Changing a textview above viewpager depending on what page?

Question

I have an activity that has 2 buttons (Previous, Next) and a text view in between the two. Below that is a viewpager.

I would like to change the textview to the title of whatever page they are on.

Here is the class where it all happens:

public class MyWorkout extends BaseActivity {

NonSwipeableViewPager vp;
TextView txtViewTitle;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_workout);
    mToolBar = activateToolbar();
    setUpNavigationDrawer();
    getSupportActionBar().setTitle("My Workout");

    Intent intent = getIntent();
    String workouttitle = intent.getStringExtra("workout");
    switch(workouttitle) {
        case "w29" : {
            getSupportActionBar().setTitle("My Workout - Workout 29");
            break;
        }
        case "w30" : {
            getSupportActionBar().setTitle("My Workout - Workout 30");
            break;
        }
    }

    Button btnPrev = (Button) findViewById(R.id.btnPrevious);
    Button btnNext = (Button) findViewById(R.id.btnNext);
    vp = (NonSwipeableViewPager) findViewById(R.id.view_pager);
    txtViewTitle = (TextView) findViewById(R.id.txtViewTitle);
    this.addPages(vp);

    //THIS IS WHAT I HAVE TRIED
    if (vp.getCurrentItem() == 0) {
        txtViewTitle.setText("Week One, Monday");
    }
    if (vp.getCurrentItem() == 1) {
        txtViewTitle.setText("Week One, Wednesday");
    }

    btnNext.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            MoveNext();
        }
    });

    btnPrev.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            MovePrevious();
        }
    });

}
public void MoveNext() {
    //it doesn't matter if you're already in the last item
    vp.setCurrentItem(vp.getCurrentItem() + 1);
}

public void MovePrevious() {
    //it doesn't matter if you're already in the first item
    vp.setCurrentItem(vp.getCurrentItem() - 1);
}

private void addPages(NonSwipeableViewPager pager) {
    MyFragPagerAdapter adapter = new MyFragPagerAdapter(getSupportFragmentManager());
    Intent intent = getIntent();
    String workout = intent.getStringExtra("workout");
    Bundle args = new Bundle();
    args.putString("workout", workout);

    Week1Mon week1MonFragment = new Week1Mon();
    week1MonFragment.setArguments(args);
    adapter.addPage(week1MonFragment);
    Week1Wed week1WedFragment = new Week1Wed();
    week1WedFragment.setArguments(args);
    adapter.addPage(week1WedFragment);
    Week1Fri week1Fri = new Week1Fri();
    week1Fri.setArguments(args);
    adapter.addPage(week1Fri);
    Week2Mon week2MonFragment = new Week2Mon();
    week2MonFragment.setArguments(args);
    adapter.addPage(week2MonFragment);
    Week2Wed week2WedFragment = new Week2Wed();
    week2WedFragment.setArguments(args);
    adapter.addPage(week2WedFragment);
    Week2Fri week2Fri = new Week2Fri();
    week2Fri.setArguments(args);
    adapter.addPage(week2Fri);

    pager.setAdapter(adapter);
}
}

The part I have tried:

if (vp.getCurrentItem() == 0) {
        txtViewTitle.setText("Week One, Monday");
    }
    if (vp.getCurrentItem() == 1) {
        txtViewTitle.setText("Week One, Wednesday");
    }

This sets the textview to Week One, Monday. Unfortunately it doesn't change when the user hits the Next button. I'm also hoping theres a better way, as I don't want to "assume" that the current item is that day of the week, because every week is different. I also need to figure out how to set the current page when the app is opened, because it saves the position is shared pref and I have to load it in the class above, and somehow set the page to a current page (preferably by the title)

Here is MyFragPagerAdapter:

public class MyFragPagerAdapter extends FragmentPagerAdapter {

ArrayList<Fragment> pages = new ArrayList<>();

public MyFragPagerAdapter(FragmentManager fm) {
    super(fm);
}

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

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

public void addPage(Fragment f) {
    pages.add(f);
}

@Override
public CharSequence getPageTitle(int position) {
    return pages.get(position).toString();
}
}

Thanks for any help, let me know if you need to see more code!

Answer 1

You can use,

viewPager.addOnPageChangeListener(new OnPageChangeListener() {
public void onPageScrollStateChanged(int state) {}
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}

public void onPageSelected(int position) {
    // Check if this is the page you want.
}});