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QHistoryState Class

The QHistoryState class provides a means of returning to a previously active substate. More...

Header: #include <QHistoryState>
qmake: QT += core
Since: Qt 4.6
Inherits: QAbstractState

Public Types

enum HistoryType { ShallowHistory, DeepHistory }

Properties

Public Functions

QHistoryState(QState * parent = 0)
QHistoryState(HistoryType type, QState * parent = 0)
~QHistoryState()
QAbstractState * defaultState() const
HistoryType historyType() const
void setDefaultState(QAbstractState * state)
void setHistoryType(HistoryType type)

Signals

void defaultStateChanged()
void historyTypeChanged()

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 QHistoryState class provides a means of returning to a previously active substate.

A history state is a pseudo-state that represents the child state that the parent state was in the last time the parent state was exited. A transition with a history state as its target is in fact a transition to one of the other child states of the parent state. QHistoryState is part of The State Machine Framework.

Use the setDefaultState() function to set the state that should be entered if the parent state has never been entered. Example:

QStateMachine machine;

QState *s1 = new QState();
QState *s11 = new QState(s1);
QState *s12 = new QState(s1);

QHistoryState *s1h = new QHistoryState(s1);
s1h->setDefaultState(s11);

machine.addState(s1);

QState *s2 = new QState();
machine.addState(s2);

QPushButton *button = new QPushButton();
// Clicking the button will cause the state machine to enter the child state
// that s1 was in the last time s1 was exited, or the history state's default
// state if s1 has never been entered.
s1->addTransition(button, SIGNAL(clicked()), s1h);

By default a history state is shallow, meaning that it won't remember nested states. This can be configured through the historyType property.

Member Type Documentation

enum QHistoryState::HistoryType

This enum specifies the type of history that a QHistoryState records.

ConstantValueDescription
QHistoryState::ShallowHistory0Only the immediate child states of the parent state are recorded. In this case a transition with the history state as its target will end up in the immediate child state that the parent was in the last time it was exited. This is the default.
QHistoryState::DeepHistory1Nested states are recorded. In this case a transition with the history state as its target will end up in the most deeply nested descendant state the parent was in the last time it was exited.

Property Documentation

defaultState : QAbstractState *

This property holds the default state of this history state.

Access functions:

QAbstractState * defaultState() const
void setDefaultState(QAbstractState * state)

Notifier signal:

void defaultStateChanged()[see note below]

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

historyType : HistoryType

This property holds the type of history that this history state records.

The default value of this property is QHistoryState::ShallowHistory.

Access functions:

HistoryType historyType() const
void setHistoryType(HistoryType type)

Notifier signal:

void historyTypeChanged()[see note below]

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

Member Function Documentation

QHistoryState::QHistoryState(QState * parent = 0)

Constructs a new shallow history state with the given parent state.

QHistoryState::QHistoryState(HistoryType type, QState * parent = 0)

Constructs a new history state of the given type, with the given parent state.

QHistoryState::~QHistoryState()

Destroys this history state.

QAbstractState * QHistoryState::defaultState() const

Returns this history state's default state. The default state indicates the state to transition to if the parent state has never been entered before.

Note: Getter function for property defaultState.

See also setDefaultState().

[signal] void QHistoryState::defaultStateChanged()

This signal is emitted when the defaultState property is changed.

This function was introduced in Qt 5.4.

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

Note: Notifier signal for property defaultState.

See also QHistoryState::defaultState.

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

Reimplemented from QObject::event().

HistoryType QHistoryState::historyType() const

Returns the type of history that this history state records.

Note: Getter function for property historyType.

See also setHistoryType().

[signal] void QHistoryState::historyTypeChanged()

This signal is emitted when the historyType property is changed.

This function was introduced in Qt 5.4.

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

Note: Notifier signal for property historyType.

See also QHistoryState::historyType.

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

Reimplemented from QAbstractState::onEntry().

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

Reimplemented from QAbstractState::onExit().

void QHistoryState::setDefaultState(QAbstractState * state)

Sets this history state's default state to be the given state. state must be a sibling of this history state.

Note that this function does not set state as the initial state of its parent.

Note: Setter function for property defaultState.

See also defaultState().

void QHistoryState::setHistoryType(HistoryType type)

Sets the type of history that this history state records.

Note: Setter function for property historyType.

See also historyType().

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