android - Starting Activity through notification: Avoiding duplicate activities

Question

So I am currently showing a notification. When the user clicks this noticiation, the application is started. The notification persists, to indicate that the service is running in the background.

Intent notificationIntent = new Intent(context, LaunchActivity.class);
PendingIntent contentIntent = PendingIntent.getActivity(context, 0, notificationIntent, 0);
notification.setLatestEventInfo(context, contentTitle, contentText, contentIntent);
mNotificationManager.notify(1, notification);

However, I have detected a case where a bug appears. If the user starts the application through clicking the normal icon, and while the activity is running clicks the notification, then a new activity is started without the earlier one exiting, the later being on top of the earlier. And that is not all: Further clicks on the notification will create additional activities and place them on top of those already running. How can I prevent this? Is there a nice check to do to see if a certain activity is currently being shown or is loaded?

Answer 1

That's the way it's supposed to be by default. You probably need to specify android:launchMode="singleTop" if you want to have a single instance only.
There are 4 launch modes, more info here: https://developer.android.com/guide/topics/manifest/activity-element.html