Null pointer exception when calling addView(): Android

Question

I am trying to create a notepad app that has three tabs at the top, each linking to a different view.

The first two tabs will simply contain a form to fill out while the third will be where the actual writing is done. The problem is whenever I try to try to inflate this third view I am getting a null pointer exception for this line:

((LinearLayout) findViewById(R.id.drawRoot)).addView(v,0);

Here is my code:

public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    // When the given tab is selected, show the tab contents in the container
    Fragment fragment = new Section3Fragment();
    Bundle args = new Bundle();
    args.putInt(Section3Fragment.ARG_SECTION_NUMBER, tab.getPosition() + 1);
    fragment.setArguments(args);
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container3, fragment)
            .commit();
}


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


public  class Section3Fragment extends Fragment {
    public Section3Fragment() {
    }

    int section;
    public static final String ARG_SECTION_NUMBER = "section_number";

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

        Bundle args = getArguments();
       section = args.getInt(ARG_SECTION_NUMBER);
       View view;

       if (section == 1)
       {
            view = inflater.inflate(R.layout.section3_page1, container,false);

           return view;
       }
       if (section == 2){

        view = inflater.inflate(R.layout.section3_page2, container, false);
        return view;
       }
       else {


            if(v != null)
                Log.v("not null", "not null");

            view = inflater.inflate(R.layout.section3_page3, container, false);
            ((LinearLayout) findViewById(R.id.drawRoot)).addView(v,0); //null pointer exception here!!


           return view;

       }
    }
}

The object v is an instance on the class I use to do the actual drawing.

And the section3_page3 layout file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawRoot"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
</LinearLayout>

Any insight into this issue is greatly appreciated.

Can you paste here the exception message, please? Also in your code we can't see where v is initialized. — comprex
– comprex, Commented Jul 9, 2012 at 15:49

Blundell · Accepted Answer · 2012-07-09 15:47:34Z

2

At a quick glance, are you trying to do:

 ((LinearLayout) view.findViewById(R.id.drawRoot)).addView(v,0);

Your looking for the view on your fragment. not on the view you inflated within the if statement.

answered Jul 9, 2012 at 15:47

Blundell

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1 Comment

sean9898 Over a year ago

Yes, that was my problem. Thank you. I would have never figured that one out

Sam · Accepted Answer · 2012-07-09 15:55:47Z

1

You posted section3_page3.xml but you open inflater.inflate(R.layout.section3_page2, container, false). Is this a typo or the root cause of your problem?

Opening the wrong XML file will cause findViewById() to return null here:

view = inflater.inflate(R.layout.section3_page2, container, false);
((LinearLayout) findViewById(R.id.drawRoot)).addView(v,0);

Hence a NullPointerException... I'm guessing you meant:

view = inflater.inflate(R.layout.section3_page3, container, false);
((LinearLayout) findViewById(R.id.drawRoot)).addView(v,0);

edited Jul 9, 2012 at 15:55

answered Jul 9, 2012 at 15:47

Sam

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1 Comment

sean9898 Over a year ago

That was a typo, I apologize. it should have been R.layout.section3_page3

t0mm13b · Accepted Answer · 2012-07-09 15:57:31Z

1

Since you're using the ActionBar, and Fragments, I suggest changing this:

((LinearLayout) findViewById(R.id.drawRoot)).addView(v,0);

into this:

((LinearLayout) getActivity().findViewById(R.id.drawRoot)).addView(v,0);

answered Jul 9, 2012 at 15:57

t0mm13b

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