TabLayout中的Android片段如何读取自己的索引？

<android.support.design.widget.TabLayout
    android:id="@+id/tab_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:tabMode="fixed"
    app:tabGravity="fill"/>

<android.support.v4.view.ViewPager
    android:id="@+id/view_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

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

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

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

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

TabLayout tabLayout = findViewById(R.id.tab_layout);
ViewPager viewPager = findViewById(R.id.view_pager);

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);
tabLayout.setupWithViewPager(viewPager);

int index = getActivity().findViewById(R.id.view_pager).getCurrentItem();