error Fragment already added when call setCurrentItem() in ViewPager

when i calling setCurrentItem() in view pager to switch between fragments, getting error Fragment already added in firs time . but after swipe view pager ,this code run correct

what is the problem?

public class AdapterViewPager extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

 public AdapterViewPager(FragmentManager manager) {


    public Fragment getItem(int position) {

            return mFragmentList.get(position);

    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);



In Activity



  java.lang.IllegalStateException: Fragment already added: FragmentTeacher{3a7d524 #2 id=0x7f0e00c8

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