title: Why the getLine1Number() method is imperceptible in android
body: <p>Please see the following simple code. I want to display the <code>getLine1Number()</code> method in the <code>textView</code>, because the return value from the method is as <code>String</code>.
  But when I run the code in my device, the result is imperceptible.</p>
  
  <pre><code>public class MainActivity extends Activity {
  TextView textView;
  TelephonyManager telephonyManager;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
  textView = (TextView) findViewById(R.id.textView);
  telephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
  String s = telephonyManager.getLine1Number();
   textView.setText(s);}
   }
  </code></pre>
  
  <p>And</p>
  
  <pre><code> &lt;uses-permission android:name="android.permission.READ_PHONE_STATE"/&gt;
  </code></pre>