MainActivity.java

package com.ericliudeveloper.sharedbillhelper.ui.activity;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

import com.ericliudeveloper.sharedbillhelper.R;
import com.ericliudeveloper.sharedbillhelper.adapter.PagerAdapter;
import com.ericliudeveloper.sharedbillhelper.ui.fragment.BillListFragment;
import com.ericliudeveloper.sharedbillhelper.ui.fragment.MemberListFragment;
import com.ericliudeveloper.sharedbillhelper.util.Router;


public class MainActivity extends BaseActivity implements ViewPager.OnPageChangeListener {
    FloatingActionButton mFAB;
    View.OnClickListener createMemberClickListener, createBillClickListener;


    @Override
    protected int getSelfNavDrawerItem() {
        return R.id.nav_home;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.nav_drawer);
    }


    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        setupFloatActionButton();
    }

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
//        View decorView = getWindow().getDecorView();

      //  Sticky flag — This is the UI you see if you use the IMMERSIVE_STICKY flag,
      // and the user swipes to display the system bars. Semi-transparent bars
      // temporarily appear and then hide again. The act of swiping doesn't clear
      // any flags, nor does it trigger your system UI visibility change listeners,
      // because the transient appearance of the system bars isn't considered a UI visibility
      // change.



        // Note: Remember that the "immersive" flags only take effect if you use them in conjunction
        // with SYSTEM_UI_FLAG_HIDE_NAVIGATION, SYSTEM_UI_FLAG_FULLSCREEN, or both. You can just use
        // one or the other, but it's common to hide both the status and the navigation bar when
        // you're implementing "full immersion" mode.

//        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
//                | View.SYSTEM_UI_FLAG_FULLSCREEN
//                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
//        decorView.setSystemUiVisibility(uiOptions);
    }

    private void setupFloatActionButton() {
        mFAB = (FloatingActionButton) findViewById(R.id.fab);
        createBillClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Router.startActivity(MainActivity.this, EditBillActivity.class, null);
            }
        };

        createMemberClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
//                Intent intent = new Intent(MainActivity.this, EditMemberActivity.class);
//                startActivity(intent);
                Router.startActivity(MainActivity.this, EditMemberActivity.class, null);
            }
        };

        int currentPage = mViewPager.getCurrentItem();

        setupFABAccordingToPage(currentPage);

    }

    @Override
    protected void setupToolbar() {
        super.setupToolbar();
        getSupportActionBar().setDisplayShowTitleEnabled(true);
    }

    @Override
    protected void setupViewPager(ViewPager viewPager) {
        PagerAdapter pagerAdapter = new PagerAdapter(getFragmentManager());
        pagerAdapter.addFragment(new BillListFragment(), getString(R.string.bill));
        pagerAdapter.addFragment(new MemberListFragment(), getString(R.string.member));
        viewPager.setAdapter(pagerAdapter);
        viewPager.addOnPageChangeListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        setupFABAccordingToPage(position);
    }

    private void setupFABAccordingToPage(int position) {
        if (position == 0) {

            mFAB.setImageDrawable(getResources().getDrawable(R.drawable.ic_note_add_white_24dp));
            mFAB.setOnClickListener(createBillClickListener);
        }

        if (position == 1) {
            mFAB.setImageDrawable(getResources().getDrawable(R.drawable.ic_person_add_white_24dp));
            mFAB.setOnClickListener(createMemberClickListener);
        }
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
}