QHistoryState Class

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.