QEventLoop

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

Inheritance diagram of PySide2.QtCore.QEventLoop

Synopsis

Functions

Slots

Detailed Description

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.

class PySide2.QtCore.QEventLoop([parent=None])
param parent

PySide2.QtCore.QObject

Constructs an event loop object with the given parent .

PySide2.QtCore.QEventLoop.ProcessEventsFlag

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

Constant

Description

QEventLoop.AllEvents

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

QEventLoop.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 flag.

QEventLoop.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 flag.

QEventLoop.WaitForMoreEvents

Wait for events if no pending events are available.

See also

processEvents()

PySide2.QtCore.QEventLoop.exec_([flags=QEventLoop.AllEvents])
Parameters

flagsProcessEventsFlags

Return type

int

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 . As a special case, modal widgets like QMessageBox can be used before calling , 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() .

PySide2.QtCore.QEventLoop.exit([returnCode=0])
Parameters

returnCode – int

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

quit() quit() exec()

PySide2.QtCore.QEventLoop.isRunning()
Return type

bool

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()

PySide2.QtCore.QEventLoop.processEvents([flags=QEventLoop.AllEvents])
Parameters

flagsProcessEventsFlags

Return type

bool

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 processEvents() . See the documentation for that function for details.

PySide2.QtCore.QEventLoop.processEvents(flags, maximumTime)
Parameters
  • flagsProcessEventsFlags

  • maximumTime – int

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.

PySide2.QtCore.QEventLoop.quit()

Tells the event loop to exit normally.

Same as exit(0).

See also

quit() exit()

PySide2.QtCore.QEventLoop.wakeUp()

Wakes up the event loop.

See also

wakeUp()