How do I update the notification text for a foreground service in Android?

Question

When you want to update a Notification set by startForeground(), simply build a new notication and then use NotificationManager to notify it.

The key point is to use the same notification id.

I didn't test the scenario of repeatedly calling startForeground() to update the Notification, but I think that using NotificationManager.notify would be better.

Updating the Notification will NOT remove the Service from the foreground status (this can be done only by calling stopForground );

Example:

private static final int NOTIF_ID=1;

@Override
public void onCreate (){
    this.startForeground();
}

private void startForeground() {
    startForeground(NOTIF_ID, getMyActivityNotification(""));
}

private Notification getMyActivityNotification(String text){
    // The PendingIntent to launch our activity if the user selects
    // this notification
    CharSequence title = getText(R.string.title_activity);
    PendingIntent contentIntent = PendingIntent.getActivity(this,
            0, new Intent(this, MyActivity.class), 0);

    return new Notification.Builder(this)
            .setContentTitle(title)
            .setContentText(text)
            .setSmallIcon(R.drawable.ic_launcher_b3)
            .setContentIntent(contentIntent).getNotification();     
}

/**
 * This is the method that can be called to update the Notification
 */
private void updateNotification() {
    String text = "Some text that will update the notification";

    Notification notification = getMyActivityNotification(text);

    NotificationManager mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    mNotificationManager.notify(NOTIF_ID, notification);
}

The documentation states

To set up a notification so it can be updated, issue it with a notification ID by calling NotificationManager.notify(). To update this notification after you've issued it, update or create a NotificationCompat.Builder object, build a Notification object from it, and issue the Notification with the same ID you used previously. If the previous notification is still visible, the system updates it from the contents of the Notification object. If the previous notification has been dismissed, a new notification is created instead.

I would think that calling startForeground() again with the same unique ID and a Notification with the new information would work, though I have not tried this scenario.

Update: Based on the comments, you should use NotifcationManager to update the notification and your service continues to stay in the foreground mode. Take a look at the answer below.

Improving on Luca Manzo answer in android 8.0+ when updating the notification it will make sound and show as Heads-up.
to prevent that you need to add setOnlyAlertOnce(true)

so the code is:

private static final int NOTIF_ID=1;

@Override
public void onCreate(){
        this.startForeground();
}

private void startForeground(){
        startForeground(NOTIF_ID,getMyActivityNotification(""));
}

private Notification getMyActivityNotification(String text){
        if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O){
        ((NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE)).createNotificationChannel(
        NotificationChannel("timer_notification","Timer Notification",NotificationManager.IMPORTANCE_HIGH))
}

        // The PendingIntent to launch our activity if the user selects
        // this notification
        PendingIntent contentIntent=PendingIntent.getActivity(this,
        0,new Intent(this,MyActivity.class),0);

        return new NotificationCompat.Builder(this,"my_channel_01")
        .setContentTitle("some title")
        .setContentText(text)
        .setOnlyAlertOnce(true) // so when data is updated don't make sound and alert in android 8.0+
        .setOngoing(true)
        .setSmallIcon(R.drawable.ic_launcher_b3)
        .setContentIntent(contentIntent)
        .build();
}

/**
 * This is the method that can be called to update the Notification
 */
private void updateNotification(){
        String text="Some text that will update the notification";

        Notification notification=getMyActivityNotification(text);

        NotificationManager mNotificationManager=(NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
        mNotificationManager.notify(NOTIF_ID,notification);
}

here's the code to do so in your service. Create a new notification, but ask notification manager to notify the same notification id you used in startForeground.

Notification notify = createNotification();
final NotificationManager notificationManager = (NotificationManager) getApplicationContext()
    .getSystemService(getApplicationContext().NOTIFICATION_SERVICE);

notificationManager.notify(ONGOING_NOTIFICATION, notify);

for full sample codes, you can check here:

https://github.com/plateaukao/AutoScreenOnOff/blob/master/src/com/danielkao/autoscreenonoff/SensorMonitorService.java