Android destroying activities, killing processes

Question

Hi I\'m wondering how Android is managing memory and I can\'t find precise answer anywhere. Let\'s assume I have an application with 5 activities on current activity stack (

Answer 1

Can system destroy only one or some of my activities to recover memory?

Yes. Android kills activities which are running in the background when there is a need for memory. Killing one or all might depend on some conditions. For an instance paused or stopped can make android kill an activity or a process itself. Here under Activity Lifecycle you can get the below points. I recommend you to go through that page completely. It will definitely clear your doubts.

If an activity has lost focus but is still visible (that is, a new non-full-sized or transparent activity has focus on top of your activity), it is paused. A paused activity is completely alive (it maintains all state and member information and remains attached to the window manager), but can be killed by the system in extreme low memory situations.

If an activity is completely obscured by another activity, it is stopped. It still retains all state and member information, however, it is no longer visible to the user so its window is hidden and it will often be killed by the system when memory is needed elsewhere.

If an activity is paused or stopped, the system can drop the activity from memory by either asking it to finish, or simply killing its process. When it is displayed again to the user, it must be completely restarted and restored to its previous state.

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Will system kill the whole process of my application? Will all activities be nicely destroyed?

Activity pertains to an individual whereas process pertains to group of activities. Look at the third point above again it kills the process as mentioned.

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What will happen when I get back to my application when it was totally killed?

Its similar to restart . Again the third point will give you some answers like When it is displayed again to the user, it must be completely restarted and restored to its previous state

Get some more information about memory related stuffs here.

Edit:
All activities in an application runs in a single process. So when a process is killed all the activities no matter 5 or 10 will be killed i.e., restarted. Restart will cause your application to start from a beginning no saved states.