NullPointerException accessing views in onCreate()

Question

This is a canonical question for a problem frequently posted on StackOverflow. I'm following a tutorial. I've created a new activity using a wizard. I get `NullPointerException` when attempting to call a method on `View`s 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_vertica…

Accepted Answer

The tutorial is probably outdated, attempting to create an activity-based UI instead of the fragment-based UI preferred by wizard-generated code.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

NullPointerException accessing views in onCreate()

Solution

Problem