Qt Reference Documentation

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# QHistoryState Class Reference

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

     #include <QHistoryState>

Inherits: QAbstractState.

This class was introduced in Qt 4.6.

- List of all members, including inherited members

## Public Types

enum | HistoryType { ShallowHistory, DeepHistory }

## Properties

- defaultState : QAbstractState *
- historyType : HistoryType

- 1 property inherited from QObject

## 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 )

- 2 public functions inherited from QAbstractState
- 29 public functions inherited from QObject

## Reimplemented Protected Functions

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

- 3 protected functions inherited from QAbstractState
- 8 protected functions inherited from QObject

### Additional Inherited Members

- 1 public slot inherited from QObject
- 2 signals inherited from QAbstractState
- 1 signal inherited from QObject
- 7 static public members inherited from QObject
- 3 protected functions inherited from QAbstractState
- 8 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.

Constant | Value | Description
--- | --- | ---
`QHistoryState::ShallowHistory` | `0` | Only 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::DeepHistory` | `1` | Nested 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 )

### 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 )

## 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.

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

Reimplemented from QObject::event().

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

Reimplemented from QAbstractState::onEntry().

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

Reimplemented from QAbstractState::onExit().