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I'm following a tutorial. I've created a new activity using a wizard. I get NullPointerException when attempting to call a method on Views obtained with findViewById() in my activity onCreate().

Activity onCreate():

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

    View something = findViewById(R.id.something);
    something.setOnClickListener(new View.OnClickListener() { ... }); // NPE HERE

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

Layout XML (fragment_main.xml):

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="packagename.MainActivity$PlaceholderFragment" >

    <View
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:id="@+id/something" />

</RelativeLayout>

12 Answers 11

up vote 66 down vote accepted

The tutorial is probably outdated, attempting to create an activity-based UI instead of the fragment-based UI preferred by wizard-generated code.

The view is in the fragment layout (fragment_main.xml) and not in the activity layout (activity_main.xml). onCreate() is too early in the lifecycle to find it in the activity view hierarchy, and a null is returned. Invoking a method on null causes the NPE.

The preferred solution is to move the code to the fragment onCreateView(), calling findViewById() on the inflated fragment layout rootView:

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

  View something = rootView.findViewById(R.id.something); // not activity findViewById()
  something.setOnClickListener(new View.OnClickListener() { ... });

  return rootView;
}

As a side note, the fragment layout will eventually be a part of the activity view hierarchy and discoverable with activity findViewById() but only after the fragment transaction has been run. Pending fragment transactions get executed in super.onStart() after onCreate().

upvote
  flag
findViewById part should be in onActivityCreated. – Nepster
upvote
  flag
@Nepster It can be but does not have to. – laalto
upvote
  flag
Sometime the activity is not yet attach to fragment. – Nepster
1 upvote
  flag
@Nepster And that's why calling findViewById() on rootView and not on activity. – laalto

Since you have declared your View in the fragment_main.xml,move that piece of code where you get the NPE in the onCreateView() method of the fragment. This should solve the issue.

Agreed, this is a typical error because people often don't really understand how Fragments work when they begin working on Android development. To alleviate confusion, I created a simple example code that I originally posted on Application is stopped in android emulator , but I posted it here as well.

An example is the following:

public class ContainerActivity extends FragmentActivity implements ExampleFragment.Callback
{
    @Override
    public void onCreate(Bundle saveInstanceState)
    {
        super.onCreate(saveInstanceState);
        this.setContentView(R.layout.activity_container);
        if (saveInstanceState == null)
        {               
             getSupportFragmentManager().beginTransaction()
                .add(R.id.activity_container_container, new ExampleFragment())
                .addToBackStack(null)
             .commit();
        }
        getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener()
        {
            public void onBackStackChanged()
            {
                int backCount = getSupportFragmentManager().getBackStackEntryCount();
                if (backCount == 0)
                {
                    finish();
                }
            }
        });
    }

    @Override
    public void exampleFragmentCallback()
    {
        Toast.makeText(this, "Hello!", Toast.LENGTH_LONG).show();
    }
}

activity_container.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <FrameLayout
        android:id="@+id/activity_container_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

ExampleFragment:

public class ExampleFragment extends Fragment implements View.OnClickListener
{
    public static interface Callback
    {
        void exampleFragmentCallback();
    }

    private Button btnOne;
    private Button btnTwo;
    private Button btnThree;

    private Callback callback;

    @Override
    public void onAttach(Activity activity)
    {
        super.onAttach(activity);
        try
        {
            this.callback = (Callback) activity;
        }
        catch (ClassCastException e)
        {
            Log.e(this.getClass().getSimpleName(), "Activity must implement Callback interface.", e);
            throw e;
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View rootView = inflater.inflate(R.layout.fragment_example, container, false);

        btnOne = (Button) rootView.findViewById(R.id.example_button_one);
        btnTwo = (Button) rootView.findViewById(R.id.example_button_two);
        btnThree = (Button) rootView.findViewById(R.id.example_button_three);

        btnOne.setOnClickListener(this);
        btnTwo.setOnClickListener(this);
        btnThree.setOnClickListener(this);
        return rootView;
    }

    @Override
    public void onClick(View v)
    {
        if (btnOne == v)
        {
            Toast.makeText(getActivity(), "One.", Toast.LENGTH_LONG).show();
        }
        else if (btnTwo == v)
        {
            Toast.makeText(getActivity(), "Two.", Toast.LENGTH_LONG).show();
        }
        else if (btnThree == v)
        {
            callback.exampleFragmentCallback();
        }
    }
}

fragment_example.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <Button
            android:id="@+id/example_button_one"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="30dp"
            android:text="@string/hello" 
            android:layout_marginLeft="20dp"
            android:layout_marginRight="20dp"/>

        <Button
            android:id="@+id/example_button_two"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@+id/example_button_one"
            android:layout_alignRight="@+id/example_button_one"
            android:layout_below="@+id/example_button_one"
            android:layout_marginTop="30dp"
            android:text="@string/hello" />

        <Button
            android:id="@+id/example_button_three"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@+id/example_button_two"
            android:layout_alignRight="@+id/example_button_two"
            android:layout_below="@+id/example_button_two"
            android:layout_marginTop="30dp"
            android:text="@string/hello" />

</RelativeLayout>

And that should be a valid example, it shows how you can use an Activity to display a Fragment, and handle events in that Fragment. And also how to communicate with the containing Activity.

1 upvote
  flag
This example uses the android-support-v4 library for FragmentActivity and the support fragment manager. – EpicPandaForce
1 upvote
  flag
an even more complete example is available at //allinonescript.com/questions/24840509/… – EpicPandaForce
1 upvote
  flag
Although you should use Otto for communication instead of callbacks, and use Butterknife to inject views. – EpicPandaForce
1 upvote
  flag

Try OnStart() method and just use

View view = getView().findViewById(R.id.something);

or Declare any View using getView().findViewById method in onStart()

Declare click listener on view by anyView.setOnClickListener(this);

upvote
  flag
For me this was useful because I was trying to access a sibling view inside a fragment's onCreateView, where the fragment was declared in xml. The sibling views were still null in onCreateView because the parent hadn't finished inflating, but in onStart they had :) – Daniel Wilson

Add the following in your activity_main.xml

<fragment
    android:id="@+id/myFragment"
    android:name="packagename.MainActivity$PlaceholderFragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >
</fragment>

in the posted code above in the question there is a problem : you are using R.layout.activity_main in oncreate method, but the xml files name is "fragment_main.xml" , means you are trying to get the view of fragment_main.xml file which is not being shown so it gives null pointer exception. change the code like :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_main);// your xml layout ,where the views are

    View something = findViewById(R.id.something);
    something.setOnClickListener(new View.OnClickListener() { ... }); // NPE HERE

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

You are trying to access UI elements in the onCreate() but , it is too early to access them , since in fragment views can be created in onCreateView() method. And onActivityCreated() method is reliable to handle any actions on them, since activity is fully loaded in this state.

I've got the same NullPointerException initializing a listener after calling findViewById onCreate and onCreateView methods.

But when I've used the onActivityCreated(Bundle savedInstanceState) {...} it works. So, I could access the GroupView and set my listener.

I hope it be helpful.

Try to shift your accessing views to the onViewCreated method of fragment because sometimes when you try to access the views in onCreate method they are not rendered at the time resulting null pointer exception.

 @Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
     View something = findViewById(R.id.something);
     something.setOnClickListener(new View.OnClickListener() { ... }); // NPE HERE

     if (savedInstanceState == null) {
           getSupportFragmentManager().beginTransaction()
            .add(R.id.container, new PlaceholderFragment()).commit();
    }
 }

The view "something" is in fragment and not in activity, so instead of accessing it in activity you must access it in the fragment class like

In PlaceholderFragment.class

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

View something = root .findViewById(R.id.something);
something.setOnClickListener(new View.OnClickListener() { ... });

return root;
}

You have to remember important thing is : NullPointerException occurs when you have declared your variable and trying to retreive its value before assigning value to it.

Use onViewCreated() Method whenever using or calling views from fragments.

override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
      View v = view.findViewById(R.id.whatever)
}

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