I have created a simple application having a button. Clicking it triggers a notification, and clicking on the notification launches a new instance of the same application. However, I wanted that clicking on the notification should bring me back to the application instance from which the notification was triggered. For this I consulted the Android docs for the FLAG_ACTIVITY_NEW_TASK flag-
When using this flag, if a task is already running for the activity you are now starting, then a new activity will not be started; instead, the current task will simply be brought to the front of the screen with the state it was last in. See FLAG_ACTIVITY_MULTIPLE_TASK for a flag to disable this behavior.
Based on this when creating the intent for passing to the PendingIntent, i set this flag. However, clicking on the notification still launches a new instance of the application.
What am I doing wrong ?
Remember that when you click the Notification it is from that Context that the intent is being launched. That context doesn't have the Activity on it's task (infact, it will be a blank task).
What this results in is two version of the same Activity (although still only one instance of you Application) running. Each Activity is running a different Task.
If you don't need duplicate Activities of the same type in any of your stacks you could use the answer here:
https://stackoverflow.com/a/2327027/726954
Otherwise, there are many ways to "fix" this problem, including singleton variables and Application Context methods that keeps track of which Activities are in a Running state.
You may need to search and refine your question for those.