QEventLoop Class

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

Header	`#include <QEventLoop>`
CMake	`target_link_libraries(app PRIVATE Nt::Core)`
Module	Nt Core C++ Classes
Inherits	QObject

List of all members, including inherited members

Public Types

enum	ProcessEventsFlag
typedef	ProcessEventsFlags

Public Functions

	QEventLoop(QObject *parent = nullptr)
	~QEventLoop()
bool	processEvents(ProcessEventsFlags flags = AllEvents)
void	processEvents(ProcessEventsFlags flags, int maxTime)
void	processEvents(ProcessEventsFlags flags, QDeadlineTimer deadline)
int	exec(ProcessEventsFlags flags = AllEvents)
void	exit(int returnCode = 0)
bool	isRunning() const
void	wakeUp()

Public Slots

void

quit()

Detailed Description

An event loop dispatches timers, posted events and socket notifiers. Call exec() to run it until quit() or exit() is called, for example from a slot:

QEventLoop loop;
QTimer::singleShot(1000, [&loop] { loop.quit(); });
loop.exec();

See also QCoreApplication, QTimer and QSocketNotifier.

Differences from Qt

ExcludeUserInputEvents and ExcludeSocketNotifiers are accepted but ignored. A loop always runs the event dispatcher of the thread that calls exec() or processEvents(), and that dispatcher cannot be replaced.

Member Type Documentation

enum QEventLoop::ProcessEventsFlag

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

Constant	Description
`QEventLoop::AllEvents`	All pending events are processed.
`QEventLoop::ExcludeUserInputEvents`	Accepted for compatibility; it has no effect because Nt has no user input events.
`QEventLoop::ExcludeSocketNotifiers`	Accepted for compatibility; it has no effect, socket notifiers are always processed.
`QEventLoop::WaitForMoreEvents`	Block until an event is available instead of returning immediately.

typedef QEventLoop::ProcessEventsFlags

The ProcessEventsFlags type is a typedef for QFlags<ProcessEventsFlag>. It stores an OR combination of ProcessEventsFlag values.

Member Function Documentation

[explicit] QEventLoop::QEventLoop(QObject **parent* = nullptr)

Constructs an event loop with the given parent.

[override] QEventLoop::~QEventLoop()

Destroys the event loop.

int QEventLoop::exec(ProcessEventsFlags flags = AllEvents)

Enters the event loop and runs it until exit() or quit() is called, then returns the code passed to exit(). flags is accepted for compatibility and ignored. Returns -1 immediately if the loop is already running.

See also exit(), quit() and isRunning().

void QEventLoop::exit(int returnCode = 0)

Tells the event loop to exit with the return code returnCode, which exec() then returns. It is safe to call from any thread.

See also quit() and exec().

bool QEventLoop::isRunning() const

Returns true if the event loop is running in exec(); otherwise returns false.

See also exec() and exit().

bool QEventLoop::processEvents(ProcessEventsFlags flags = AllEvents)

Processes pending events once, according to flags, and returns true if any event, timer or notifier was handled. With WaitForMoreEvents it blocks until something is ready.

See also exec().

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

This is an overloaded function.

Processes the pending events for at most maxTime milliseconds, or until there are none left, as flags selects. It does not wait for new events, even with WaitForMoreEvents. Call it during a long computation to keep the program responsive.