Re: [android-developers] Re: Handling process killed by system

I think the documentation intentionally stays abstract on what happens
when the process is killed. I agree it's sort of strange this isn't
explained better, but in reality using statics in Android is usually a
bad idea for the reasons that have been described.

I agree with Piren, you should serialize state inside some other
facility unless you want to roll your own persistence code.

Kris

On Mon, Jun 24, 2013 at 5:08 AM, Benoit Vermont <redwarp@gmail.com> wrote:
> Well, I agree that using a singleton is a mistake. But, I think that the
> documentation is rather shallow, and should maybe explain the "process being
> killed" behavior more thoroughly. I mean, when you read the documentation,
> nothing let you guess that your singletons will be deleted, while the stack
> of activity and bundles are saved. (If it's said anywhere, I still havent
> found it).
>
> I will rewrite everything for persistance, but still think it would be best
> if the documentation explained a bit more...
>
>
> --
> Benoit Vermont
>
>
> 2013/6/23 Piren <gpiren@gmail.com>
>>
>> Seems to me your mistake is storing the information as a singleton... why
>> save everything in memory where it is volatile? store everything in a
>> database and you wouldn't have to worry about it being gone or using too
>> much memory. There's no reason to limit the user's ability to complete an
>> order to the current instance of the app... and then make a complex
>> workaround to allow the information to traverse instances.
>>
>>
>> On Friday, June 21, 2013 5:25:33 PM UTC+3, Benoit Vermont wrote:
>>>
>>> Hi, I've been reading intensively the Android Application Framework FAQ
>>> (http://developer.android.com/guide/faq/framework.html) and it says that the
>>> system can kill process if needed to free memory.
>>>
>>> Well, fair enough, only it also destroys singletons and static instances.
>>> So when we launch the application back after that, it tries to restore
>>> itself, but fails miserably because all static singletons are no more
>>> available.
>>>
>>> What bugs me is that the same documentation (Framework FAQ) specifically
>>> says : "You can take advantage of the fact that your application components
>>> run in the same process through the use of a singleton. This is a class that
>>> is designed to have only one instance. It has a static method with a name
>>> such as getInstance() that returns the instance; the first time this method
>>> is called, it creates the global instance. Because all callers get the same
>>> instance, they can use this as a point of interaction. For example activity
>>> A may retrieve the instance and call setValue(3); later activity B may
>>> retrieve the instance and call getValue() to retrieve the last set value."
>>>
>>> But it's not so true, as these singletons are not reliable at all.
>>>
>>> I mainly use singleton in my apps to store session variable. But some of
>>> this variables are quite complex (it can be information about the user,
>>> trees of object, etc). For exemple, I'm working on an ordering application
>>> that stores in a singleton a map of stuff the user wan't to buy. This maps
>>> is complex, it could also store information such as "what kind of shipping
>>> option does the user want", etc...
>>>
>>> But let's say I start the app on a cheap device (with low memory), I
>>> start shopping, but I then receive a call from a friend, I hang up, then I
>>> forget what I was doing, and launch Angry Birds, and then "hey, that's
>>> right, I was buying stuff", etc... I go back to the application, and the
>>> singletons don't exist anymore.
>>>
>>> Okay, looks like it's a bad idea to use static. But the FAQ is
>>> misleading, is it not ? The singletons are not really persistant : Once the
>>> order is finished, they are gonna be destroyed straight away.
>>>
>>> I guess that if running the app on api level 14 or more, I could use the
>>> onTrimMemory method from the Application class
>>> (http://developer.android.com/reference/android/app/Application.html#onTrimMemory(int))
>>> to save/serialize my singleton there, and when the application is
>>> relaunched, and the singleton is null, restore it.
>>>
>>> But what would be the good/best/not so sucky way to handle with
>>> not-really-persistant-but-it-might-be-nice-to-exist-one-hour kind of object
>>> ?
>>>
>>> Thanks.
>>
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