEventLoop);
    if (!d->threadData->eventDispatcher)
        return;

    QElapsedTimer start;
    start.start();
    if (flags & DeferredDeletion)
        QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
    while (processEvents(flags & ~WaitForMoreEvents)) {
        if (start.elapsed() > maxTime)
            break;
        if (flags & DeferredDeletion)
            QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
    }
}

quit

void QEventLoop::quit ( )

slot

Tells the event loop to exit normally.

Same as exit(0).

See also

QCoreApplication::quit(), exit()

Definition at line 332 of file qeventloop.cpp.

Referenced by QScriptEngineDebuggerBackend::resume(), and QScriptEngineDebuggerBackendPrivate::~QScriptEngineDebuggerBackendPrivate().

{ exit(0); }

wakeUp()

void QEventLoop::wakeUp

(

)

Wakes up the event loop.

See also

QAbstractEventDispatcher::wakeUp()

Definition at line 317 of file qeventloop.cpp.

{
    Q_D(QEventLoop);
    if (!d->threadData->eventDispatcher)
        return;
    d->threadData->eventDispatcher->wakeUp();
}

---

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

• /src/corelib/kernel/qeventloop.h
• /src/corelib/kernel/qeventloop.cpp