title: addTextChangedListener Null Pointer Exception
body: <p>Been looking at other questions but none of them solved my problem.</p>
  
  <p>I have an editText and I need to implement an addTextChangedListener to this field so i can update values of other text views in real time.</p>
  
  <pre><code>public class MainActivity extends ActionBarActivity {
  
  
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      EditText billText = (EditText)findViewById(R.id.billValue);
      billText.addTextChangedListener(new TextWatcher() {
  
          @Override
          public void onTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {
              // TODO Auto-generated method stub
  
          }
  
          @Override
          public void afterTextChanged(Editable arg0) {
              // TODO Auto-generated method stub
  
          }
  
          @Override
          public void beforeTextChanged(CharSequence arg0, int arg1,
                  int arg2, int arg3) {
              // TODO Auto-generated method stub
  
          }
  
  
      });
  </code></pre>
  
  <p>Anything wrong in my code that I may be missing?</p>