QStateMachine Class

QPushButton button;

QStateMachine machine;
QState *s1 = new QState();
s1->assignProperty(&button, "text", "Click me");

QFinalState *s2 = new QFinalState();
s1->addTransition(&button, &QPushButton::clicked, s2);

machine.addState(s1);
machine.addState(s2);
machine.setInitialState(s1);
machine.start();

Member Function Documentation

QStateMachine::QStateMachine(QObject *parent = nullptr)

Constructs a new state machine with the given parent.

[signal, since 5.4] void QStateMachine::runningChanged(bool running)

This signal is emitted when the running property is changed with running as argument.

Note: Notifier signal for property running.

This function was introduced in Qt 5.4.

See also QStateMachine::running.

[slot] void QStateMachine::start()

Starts this state machine. The machine will reset its configuration and transition to the initial state. When a final top-level state (QFinalState) is entered, the machine will emit the finished() signal.

See also started(), finished(), stop(), initialState(), and setRunning().

[private signal] void QStateMachine::started()

This signal is emitted when the state machine has entered its initial state (QStateMachine::initialState).

Note: This is a private signal. It can be used in signal connections but cannot be emitted by the user.

See also QStateMachine::finished() and QStateMachine::start().

[slot] void QStateMachine::stop()

Stops this state machine. The state machine will stop processing events and then emit the stopped() signal.

See also stopped(), start(), and setRunning().

[private signal] void QStateMachine::stopped()

This signal is emitted when the state machine has stopped.

Note: This is a private signal. It can be used in signal connections but cannot be emitted by the user.

See also QStateMachine::stop() and QStateMachine::finished().

[virtual] QStateMachine::~QStateMachine()

Destroys this state machine.

void QStateMachine::addDefaultAnimation(QAbstractAnimation *animation)

Adds a default animation to be considered for any transition.

void QStateMachine::addState(QAbstractState *state)

Adds the given state to this state machine. The state becomes a top-level state and the state machine takes ownership of the state.

If the state is already in a different machine, it will first be removed from its old machine, and then added to this machine.

See also removeState() and setInitialState().

bool QStateMachine::cancelDelayedEvent(int id)

Cancels the delayed event identified by the given id. The id should be a value returned by a call to postDelayedEvent(). Returns true if the event was successfully cancelled, otherwise returns false.

Note: This function is thread-safe.

See also postDelayedEvent().

void QStateMachine::clearError()

Clears the error string and error code of the state machine.

QSet<QAbstractState *> QStateMachine::configuration() const

Returns the maximal consistent set of states (including parallel and final states) that this state machine is currently in. If a state s is in the configuration, it is always the case that the parent of s is also in c. Note, however, that the machine itself is not an explicit member of the configuration.

QList<QAbstractAnimation *> QStateMachine::defaultAnimations() const

Returns the list of default animations that will be considered for any transition.

QStateMachine::Error QStateMachine::error() const

Returns the error code of the last error that occurred in the state machine.

QString QStateMachine::errorString() const

Returns the error string of the last error that occurred in the state machine.

Note: Getter function for property errorString.

[override virtual protected] bool QStateMachine::event(QEvent *e)

Reimplements: QState::event(QEvent *e).

[override virtual] bool QStateMachine::eventFilter(QObject *watched, QEvent *event)

Reimplements: QObject::eventFilter(QObject *watched, QEvent *event).

QState::RestorePolicy QStateMachine::globalRestorePolicy() const

Returns the restore policy of the state machine.

Note: Getter function for property globalRestorePolicy.

See also setGlobalRestorePolicy().

bool QStateMachine::isAnimated() const

Returns whether animations are enabled for this state machine.

Note: Getter function for property animated.

[override virtual protected] void QStateMachine::onEntry(QEvent *event)

Reimplements: QState::onEntry(QEvent *event).

This function will call start() to start the state machine.

[override virtual protected] void QStateMachine::onExit(QEvent *event)

Reimplements: QState::onExit(QEvent *event).

This function will call stop() to stop the state machine and subsequently emit the stopped() signal.

int QStateMachine::postDelayedEvent(QEvent *event, int delay)

Posts the given event for processing by this state machine, with the given delay in milliseconds. Returns an identifier associated with the delayed event, or -1 if the event could not be posted.

This function returns immediately. When the delay has expired, the event will be added to the state machine's event queue for processing. The state machine takes ownership of the event and deletes it once it has been processed.

You can only post events when the state machine is running.

Note: This function is thread-safe.

See also cancelDelayedEvent() and postEvent().

[since 5.15] int QStateMachine::postDelayedEvent(QEvent *event, std::chrono::milliseconds delay)

This is an overloaded function.

Posts the given event for processing by this state machine, with the given delay in milliseconds. Returns an identifier associated with the delayed event, or -1 if the event could not be posted.

This function returns immediately. When the delay has expired, the event will be added to the state machine's event queue for processing. The state machine takes ownership of the event and deletes it once it has been processed.

You can only post events when the state machine is running.

Note: This function is thread-safe.

This function was introduced in Qt 5.15.

See also cancelDelayedEvent() and postEvent().

void QStateMachine::postEvent(QEvent *event, QStateMachine::EventPriority priority = NormalPriority)

Posts the given event of the given priority for processing by this state machine.

This function returns immediately. The event is added to the state machine's event queue. Events are processed in the order posted. The state machine takes ownership of the event and deletes it once it has been processed.

You can only post events when the state machine is running or when it is starting up.

Note: This function is thread-safe.

See also postDelayedEvent().

void QStateMachine::removeDefaultAnimation(QAbstractAnimation *animation)

Removes animation from the list of default animations.

void QStateMachine::removeState(QAbstractState *state)

Removes the given state from this state machine. The state machine releases ownership of the state.

See also addState().

void QStateMachine::setAnimated(bool enabled)

Sets whether animations are enabled for this state machine.

Note: Setter function for property animated.

See also isAnimated().

void QStateMachine::setGlobalRestorePolicy(QState::RestorePolicy restorePolicy)

Sets the restore policy of the state machine to restorePolicy. The default restore policy is QState::DontRestoreProperties.

Note: Setter function for property globalRestorePolicy.

See also globalRestorePolicy().