title: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
body: <p>I have a <code>BlankFragment</code></p>
  
  <pre><code>package com.hfad.addingafragmenttoframelayout;
  
  
  import android.os.Bundle;
  import android.support.v4.app.Fragment;
  import android.util.Log;
  import android.view.LayoutInflater;
  import android.view.View;
  import android.view.ViewGroup;
  import android.widget.TextView;
  
  import org.w3c.dom.Text;
  
  
  /**
   * A simple {@link Fragment} subclass.
   */
  public class BlankFragment extends Fragment {
  
  
      public BlankFragment() {
          // Required empty public constructor
      }
  
  
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
                               Bundle savedInstanceState) {
          Log.d("message","onCreateView() of BlankFragment");
          // Inflate the layout for this fragment
          return inflater.inflate(R.layout.fragment_blank, container, false);
      }
  
      public void setText(String textToBeSet){
          TextView tv = (TextView)this.getView().findViewById(R.id.fragmentText);
          tv.setText(textToBeSet);
      }
  
  }
  </code></pre>
  
  <p>and it's layout is:</p>
  
  <pre><code>&lt;FrameLayout 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"
      tools:context="com.hfad.addingafragmenttoframelayout.BlankFragment"&gt;
  
      &lt;!-- TODO: Update blank fragment layout --&gt;
      &lt;TextView
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:text="@string/hello_blank_fragment"
          android:id="@+id/fragmentText"/&gt;
  
  &lt;/FrameLayout&gt;
  </code></pre>
  
  <p>Here is the <code>MainActivity</code></p>
  
  <pre><code>package com.hfad.addingafragmenttoframelayout;
  
  import android.support.v7.app.AppCompatActivity;
  import android.os.Bundle;
  import android.view.View;
  import android.widget.TextView;
  
  public class MainActivity extends AppCompatActivity {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
  
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          //BlankFragment bf = new BlankFragment();
          //getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, bf).commit();
  
          BlankFragment bf = new BlankFragment();
          bf.setText("hello world");
          getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, bf).commit();
  
  
      }
  
  
  
  
  }
  </code></pre>
  
  <p>and here is the layout of <code>MainActivity</code></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout 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="com.hfad.addingafragmenttoframelayout.MainActivity"
      android:orientation="vertical"&gt;
  
      &lt;FrameLayout
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:id="@+id/fragment_container"
          /&gt;
  
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>In the onCreate method of activity I am adding fragment to layout. This works fine unless I try to change the Text using setText method. </p>
  
  <p>And I get this error:</p>
  
  <pre><code>Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
                                                                                             at com.hfad.addingafragmenttoframelayout.BlankFragment.setText(BlankFragment.java:35)
                                                                                             at com.hfad.addingafragmenttoframelayout.MainActivity.onStart(MainActivity.java:29)
  </code></pre>
  
  <p>referring to this line</p>
  
  <pre><code>TextView tv = (TextView)this.getView().findViewById(R.id.fragmentText);
  </code></pre>
  
  <p>Can somebody explain what's causing this exception?</p>