Develop Reference

What's the difference between setContentIntent and setFullScreenIntent in Android?

It seems like both involve showing a notification and then the user can touch the notification to launch your activity.
https://developer.android.com/training/notify-user/build-notification
Every notification should respond to a tap, usually to open an
activity in your app that corresponds to the notification. To do so,
you must specify a content intent defined with a PendingIntent object
and pass it to setContentIntent().
https://developer.android.com/training/notify-user/time-sensitive
Use a full-screen intent only for the highest-priority alerts
where you have an associated activity that you would like to launch after the user
interacts with the notification.
So it seems like in both situations a notification shows that the user must interact with and then your activity is launched.

Multiple fullscreen android notifications at the same time not stacking

I am working on an android project that has an alarm clock like functionality.
I schedule an intentService for each alarm instance (fires at 9pm, for example.), this intentService builds the notification and displays it. The notification includes a fullScreenIntent, which works as expected and launches the activity. I use the following code to do this:
alarmActivityIntent = new Intent(this, AlarmActivity.class);
PendingIntent alarmActivityPendingIntent = PendingIntent.getActivity(this, alertSchedule.getIntentId(), alarmActivityIntent, PendingIntent.FLAG_CANCEL_CURRENT);
mBuilder.setFullScreenIntent(alarmActivityPendingIntent, true);
Notification mNotification = mBuilder.build();
mNotificationManager.notify(alertSchedule.getIntentId(), mNotification);
This works as expected when only one alarm is set to fire at a specific time, however if two alarms are set to fire at a specific time the behavior changes.
I want the first fullScreenIntent to start its activity, then when that activity finishes, show the next one. I believe I want to build up a task stack, and push these alarm intents onto it. However this is all new to me.
Is it possible to group these notifications?

If you are using the full screen Intent feature, you don't need to use an IntentService or a Notification at all. Just have the AlarmManager start your Activity when it fires.
You don't want to build a task stack, that is all too complicated. If you have multiple alarms that can fire at the same time, you can have the AlarmManager start the same Activity each time. Set the launch mode of this Activity to singleTop (in the manifest), so that if the Activity is already showing when the alarm fires, it will not create another instance of the Activity on top of the existing one, but instead will deliver the Intent by calling onNewIntent() on the existing instance of the Activity. In onNewIntent() you can save the data (extras) of the Intent in a queue that will be processed when the user finishes the currently shown Activity. To do that, just override onBackPressed() so that when the user presses the BACK button to finish the current Activity, you can check if there are any additional alarms waiting in the queue. If there are none, you can just call super.onBackPressed() to finish the Activity. If there is anything in the queue, you can remove the first element in the queue and display that in your Activity. Keep doing that until the queue is empty.

Android notification starting new instance of activity no matter what the launchMode and/or flags are set to

I've been doing a lot of research on this and I've hit a wall. I've read what seems like all of the material on this topic (inluding this, this, and this as well as the docs) and nothing is helping me in what I want to do.
Basically, in the case that the app is open on the user's phone, I just want a notification to redirect the user to the already-existing Activity in my app. I use a pattern like this:
private PendingIntent buildPendingIntentForNotification(String type) {
Intent resultIntent = new Intent(this, MainActivity.class);
resultIntent.setAction(Intent.ACTION_VIEW);
resultIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);// have tried without this and with Intent.FLAG_ACTIVITY_CLEAR_TOP
resultIntent.putExtra(CommonUtils.NOTIFICATION_TYPE, type);
PendingIntent resultPendingIntent = PendingIntent.getActivity(getApplicationContext(), 0, resultIntent, PendingIntent.FLAG_UPDATE_CURRENT);
return resultPendingIntent;
}
I've also tried declaring all 4 types of launchModes in the Android Manifest within the activity tag. No matter what I do, clicking on the notification (even if the app is the active foreground app on the screen and MainActivity is the active activity) always seems to restart the activity from onCreate. From what I can see during debugging, onDestroy is not called at any time between getting the notification and clicking on it. However, after the notification is clicked, onCreate is called and THEN onDestroy is called even though my activity is not being destroyed, which is very strange. I'm hoping someone can help me make sense of this because all of the launchMode and Intent.setFlags suggestions are not working for me. Thanks a lot!

Just for info's sake, here's the code I used to fix my problem (with credit to David's solution):
private PendingIntent buildPendingIntentForNotification(String type) {
Intent resultIntent = new Intent(this, MainActivity.class);
//resultIntent.setAction(Intent.ACTION_VIEW);
resultIntent.setAction(Intent.ACTION_MAIN);
resultIntent.addCategory(Intent.CATEGORY_LAUNCHER);
resultIntent.putExtra(CommonUtils.NOTIFICATION_TYPE, type);
PendingIntent resultPendingIntent = PendingIntent.getActivity(getApplicationContext(), 0, resultIntent, PendingIntent.FLAG_UPDATE_CURRENT);
return resultPendingIntent;
}

There are 2 ways of doing this:
Notification to restore a task rather than a specific activity?
Resume application and stack from notification
However, you may also be seeing this nasty Android bug.

You cannot control and cannot be sure about the state of your activities on the Android, meaning (in your context) you can only start an activity that has been paused not one that has been destroyed. The OS decides which activities will keep paused and which will destroy and you have no control over that. When your activity leaves the foreground successive callbacks are being invoked at undefined times and to the OS's
What you can simply do is to save your activity's instance state in the onPause() method (which we know for sure that will be called as soon as the activity leaves the foreground) and the on onCreate() you can restore the activity with the data as it previously was.
Note: If you have for example Activity A and activity B and you start activity B from within activity A, then on activity B's onCreate() method you can getIntent().getExtras()

Android - use of FLAG_ACTIVITY_NEW_TASK

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.

A Task in Android is a separate User workflow. If you mange to see the Homescreen sometime, that usually means you start a new one.
Remove the flag and it should work. if it does not, try using Single top.

Try the below code:
Intent resultIntent = new Intent(context, YourActivity.class);
resultIntent.setAction(Intent.ACTION_MAIN) resultIntent.addCategory(Intent.CATEGORY_LAUNCHER);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0,
resultIntent, 0);
.setContentIntent(pendingIntent)

Change notification intent in Android

I have a service that shows a notification that I wish that will be able to go to a specific activity of my app each time the user presses on it. Usually it would be the last one that the user has shown, but not always.
If the activity was started before, it should return to it, and if not, it should open it inside of the app's task, adding it to the activities tasks.
In addition, on some cases according to the service's logic, I wish to change the notification's intent so that it will target a different activity.
How do i do that? Is it possible without creating a new notification and dismissing the previous one? Is it also possible without creating a new task or an instance of an activity?

No it wouldn't be possible to change the Activity once you have sent the notification.
You can start an Activity on your task stack that is not a problem, check out the notification service in the tutorial here:
http://blog.blundell-apps.com/notification-for-a-user-chosen-time/
You have to set a pending intent on the notification:
// The PendingIntent to launch our activity if the user selects this notification
PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, SecondActivity.class), 0);
// Set the info for the view that shows in the notification panel.
notification.setLatestEventInfo(this, title, text, contentIntent);
You can see the pending intent takes a normal intent "new Intent(this, SecondActivity.class" so if you want specific behaviour (like bringing to the top instead of starting a new activity. Add the flags like you would normally to this intent. i.e. FLAG_ACTIVITY_REORDER_TO_FRONT (something like that)

Since platform version 11, you can build a notification using Notification.Builder. The v4 support library has an equivalent class NotificationCompat.Builder.
You can't change the Activity once you've sent the notification, but you can update the notification with a new Intent. When you create the PendingIntent, use the flag FLAG_CANCEL_CURRENT. When you send the new notification, use the ID of the existing notification when you call NotificationManager.notify().
Also, you should be careful how you start your app. The Status Bar Notifications guide tells you how to set up the back stack.