Updating TextView in TabLayout causes NullPointerException

Question

I'm trying to create an app with 3 tabs, with each tab representing data that I receive from another device. I receive this data every 5 mins or so, so I need the text in the tabs to change constantly. However, I have trouble updating the TextView in the tabs to match the latest incoming data, as it causes a NullPointerException. Below is the main activity in which lies the issue:

public class PlantStatsActivity extends FragmentActivity {

public DrawerLayout mDrawerLayout;
public ListView mDrawerList;
private TabLayout tabLayout;
private ViewPager viewPager;
private ViewPageAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_plant_stats);
    initPubNub();


    tabLayout = (TabLayout) findViewById(R.id.tab_layout);
    tabLayout.addTab(tabLayout.newTab().setText("Moisture"));
    tabLayout.addTab(tabLayout.newTab().setText("Light"));
    tabLayout.addTab(tabLayout.newTab().setText("Temperature"));

    viewPager = (ViewPager) findViewById(R.id.pager);
    adapter = new ViewPageAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
    viewPager.setAdapter(adapter);

    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {

        @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) {

        }
    });

    LightFragment lightFragment = (LightFragment) adapter.getItem(1);
    lightFragment.setLightText("Test"); //This is where the problem lies.
}

I get a NullPointerException because the field lightTextis null (I'm just trying to get this to work on the "Light" tab, for now).

This the the fragment who's TextView I'm trying to update in the activity

public class LightFragment extends Fragment {
    private int lightLevel;
    private TextView lightText;

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View v = inflater.inflate(R.layout.fragment_light, container, false);
        lightText = (TextView) v.findViewById(R.id.current_level_light);
        return v;
    }

    public int getLightLevel() {
        return lightLevel;
    }

    public void setLightLevel(int newLightLevel){
        lightLevel = newLightLevel;
    }

    public TextView getLightText() {
        return lightText;
    }

    public void setLightText(String newText) {
        lightText.setText(newText); //Method used in activity causing crash.
    }

}

I'm including the ViewPageAdapter class:

public class ViewPageAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;

    public ViewPageAdapter(FragmentManager fm, int numOfTabs){
        super(fm);
        this.mNumOfTabs = numOfTabs;
    }

    @Override
    public Fragment getItem(int position){
        switch (position){
            case 0:
                MoistureFragment tab1 = new MoistureFragment();
                return tab1;
            case 1:
                LightFragment tab2 = new LightFragment();
                return tab2;
            case 2:
                TemperatureFragment tab3 = new TemperatureFragment();
                return tab3;
            default:
                return null;
        }
    }

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

}

Code that shows the process of receiving and handling data, which is a JSON object that stores an int value I'm interested in. Called at the beginning of the main activity.

public void initPubNub(){
    PNConfiguration pnConfiguration = new PNConfiguration();
    pnConfiguration.setPublishKey(PUBLISH_KEY);
    pnConfiguration.setSubscribeKey(SUBSCRIBE_KEY);
    pnConfiguration.setUuid("AndroidPiLight");
    mPubNub = new PubNub(pnConfiguration);
    mPubNub.subscribe().channels(Arrays.asList(CHANNEL)).execute();
    Log.d(TAG, "subscribed");

    mPubNub.addListener(new SubscribeCallback() {
        @Override
        public void status(PubNub pubnub, PNStatus status) {
            // handle any status
        }

        @Override
        public void message(PubNub pubnub, PNMessageResult message) {
            JsonNode lightNode = message.getMessage().findValue("lightValue"); // "lightValue" is JSON key.
            int newLight = lightNode.asInt();
            Log.d(TAG, "Got message as int");
            Bundle data = new Bundle();
            data.putInt("lightMessage", newLight);
            Message message1 = new Message();
            message1.setData(data);
            android.os.Handler handler = LightFragment.sUpdateHandler;
            if (handler != null){
                handler.sendMessage(message1);
            }

I'm a beginner to Android so I'm not really sure if I'm doing something wrong in the app, or if I need to add something totally different to make this work. I've looked thoroughly through previous questions of Stack Overflow, and could not find any answers. This is my first question on Stack Exchange, and any feedback is sincerely appreciated.

Answer 1

Try this in your pager adapter class do this

       LightFragment tab2 = new LightFragment();
        Bundle data = new Bundle();
        data.putInt("current_page", "id");
        data.putString("current_id","" );
        data.putInt("sub_cat_id","");
        myFragment.setArguments(data);

Then in your LightFragment class onCreate get this bundle value

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

    /** Getting the arguments to the Bundle object */
    Bundle data = getArguments();

    /** Getting integer data of the key current_page from the bundle */
    mCurrentPage = data.getInt("current_page", 0);

    }