stepBackward method
Implementation
void stepBackward(Event event, StepDirective? step) {
// Prevent event from propagating up to the stepper. This
// is necessary for a vertical default sized stepper with
// all jumps allowed, so that the stepper doesn't jump back
// to the step after clicking the cancel button
event.preventDefault();
event.stopPropagation();
AsyncActionController<bool> ctrl = AsyncActionController<bool>();
step?.requestStepCancel(ctrl.action!);
ctrl.execute(() {
activeStep?.complete = false;
return _stepTo((activeStepIndex > 1) ? activeStepIndex - 1 : 0);
});
}