c# - async/await bad practice under Android? -


currently porting existing c# windows 8 / ios app android (with xamarin).

i used lot of async/await file io, dialogs, network, etc…

what happens when app paused/suspended during await call? under windows , ios there 2 possibilities:

  • the app resumed later, if nothing had happened
  • the app terminated if memory low.

in both cases, there no memoy leak, there no changes in control flow.

however, under android, activity can destroyed , recreated while process stays alive. in understanding of async/await means:

  • an unclosed dialog wait forever, meaning objects accessible caller ("this", local variables etc.) stay in memory forever (memory leak)
  • when awaited network request finishes while former activity has been destroyed android, code after "await" (e.g. file write) collide because 2 running instances of activity exist.

are assumtions true? if yes, can done? (without making program complicated before of invention of async/await)

an android activity guaranteed call onpause before activity deactivated/destroyed , onresume when starts (see http://developer.android.com/training/basics/activity-lifecycle/index.html).

how if had cancellationtokensource available activity. in onpause can call cancel , use:

try {     // async code     ... } catch (operationcancelledexception e) { }

see http://msdn.microsoft.com/en-us/library/jj155759.aspx cancelling async tasks.

more suggestion definitive answer, hope helps.

edit:

when started introducing async/await code found zombie virus. once start asyncing find spreads throughout rest of code. may you've got lots of async calls same reason. there 2 rules follow:

  1. declare methods public async task foo() instead of public async void foo()
  2. don't block on async code

in own practice, i've discovered 2 places can break these general rules.

  1. if you're @ 'top' (i.e. ui) of code, there may places have declare code async void because delegate you're overriding takes void return type. typical example of button.click method.
  2. i had database call looked single value in database. if converted async, lots of code elsewhere have change. discovered if you're guaranteed, , mean guaranteed, @ 'bottom' of code, none of methods below 1 you're calling use async, can safely call .result on task. saved me asyncing half code unnecessarily.

hope helps.


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