QState Class

The QState class provides a general-purpose state for QStateMachine. More...

Header: #include <QState>
qmake: QT += core
Since: Qt 4.6
Inherits: QAbstractState.
Inherited By:


Public Types

enum ChildMode { ExclusiveStates, ParallelStates }
enum RestorePolicy { DontRestoreProperties, RestoreProperties }


Public Functions

QState(QState * parent = 0)
QState(ChildMode childMode, QState * parent = 0)
void addTransition(QAbstractTransition * transition)
QSignalTransition * addTransition(const QObject * sender, const char * signal, QAbstractState * target)
QAbstractTransition * addTransition(QAbstractState * target)
void assignProperty(QObject * object, const char * name, const QVariant & value)
ChildMode childMode() const
QAbstractState * errorState() const
QAbstractState * initialState() const
void removeTransition(QAbstractTransition * transition)
void setChildMode(ChildMode mode)
void setErrorState(QAbstractState * state)
void setInitialState(QAbstractState * state)
QList<QAbstractTransition *> transitions() const


void finished()
void propertiesAssigned()

Reimplemented Protected Functions

virtual bool event(QEvent * e)
virtual void onEntry(QEvent * event)
virtual void onExit(QEvent * event)

Additional Inherited Members

  • 1 public slot inherited from QObject
  • 11 static public members inherited from QObject
  • 3 protected functions inherited from QAbstractState
  • 9 protected functions inherited from QObject

Detailed Description

The QState class provides a general-purpose state for QStateMachine.

QState objects can have child states, and can have transitions to other states. QState is part of The State Machine Framework.

The addTransition() function adds a transition. The removeTransition() function removes a transition. The transitions() function returns the state's outgoing transitions.

The assignProperty() function is used for defining property assignments that should be performed when a state is entered.

Top-level states must be passed a QStateMachine object as their parent state, or added to a state machine using QStateMachine::addState().

States with Child States

The childMode property determines how child states are treated. For non-parallel state groups, the setInitialState() function must be called to set the initial state. The child states are mutually exclusive states, and the state machine needs to know which child state to enter when the parent state is the target of a transition.

The state emits the QState::finished() signal when a final child state (QFinalState) is entered.

The setErrorState() sets the state's error state. The error state is the state that the state machine will transition to if an error is detected when attempting to enter the state (e.g. because no initial state has been set).

Member Type Documentation

enum QState::ChildMode

This enum specifies how a state's child states are treated.

QState::ExclusiveStates0The child states are mutually exclusive and an initial state must be set by calling QState::setInitialState().
QState::ParallelStates1The child states are parallel. When the parent state is entered, all its child states are entered in parallel.

enum QState::RestorePolicy

This enum specifies the restore policy type. The restore policy takes effect when the machine enters a state which sets one or more properties. If the restore policy is set to RestoreProperties, the state machine will save the original value of the property before the new value is set.

Later, when the machine either enters a state which does not set a value for the given property, the property will automatically be restored to its initial value.

Only one initial value will be saved for any given property. If a value for a property has already been saved by the state machine, it will not be overwritten until the property has been successfully restored.

QState::DontRestoreProperties0The state machine should not save the initial values of properties and restore them later.
QState::RestoreProperties1The state machine should save the initial values of properties and restore them later.

See also QStateMachine::globalRestorePolicy and QState::assignProperty().

Property Documentation

childMode : ChildMode

This property holds the child mode of this state.

The default value of this property is QState::ExclusiveStates.

Access functions:

ChildMode childMode() const
void setChildMode(ChildMode mode)

errorState : QAbstractState *

This property holds the error state of this state.

Access functions:

QAbstractState * errorState() const
void setErrorState(QAbstractState * state)

initialState : QAbstractState *

This property holds the initial state of this state (one of its child states).

Access functions:

QAbstractState * initialState() const
void setInitialState(QAbstractState * state)

Member Function Documentation

QState::QState(QState * parent = 0)

Constructs a new state with the given parent state.

QState::QState(ChildMode childMode, QState * parent = 0)

Constructs a new state with the given childMode and the given parent state.


Destroys this state.

void QState::addTransition(QAbstractTransition * transition)

Adds the given transition. The transition has this state as the source. This state takes ownership of the transition.

QSignalTransition * QState::addTransition(const QObject * sender, const char * signal, QAbstractState * target)

Adds a transition associated with the given signal of the given sender object, and returns the new QSignalTransition object. The transition has this state as the source, and the given target as the target state.

QAbstractTransition * QState::addTransition(QAbstractState * target)

Adds an unconditional transition from this state to the given target state, and returns then new transition object.

void QState::assignProperty(QObject * object, const char * name, const QVariant & value)

Instructs this state to set the property with the given name of the given object to the given value when the state is entered.

See also propertiesAssigned().

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

Reimplemented from QObject::event().

void QState::finished() [signal]

This signal is emitted when a final child state of this state is entered.

See also QFinalState.

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

Reimplemented from QAbstractState::onEntry().

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

Reimplemented from QAbstractState::onExit().

void QState::propertiesAssigned() [signal]

This signal is emitted when all properties have been assigned their final value. If the state assigns a value to one or more properties for which an animation exists (either set on the transition or as a default animation on the state machine), then the signal will not be emitted until all such animations have finished playing.

If there are no relevant animations, or no property assignments defined for the state, then the signal will be emitted immediately before the state is entered.

See also QState::assignProperty() and QAbstractTransition::addAnimation().

void QState::removeTransition(QAbstractTransition * transition)

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

See also addTransition().

QList<QAbstractTransition *> QState::transitions() const

Returns this state's outgoing transitions (i.e. transitions where this state is the source state), or an empty list if this state has no outgoing transitions.

This function was introduced in Qt 4.7.

See also addTransition().

Notes provided by the Qt Community

No notes