title: Android group notification does not alarm after adding summary notification (Android 6.0)
body: <p>I am trying to get local notifications to work like Hangouts. I would like a heads up notification to appear each time a new text message is received. But when there are two or more unread notifications I would like to display a summary notification in the Android notification bar. It seems like stacking notification via groups and adding a group summary should work as described <a href="http://developer.android.com/training/wearables/notifications/stacks.html" rel="nofollow">here</a>. The code below seems to work for me on Android 5.0 and 5.1, but on Android 6.0 the local notification does not alarm/display in heads up view when a summary notification for that group exists. So only the initial notification is displayed.</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  
  private Button _button = null;
  final static String GROUP_KEY_EMAILS = "group_key_emails";
  private int messageNum = 1;
  
  private void CreateNotification() {
      // Build the notification, setting the group appropriately
      Notification headsUpNotification = new NotificationCompat.Builder(this)
              .setContentTitle("Title")
              .setContentText("New Message" + messageNum)
              .setSmallIcon(R.drawable.pngreceivedtextmessage)
              .setGroup(GROUP_KEY_EMAILS)
              .setPriority(Notification.PRIORITY_HIGH)
              .setDefaults(Notification.DEFAULT_ALL)
              .build();
  
      // Issue the notification
      NotificationManagerCompat notificationManager =
              NotificationManagerCompat.from(this);
      notificationManager.notify(messageNum, headsUpNotification);
  
      Bitmap largeIcon = BitmapFactory.decodeResource(getResources(),
              R.drawable.pngreceivedmessageicon);
  
      if(messageNum &gt; 1) {
          // Create a summary notification since we have more than 1
          Notification summaryNotification = new NotificationCompat.Builder(this)
                  .setContentTitle("Summary")
                  .setNumber(messageNum)
                  .setSmallIcon(R.drawable.pngreceivedtextmessage)
                  .setLargeIcon(largeIcon)
                  .setGroup(GROUP_KEY_EMAILS)
                  .setGroupSummary(true)
                  .build();
  
          notificationManager.notify(0, summaryNotification);
      }
  
      messageNum++;
  }
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      _button = (Button) findViewById(R.id.button);
      _button.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              CreateNotification();
          }
      });
  }
  </code></pre>
  
  <p>I am targeting SDK 23 and have tried many different combination but nothing works. Does anyone know how to generate a summary notification and still get heads up notifications to work?</p>