ViewPager嵌套fragment

public class ViewpagerAdapter extends FragmentPagerAdapter {

    private ArrayList<Fragment> arrayList;

    public ViewpagerAdapter(@NonNull FragmentManager fm,ArrayList<Fragment> arrayList) {
        super(fm);
        this.arrayList=arrayList;
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        return arrayList.get(position);
    }

    @Override
    public int getCount() {
        return arrayList.size();
    }
}

   arrayList=new ArrayList<>();
       arrayList.add(new Fragment1());
       arrayList.add(new Fragment2());
       arrayList.add(new Fragment3());
       arrayList.add(new Fragment4());
       viewpagerAdapter= new ViewpagerAdapter(getSupportFragmentManager(),arrayList);
       viewpager.setAdapter(viewpagerAdapter);