Got your reply late for some reason. I would agree with
onSaveInstanceState being called whenever you are put into a killable
state as it's the only thing that makes sense. As it turns out I am
just about to do some tests with the logging you suggested. If this is
the case it's a poor design IMHO. If you have a simulation that
requires a fair amount of serialization to save it's state it's not
going to work all that well.
The Android way seems to suggest that you make an Activity per full
screen and use the stack. So when I push an Activity for something like
my game options, I am forced to serialize my state if
onSaveInstanceState comes calling when the common case will be that the
user comes right back. If I wrote code at work with comments like it
may or may not be called, they would likely tell me to enjoy my new job.
Leigh
On 6/6/2010 9:30 PM, Daniel M. Drummond wrote:
On Sun, 2010-06-06 at 18:18 -0700, Leigh McRae wrote:
I am having a really hard time grokking the Activity life cycle
concept. The main issue is with onStop() and onDestory() not being
guaranteed to be called before the process is killed. I though I had
it figured out when I saw that the system calls onSaveInstanceState()
when it's shutting down the activity to claim some memory. Thing is
that the docs says onSaveInstanceState() will be called before
onPause() but how does the system know at this point whether the
activity will be killed by the system or the user?
Here is a use case:
1) My activity starts up and is running.
2) At some point I want to show a web page so I use an Intent to start
an activity.
3) The web browser covers my app/activity so I would expect onPause()
to be called followed by onStop().
At this point it's my understanding that all bets are off and I can be
killed at any point without be called.
4) Since the system has enough memory onSaveInstance() doesn't get
called.
5) The user presses home and decides to open some app which requires a
lot of memory.
6) System wants more memory and decides to kill my app but I am
already stopped (onPause() has been called). What happens here?
I am finding this a really serious problem since onPause() pretty much
needs to be treated as onDestory() as far as I can tell. If my app has
to be able to survive being killed without onStop() and onDestory()
being called, why bother having them?
From
http://developer.android.com/guide/topics/fundamentals.html#actlife
under the heading "Saving Activity State", we find
"Unlike onPause() and the other methods discussed earlier,
onSaveInstanceState() and onRestoreInstanceState() are not lifecycle
methods. They are not always called. For example, Android calls
onSaveInstanceState() before the activity becomes vulnerable to being
destroyed by the system, but does not bother calling it when the
instance is actually being destroyed by a user action (such as pressing
the BACK key). In that case, the user won't expect to return to the
activity, so there's no reason to save its state.
"Because onSaveInstanceState() is not always called, you should use it
only to record the transient state of the activity, not to store
persistent data. Use onPause() for that purpose instead."
So the way I understand it is that onSaveInstanceState() is called
whenever the *system* is putting the activity into a "killable" state,
thus allowing you to save the current state for it to be reloaded when
your activity is loaded again, but if the activity is being destroyed by
a user action, (where there is no expectation of an unchanged state) if
you want to save any state, you need to do it yourself in onPause().
So in your use case onSaveInstanceState() *will* be called, and the
state can be saved, so 4) is completely incorrect.
Feel free to correct me if I am wrong
Hope that helps
Dan
--
Leigh McRae
www.lonedwarfgames.com
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