- Qt 5.15
- Qt Core
- C++ Classes
- QSignalBlocker
- Qt 5.15.18 Reference Documentation

# QSignalBlocker Class

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

Header: | #include <QSignalBlocker>
qmake: | QT += core
Since: | Qt 5.3

This class was introduced in Qt 5.3.

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Functions

| QSignalBlocker(QSignalBlocker &&other)
| QSignalBlocker(QObject &object)
| QSignalBlocker(QObject *object)
QSignalBlocker & | operator=(QSignalBlocker &&other)
| ~QSignalBlocker()
void | reblock()
void | unblock()

## Detailed Description

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 and QEventLoopLocker.

## Member Function Documentation

### QSignalBlocker::QSignalBlocker(QSignalBlocker &&other)

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.

### QSignalBlocker::QSignalBlocker(QObject &object)

This is an overloaded function.

Calls object.blockSignals(true).

### QSignalBlocker::QSignalBlocker(QObject *object)

Constructor. Calls object->blockSignals(true).

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

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.

### QSignalBlocker::~QSignalBlocker()

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.

### void QSignalBlocker::reblock()

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.

### void QSignalBlocker::unblock()

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.