Null pointer errors in mainActivity for building swipe view with tabs on Android studios

Question

I am looking to build the swipe view with tabs function in my application by following a tutorial that I found on one of the answers in the forum

[http://www.androidhive.info/2013/10/android-tab-layout-with-swipeable-views-1/]

But I keep getting a null pointer error which I cant seem to find out why? I have strictly followed the tutorial and also read other similar questions about swipe views on forum. The coding are practically identical to what I have at the moment. But every time I run the emulator I get this error

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tim.swipe/com.example.tim.swipe.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActionBar$Tab android.app.ActionBar.newTab()' on a null object reference

I assume its something to do with the ActionBar but the codes from the tutorial and other sources are practically the same.

MainActivity.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener {



ViewPager viewPager;
TabsPagerAdapter adapter;
ActionBar actionBar;
String[] tabs =  { "FragmentA", "FragmentB", "FragmentC" };

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

    viewPager = (ViewPager) findViewById(R.id.pager);
    actionBar = getActionBar();
    adapter = new TabsPagerAdapter(getSupportFragmentManager());

    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }
}




@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

}

activity_main.xml

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent">

TabsPageAdapter.java

public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int i) {

    switch (i) {
        case 0:
            // Top Rated fragment activity
            return new FragmentA();
        case 1:
            // Games fragment activity
            return new FragmentB();
        case 2:
            // Movies fragment activity
            return new FragmentC();
    }
    return null;
}

@Override
public int getCount() {
    return 3;
}

FragmentA

public class FragmentA extends Fragment {


public FragmentA() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_a, container, false);

    return rootView;
}

FragmentB and FragmentC has the same code except for their layouts.

No i cant see what is in MainActivity because you haven't posted your code, post it please — Arlind Hajredinaj, Apr 04 '15 at 22:48

Arlind Hajredinaj · Answer 1 · 2015-04-04T23:29:58.340

0

Add this variable to the Class:

private TabsPagerAdapter mAdapter;

Change your onCreate method to this:

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

    viewPager = (ViewPager) findViewById(R.id.pager);
    actionBar = getActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

    viewPager.setAdapter(mAdapter);
    actionBar.setNavigationMode(actionBar.NAVIGATION_MODE_TABS);

    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }
}

edited Apr 04 '15 at 23:29

answered Apr 04 '15 at 22:57

Arlind Hajredinaj

8,380
3
30
45

It says error saying "Cannot resolve method 'getSupportActionBar();' – Timhua Apr 04 '15 at 23:02
I have added that but I still get the same error message. Also It says that setNavigationMode is deprecated. I am using API level 21 for compilation if that's of any help – Timhua Apr 04 '15 at 23:22
I have changed from **FragmentActivity** to**ActionBarActivity** and then used `actionBar = getSupportedActionBar();` This allowed the application to run which seems to have bypassed the java.lang null pointer problem. But now I have the problem where when swipe to a next fragment, the aciton bar on top doesn't change along with it. – Timhua Apr 05 '15 at 00:06

score 0 · Answer 2 · edited May 23 '17 at 11:43

0

I got this error too. Here is a solution it is works for me.

Add

getWindow().requestFeature(Window.FEATURE_ACTION_BAR);

Before

setContentView

Make sure that your Themes in Manifest that's support Action Bar.

Also make sure your Android minsdkversion above 11.

Hope this would work for you.

You can refer this original answer below.
Reference

edited May 23 '17 at 11:43

Community

1
1

answered Apr 09 '15 at 02:27

89030943809

157
1
1
16

Null pointer errors in mainActivity for building swipe view with tabs on Android studios

2 Answers2