As per the documentation of FLAG_ACTIVITY_MULTIPLE_TASK:
This flag is used to create a new task and launch an activity into it.
This flag is always paired with either FLAG_ACTIVITY_NEW_DOCUMENT or FLAG_ACTIVITY_NEW_TASK. In both cases these flags alone would search through existing tasks for ones matching this Intent.This flag is ignored if one of FLAG_ACTIVITY_NEW_TASK or FLAG_ACTIVITY_NEW_DOCUMENT is not also set.
When paired with FLAG_ACTIVITY_MULTIPLE_TASK both of these behaviours are modified to skip the search for a matching task and unconditionally start a new task. When used with FLAG_ACTIVITY_NEW_TASK, a new task is always started to host the Activity for the Intent, regardless of whether there is already an existing task running the same thing.
Because the default system does not include graphical task management, you should not use this flag unless you provide some way for a user to return back to the tasks you have launched. See FLAG_ACTIVITY_NEW_DOCUMENT for details of this flag's use for creating new document tasks.
So this means that if I have an activity 1 which opens activity 2 with both of these flags, the 2 activities are opened in different stacks and are thus available as different tasks in recent.
However my question is to understand the behaviour of back button in this scenario. ideally when activities are launched without any flags, pressing back on them destroys the activity and it is removed from the backstack. if there are no activities, the system exits the app but keeps the backstack with the last activity. however in this case when i press back, 2 different beaviors are observed:
(Scenario: An app that launches Activity1 which launches Activity2 which launches Activity3 via startActivity(Intent(...).also{it.flags = FLAG_ACTIVITY_NEW_TASK or FLAG_ACTIVITY_MULTIPLE_TASK}) )
if i just press back on Activity 3 , i move to Activity 2 . similarly when i press back on Activity 2, i move to Activity 1. and finally when i press back on Activity 1, i exit the app . however, i can see all the activities remain in recents and available to be opened. when i open any of them and press back, then this time, i just get exited from the app into homescreen. video sample
if i press recents on any of the activities while traversing forward, the back-press stops working, and instead i get exited from any of the activity in recents. video sample
So :
- why is this behaviour?
- Can we assume that if there is just 1 activity in a back-stack, it will show up in recents and not get destroyed, unless the user explicitly clears it from the recents?
- Why Activities show a weak link to the caller activity in 1st case and going back to the parent back-stack when press back in 1st scenario?
