Android 中fragment的调用多个fragment的冲突处理

public class FragmentControl {
private List fragments;
//单例模式
private static FragmentControl framentControl;
private FragmentControl(){
fragments = new ArrayList();
}
public synchronized static FragmentControl getInstance(){
if(framentControl == null){
framentControl = new FragmentControl();
}
return framentControl;
}

//对Fragment进行的操作public void fragmentChanged(Fragment f, FragmentManager fm) {    FragmentTransaction transaction = fm.beginTransaction();    if (fragments != null) {        for (Fragment fragment : fragments) {            transaction.hide(fragment);        }    }    if (!f.isAdded()) {        transaction.add(R.id.fl, f);    } else {        transaction.show(f);    }    fragments.add(f);    transaction.commit();}

}