Viewpager loading all fragments?

Question

Android

Good morning, guys, I've been racking my brain for a day and I just can't figure out what the problem is.
At the bottom, I added the code, this one when it loads all the fragments at once, but I want it to be like this: The application opens, data is loaded only from "OneFragment", then scrolled through and loaded from "TwoFragment".
Tell me how to do it?
PagerAdapter.java

public class PagerAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;

    public PagerAdapter(FragmentManager fm, int NumOfTabs) {
        super(fm);
        this.mNumOfTabs = NumOfTabs;
    }

    @Override
    public Fragment getItem(int position) {

        switch (position) {
            case 0:
                OneFragment tab1 = new OneFragment();
                return tab1;
            case 1:
                TwoFragment tab2 = new TwoFragment();
                return tab2;
            default:
               return null;
        }
    }

    @Override
    public int getCount() {
        return mNumOfTabs;
    }
}

TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        tabLayout.addTab(tabLayout.newTab().setText("One"));
        tabLayout.addTab(tabLayout.newTab().setText("Two"));

        final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
        final PagerAdapter adapter = new PagerAdapter
                (getSupportFragmentManager(), tabLayout.getTabCount());
        viewPager.setAdapter(adapter);
        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.setOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(viewPager) {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                super.onTabSelected(tab);
                viewPager.setCurrentItem(tab.getPosition(), true);
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                super.onTabUnselected(tab);
                Log.d("fragmentpage", String.valueOf(tab.getPosition()));
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

Answer 1

by default the pager creates and stores 3 fragments, which is before the user, one before, one after.
this behavior can be changed by making setOffscreenPageLimit(int num)
but, I suppose, the interest is not idle? do you want to catch the event when the fragment appears in front of the user?