NewPipe/app/src/main/java/org/schabi/newpipe/fragments/MainFragment.java

package org.schabi.newpipe.fragments;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBar;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import org.schabi.newpipe.BaseFragment;
import org.schabi.newpipe.R;
import org.schabi.newpipe.fragments.subscription.SubscriptionFragment;
import org.schabi.newpipe.util.NavigationHelper;

public class MainFragment extends BaseFragment implements TabLayout.OnTabSelectedListener {
    private ViewPager viewPager;

    /*//////////////////////////////////////////////////////////////////////////
    // Fragment's LifeCycle
    //////////////////////////////////////////////////////////////////////////*/

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    @Override
    protected void initViews(View rootView, Bundle savedInstanceState) {
        super.initViews(rootView, savedInstanceState);

        TabLayout tabLayout = rootView.findViewById(R.id.main_tab_layout);
        viewPager = rootView.findViewById(R.id.pager);

        /*  Nested fragment, use child fragment here to maintain backstack in view pager. */
        PagerAdapter adapter = new PagerAdapter(getChildFragmentManager());
        viewPager.setAdapter(adapter);
        viewPager.setOffscreenPageLimit(adapter.getCount());

        tabLayout.setupWithViewPager(viewPager);
    }

    /*//////////////////////////////////////////////////////////////////////////
    // Menu
    //////////////////////////////////////////////////////////////////////////*/

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        if (DEBUG) Log.d(TAG, "onCreateOptionsMenu() called with: menu = [" + menu + "], inflater = [" + inflater + "]");
        inflater.inflate(R.menu.main_fragment_menu, menu);

        ActionBar supportActionBar = activity.getSupportActionBar();
        if (supportActionBar != null) {
            supportActionBar.setDisplayShowTitleEnabled(false);
            supportActionBar.setDisplayHomeAsUpEnabled(false);
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_search:
                NavigationHelper.openSearchFragment(getFragmentManager(), 0, "");
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /*//////////////////////////////////////////////////////////////////////////
    // Tabs
    //////////////////////////////////////////////////////////////////////////*/

    @Override
    public void onTabSelected(TabLayout.Tab tab) {
        viewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(TabLayout.Tab tab) {
    }

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

    private class PagerAdapter extends FragmentPagerAdapter {

        private int[] tabTitles = new int[]{
                R.string.tab_main,
                R.string.tab_subscriptions
        };

        PagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
                case 1:
                    return new SubscriptionFragment();
                default:
                    return new BlankFragment();
            }
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return getString(this.tabTitles[position]);
        }

        @Override
        public int getCount() {
            return this.tabTitles.length;
        }
    }
}