QSignalBlocker Class Reference

Exception-safe wrapper around QObject::blockSignals(). More...

#include <qobject.h>

Collaboration diagram for QSignalBlocker:

Public Member Functions
Q_NODISCARD_CTOR	QSignalBlocker (QObject *o) noexcept
	Constructor.
Q_NODISCARD_CTOR	QSignalBlocker (QObject &o) noexcept
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Calls {object}.blockSignals(true).
	~QSignalBlocker ()
	Destructor.
Q_NODISCARD_CTOR	QSignalBlocker (QSignalBlocker &&other) noexcept
	Move-constructs a signal blocker from other.
QSignalBlocker &	operator= (QSignalBlocker &&other) noexcept
	Move-assigns this signal blocker from other.
void	reblock () noexcept
	Re-blocks signals after a previous unblock().
void	unblock () noexcept
	Temporarily restores the QObject::signalsBlocked() state to what it was before this QSignalBlocker's constructor ran.

Detailed Description

Exception-safe wrapper around QObject::blockSignals().

Since

5.3

\inmodule QtCore

\reentrant

QSignalBlocker can be used wherever you would otherwise use a pair of calls to blockSignals(). It blocks signals in its constructor and in the destructor it resets the state to what it was before the constructor ran.

{
const QSignalBlocker blocker(someQObject);
// no signals here
}

is thus equivalent to

const bool wasBlocked = someQObject->blockSignals(true);
// no signals here
someQObject->blockSignals(wasBlocked);

except the code using QSignalBlocker is safe in the face of exceptions.

See also

QMutexLocker, QEventLoopLocker

Definition at line 442 of file qobject.h.

Constructor & Destructor Documentation

QSignalBlocker() [1/3]

QSignalBlocker::QSignalBlocker ( QObject *  object )

inlineexplicitnoexcept

Constructor.

Calls {object}->blockSignals(true).

Definition at line 465 of file qobject.h.

QSignalBlocker() [2/3]

QSignalBlocker::QSignalBlocker ( QObject &  o )

inlineexplicitnoexcept

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Calls {object}.blockSignals(true).

Definition at line 471 of file qobject.h.

~QSignalBlocker()

QSignalBlocker::~QSignalBlocker ( )

inline

Destructor.

Restores the QObject::signalsBlocked() state to what it was before the constructor ran, unless unblock() has been called without a following reblock(), in which case it does nothing.

Definition at line 501 of file qobject.h.

References QObject::blockSignals().

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QSignalBlocker() [3/3]

QSignalBlocker::QSignalBlocker ( QSignalBlocker &&  other )

inlinenoexcept

Move-constructs a signal blocker from other.

other will have a no-op destructor, while responsibility for restoring the QObject::signalsBlocked() state is transferred to the new object.

Definition at line 477 of file qobject.h.

References other().

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Member Function Documentation

operator=()

QSignalBlocker & QSignalBlocker::operator= ( QSignalBlocker &&  other )

inlinenoexcept

Move-assigns this signal blocker from other.

other will have a no-op destructor, while responsibility for restoring the QObject::signalsBlocked() state is transferred to this object.

The object's signals this signal blocker was blocking prior to being moved to, if any, are unblocked except in the case where both instances block the same object's signals and *this is unblocked while other is not, at the time of the move.

Definition at line 485 of file qobject.h.

References other().

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reblock()

void QSignalBlocker::reblock ( )

inlinenoexcept

Re-blocks signals after a previous unblock().

The numbers of reblock() and unblock() calls are not counted, so every reblock() undoes any number of unblock() calls.

Definition at line 507 of file qobject.h.

References QObject::blockSignals().

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unblock()

void QSignalBlocker::unblock ( )

inlinenoexcept

Temporarily restores the QObject::signalsBlocked() state to what it was before this QSignalBlocker's constructor ran.

To undo, use reblock().

The numbers of reblock() and unblock() calls are not counted, so every unblock() undoes any number of reblock() calls.

Definition at line 514 of file qobject.h.

References QObject::blockSignals().

Referenced by QMenuPrivate::hideMenu().

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

• qtbase/src/corelib/kernel/qobject.h
• qtbase/src/corelib/kernel/qobject.cpp