QActionGroup* action_group = new QActionGroup( this );
ui->action1->setCheckable(true);
ui->action2->setCheckable(true);
ui->action3->setCheckable(true);
ui->action1->setActionGroup(action_group);
ui->action2->setActionGroup(action_group);
ui->action3->setActionGroup(action_group);
QActionGroup is exculsive default. if you want they are checkbox, you must call setExculsive(false).
or you can first create the QActionGroup object, then call addAtion(QAction * ) to add actions into group.
that's all.