title: findViewById() returns null when I call it in onCreate()
body: <p>I'm having a problem with the findViewById on my first android app. I'm trying to call this function but always return null.</p>
  
  <p>My app have 2 activities. In the second activity (activity_display_message) I have this code:</p>
  
  <pre><code>@Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_display_message);
  
      if (savedInstanceState == null) {
          getSupportFragmentManager().beginTransaction()
                  .add(R.id.container, new PlaceholderFragment())
                  .commit();
      }
  
      //Obtener el mensaje desde el intent en MainActivity
      Intent intent = getIntent();
      String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
  
      //Buscar el textview en la vista
      TextView textView = (TextView) findViewById(R.id.texto);
      textView.setText(message);
  }
  </code></pre>
  
  <p>And this is the fragment_display_message.xml</p>
  
  <pre><code>&lt;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:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
  android:paddingBottom="@dimen/activity_vertical_margin"
  tools:context="com.example.app.DisplayMessageActivity$PlaceholderFragment"&gt;
  
  &lt;TextView
      android:id="@+id/texto"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" /&gt;
  </code></pre>
  
  <p></p>
  
  <p>I don't know why it return NULL and generate a <code>NullPointerException</code> when I try to do a <code>setText()</code>. I'm calling the correct Id and declaring it on the XML too. And I'm calling the <code>setContextView()</code> on the <code>onCreate()</code>.</p>
  
  <p>Sorry if this question is too obvious (I think that I'm ignoring something obvious) but I'm new on android development.</p>
  
  <p>EDIT: Logcat error:</p>
  
  <pre><code>02-10 10:25:58.960    1031-1031/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
  Process: com.example.app, PID: 1031
  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.DisplayMessageActivity}: java.lang.NullPointerException
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
          at android.app.ActivityThread.access$800(ActivityThread.java:135)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
          at android.os.Handler.dispatchMessage(Handler.java:102)
          at android.os.Looper.loop(Looper.java:136)
          at android.app.ActivityThread.main(ActivityThread.java:5017)
          at java.lang.reflect.Method.invokeNative(Native Method)
          at java.lang.reflect.Method.invoke(Method.java:515)
          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
          at dalvik.system.NativeStart.main(Native Method)
   Caused by: java.lang.NullPointerException
          at com.example.app.DisplayMessageActivity.onCreate(DisplayMessageActivity.java:35)
          at android.app.Activity.performCreate(Activity.java:5231)
          at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
  </code></pre>
  
  <p>          </p>
  
  <h2>Edit:</h2>
  
  <p>Problem solved. Just need move the code from <code>onCreate()</code> to <code>onCreateView()</code> and edit the references.</p>
  
  <p><code>onCreate()</code> will be the default.</p>
  
  <pre><code>    @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_display_message);
  
      if (savedInstanceState == null) {
          getSupportFragmentManager().beginTransaction()
                  .add(R.id.container, new PlaceholderFragment())
                  .commit();
      }
  }
  </code></pre>
  
  <p>And the <code>onCreateView()</code> on <code>PlaceholderFragment</code>:</p>
  
  <pre><code>        @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
              Bundle savedInstanceState) {
          View rootView = inflater.inflate(R.layout.fragment_display_message, container, false);
  
          //Obtener el mensaje desde el intent en MainActivity
          Intent intent = getActivity().getIntent();
          String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
  
          //Buscar el textview en la vista
          TextView textView = (TextView) rootView.findViewById(R.id.texto);
          textView.setText(message);
  
          return rootView;
      }
  </code></pre>