title: How to use Elapsed Real Time in Android?
body: <p>I want to develop an app. The app has a spinner dropdown. The dropdown has 3 option (30min, 1h, 2h). When for example 30min is pressed I want to start an elapsed Real Time for 30min and after that I want to turn off wifi, that means after 30min the wifi should be turned off.</p>
  
  <p>The logcat shows me a NullPointer Exception.</p>
  
  <p>Here is my code</p>
  
  <pre><code>import android.app.Activity;
  import android.app.AlarmManager;
  import android.app.PendingIntent;
  import android.content.Intent;
  import android.os.SystemClock;
  import android.support.v7.app.ActionBarActivity;
  import android.view.View;
  import android.widget.AdapterView;
  import android.widget.Toast;
  
  public class SpinnerTimeOnItemSelectedListener extends Activity implements AdapterView.OnItemSelectedListener {
  
      @Override
      public void onItemSelected(AdapterView&lt;?&gt; parent, View view, int position, long 
          if(parent.getItemAtPosition(position).toString().equals("Zeit auswählen") || parent.getItemAtPosition(position).toString().equals("Select Time")){
              onNothingSelected(parent);
          } else if (parent.getItemAtPosition(position).toString().equals("30min")){
              Intent intent = new Intent(SpinnerTimeOnItemSelectedListener.this, ConnectionManager.class);
              PendingIntent pendingIntent = PendingIntent.getBroadcast(SpinnerTimeOnItemSelectedListener.this, 0, intent, 0);
              long firstTime = SystemClock.elapsedRealtime();
              AlarmManager am = (AlarmManager)getSystemService(ALARM_SERVICE);
              am.setRepeating(AlarmManager.ELAPSED_REALTIME, firstTime, 5000, pendingIntent);
          }
      }
  
      @Override
      public void onNothingSelected(AdapterView&lt;?&gt; parent) {
          // Wenn es einen ElapsedRealTimeAlarm gibt, soll er gecancelt werden
          // Ansonsten nichts
          ;
      }
  
  import android.content.BroadcastReceiver;
  import android.content.Context;
  import android.content.Intent;
  import android.widget.Toast;
  </code></pre>
  
  <p>And in this class the wifi should be managed (turned on/off)</p>
  
  <pre><code>public class ConnectionManager extends BroadcastReceiver {
  
      /**
       *
       * @param context The Context in which the receiver is running.
       * @param intent  The Intent being received.
       */
      @Override
      public void onReceive(Context context, Intent intent) {
          Toast.makeText(context, "I'm running", Toast.LENGTH_SHORT).show();
      }
  }
  </code></pre>
  
  <p>Error of the logcat:</p>
  
  <pre><code>07-24 17:35:17.503    5430-5430/com.falkenherz.abusufean.batterycooler E/AndroidRuntime﹕ FATAL EXCEPTION: main
  Process: com.falkenherz.abusufean.batterycooler, PID: 5430
  java.lang.NullPointerException
          at android.content.ContextWrapper.getContentResolver(ContextWrapper.java:104)
          at android.app.PendingIntent.getService(PendingIntent.java:522)
          at com.example.ali.turnoffwifi.SpinnerTimeOnItemSelectedListener.onItemSelected(SpinnerTimeOnItemSelectedListener.java:42)
          at android.widget.AdapterView.fireOnSelected(AdapterView.java:956)
          at android.widget.AdapterView.access$200(AdapterView.java:49)
          at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:920)
          at android.os.Handler.handleCallback(Handler.java:733)
          at android.os.Handler.dispatchMessage(Handler.java:95)
          at android.os.Looper.loop(Looper.java:157)
          at android.app.ActivityThread.main(ActivityThread.java:5356)
          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:1265)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
          at dalvik.system.NativeStart.main(Native Method)
  </code></pre>
  
  <p>The error is on this line:</p>
  
  <pre><code>PendingIntent pendingIntent = PendingIntent.getBroadcast(SpinnerTimeOnItemSelectedListener.this, 0, intent, 0);
  </code></pre>
  
  <p>How can I fix this problem?
  Thanks</p>