使用FragmentPagerAdapter从主活动中调用片段方法

public class MyPagerAdapter extends FragmentPagerAdapter {
    private List<Fragment> fragmentList;

    public MyPagerAdapter(FragmentManager fragmentManager, List<Fragment> fragments) {
        super(fragmentManager);
        this.fragmentList = fragments;
    }

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

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

ViewPager viewPager = findViewById(R.id.viewPager);
List<Fragment> fragments = new ArrayList<>();
fragments.add(new Fragment1());
fragments.add(new Fragment2());
fragments.add(new Fragment3());

MyPagerAdapter pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), fragments);
viewPager.setAdapter(pagerAdapter);

int currentPosition = viewPager.getCurrentItem();
Fragment currentFragment = pagerAdapter.getItem(currentPosition);

currentFragment.someMethod();