Qt Reference Documentation

Two-way Button Example


The Two-way button example shows how to use The State Machine Framework to implement a simple state machine that toggles the current state when a button is clicked.

 int main(int argc, char **argv)
     QApplication app(argc, argv);
     QPushButton button;
     QStateMachine machine;

The application's main() function begins by constructing the application object, a button and a state machine.

     QState *off = new QState();
     off->assignProperty(&button, "text", "Off");

     QState *on = new QState();
     on->assignProperty(&button, "text", "On");

The state machine has two states; on and off. When either state is entered, the text of the button will be set accordingly.

     off->addTransition(&button, SIGNAL(clicked()), on);
     on->addTransition(&button, SIGNAL(clicked()), off);

When the state machine is in the off state and the button is clicked, it will transition to the on state; when the state machine is in the on state and the button is clicked, it will transition to the off state.


The states are added to the state machine; they become top-level (sibling) states.


The initial state is off; this is the state the state machine will immediately transition to once the state machine is started.

     button.resize(100, 50);
     return app.exec();

Finally, the button is resized and made visible, and the application event loop is entered.


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