def execution_engine_model_changed(self, model, prop_name, info):
        """Active observation of state machine and show and hide widget. """
        if not self._view_initialized:
            return

        active_sm_id = rafcon.gui.singleton.state_machine_manager_model.state_machine_manager.active_state_machine_id
        if active_sm_id is None:
            # relieve all state machines that have no active execution and hide the widget
            self.disable()
        else:
            # observe all state machines that have an active execution and show the widget
            self.check_configuration()