在暂停状态下完成活动，但仍处于后退状态？

Question

I'm trying to minimize memory usage in my app, and one of the things I'm doing is calling finish() in the onPause method (which I know is not the best way to do things). For the most part, it seems to be working well, but when the user clicks the back button from the next activity, it logically skips over the finished activity and goes back further. Is it possible to have that activity in the back stack and just get recreated if the user presses back?

Answer 1

No. This conclusion comes from the task and backstack documentation as well as the activity documentation and a general understanding of how a stack data structure works.

A stack data strucure only has 2 possible operations push/put, which adds something to the collection, and pop, which removes it. Stacks folow a last in first out model, or LIFO, where by last thing added - in your case an activity - is the first thing removed when pop is called.

Within the android lifecycle activities are generally popped from the stack when the back button is pressed. At that point onDestroy() is called and the activity is removed (you can verify this by overriding the onDestroy() method and logging the results if you want to check). Alternativly you can force onDestroy() to be called by calling finish() as you are. Finishing an activity effectivly does the same thing as pressing back. The activity is destroyed and must be recreated before it can be added to the stack.

For what you're trying to do the stack would have to incorporate some intermediate state in which an activity does not exist but rather something akin to a reference is held that, when moved to the top, would indicate that the corresponding activity should be recreated. Since this is not how the sack works - it only holds activities - that state cannont exist and so the result you are talking about is not possible.

Answer 2

Your Goal is to minimize memory usage,Just make use of activity life cycle , You can do this alternative(if you need)

-Just leave onCreate() method blank.(only do setContentView(layout))

-Override onResume() ;

-whatever you were doing in onCreate just copy paste to onResume().

-and In onPause() , Recycle your all bitmaps and set them to null(I think you are using Bitmaps thats why you are very cautious about it ). and remove your views.

Now what will happen, when you launch your new activity, onPause() would be called. that will remove your all bitmap and views. and when you come back, onResume() will be call.(onCreate will not be called). and that will again initialize your view and bitmaps.

Answer 3

No, i don't think that is possible. Once you finish the Activity it's gone. You could, however, implement and handle your own stack. On back pressed, you would just start the closed Activity again.