Qt 5.9 | Qt Core | C++ Classes | QSignalBlocker

Qt 5.9.9 Reference Documentation

# QSignalBlocker Class

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

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

- List of all members, including inherited members

Note: All functions in this class are reentrant.

## Public Functions

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

## Detailed Description

Exception-safe wrapper around QObject::blockSignals()

QSignalBlocker can be used whereever 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(QObject *object)

Constructor. Calls object->blockSignals(true).

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

This is an overloaded function.

Calls object.blockSignals(true).

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

Move-constructs a signal blocker from other. other will have a no-op destructor, while repsonsibility for restoring the QObject::signalsBlocked() state is transferred to the new object.

### 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 QSignaBlocker'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.

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

Move-assigns this signal blocker from other. other will have a no-op destructor, while repsonsibility 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.