QStateMachine with RestoreProperty is losing property on transition

Question

The Qt documentation for State machines shows two principles I'm using: Restoring Properties and Targetless transitions. The first allows to assign properties to a QState, the second to trigger events only in a specific state.

When I combine both functions, restoring properties is not working anymore. When a QSignalTransition is fired, the properties are set to their initial values (before the state machine was started), even if the current state is not left.

I have a short example to reproduce this:

#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QVBoxLayout>
#include <QStateMachine>
#include <QSignalTransition>

int main(int argc, char *argv[]) {
  QApplication a(argc,argv);
  QWidget *w = new QWidget;

  QStateMachine *machine = new QStateMachine(w);
  QState *s1 = new QState;
  QState *s2 = new QState;

  QVBoxLayout *layout = new QVBoxLayout(w);
  QPushButton *btnState = new QPushButton("Not set");
  QPushButton *btnTrigger = new QPushButton("Trigger");
  layout->addWidget(btnState);
  layout->addWidget(btnTrigger);

  machine->setGlobalRestorePolicy(QStateMachine::RestoreProperties);

  s1->assignProperty(btnState,"text","S1");
  s2->assignProperty(btnState,"text","S2");

  s1->addTransition(btnState,SIGNAL(clicked()),s2);
  s2->addTransition(btnState,SIGNAL(clicked()),s1);

  QSignalTransition *sig = new QSignalTransition(btnTrigger,SIGNAL(clicked()));
  s1->addTransition(sig);

  machine->addState(s1);
  machine->addState(s2);
  machine->setInitialState(s1);

  machine ->start();

  w->show();
  return a.exec();
}

It has two buttons: The state button toggles between S1 and S2, the trigger button triggers a QSignalTransition when S1 is active. Clicking trigger when S1 is active, the button text will be set back to "Not set". If I understood the concept of setGlobalRestorePolicy() correctly, the property should stay "S1", as it is the value of the state S1, and the state was not left and is still active.

Is there something I missed or misunderstood, or did I something wrong?

I'm using Qt 4.8.4 on windows, if this makes any difference.

QStateMachine with RestoreProperty is losing property on transition

0 Answers0