I.e. that a coroutine launched in onStart will get cancelled in onStop, onCreateView -> onDestroyView, onCreate -> onDestroy; etc?

Usually you basically make your Activity/Fragment implement

CoroutineScope by MainScope()

and call

cancel()

in

onDestroy()

And how would that cancel onStart jobs in onDestroy?

If you started your job with just

launch { }

or something like that in

onStart

, then it’ll die with the rest if I understood it correctly

My question was how I can make stuff from onStart not die with the rest, but get cancelled in onStop?

Oh, you want something specific to each lifecycle ‘level’? Then you’ll have to do it yourself

And how could I do that by myself?

You could define multiple scopes with nested jobs I suppose, but I’m not fluent enough in coroutines

Sure I am

I usually make things nullable and use calls like

view?.something

so that it’s automagic

Nah, that hides bugs

I agree that it’s not perfect but I don’t have the time for the complex task you’re talking about. But I guess you could implement all that in subclasses of

Activity

and

Fragment

and then use that

I want my code to be correct and not be constantly checking for conditions I didn't write the code to run in

I’m still getting lost between scopes, jobs, context, dispatchers from time to time so I don’t feel I’m ready to implement such thing properly. It would take some time and not be guaranteed to work any better. Once I understand everything more I guess I’ll do something like that. Or once everything explodes 😛

Job is just an interface. I can just create a base class and keep a map of <LifecycleEvent, Job> and just return the correct job depending on the lifecycle.

Hmmm maybe yeah

I.e. I clear my views in onDestroyView, so I don't want a coroutine I started in onCreateView access null views after onDestroyView

@Paul Woitaschek A Fragment is a Lifecycle owner and its lifecycle is per default tied to the Fragment itself. This my cause problems as you described above. Instead of this:

viewModel.liveData.observe(this, Observer { ... } )
}

Do this

viewModel.liveData.observe(viewLifecycleOwner, Observer { ... } )
}

where

this

is replaced by

this.viewLifecycleOwner

This makes sure the LiveData observer will not get callbacks on dead Fragments and only when Views have been created properly, ie between onViewCreated and onViewDestroyed.

I don't use LiveData

You then could tie the

viewLifecycleOwner

to your own life-cycle observers, which could guard against encountering null values for your views in your Fragments.

I'm not talking about any observers, I'm talking about CoroutineScope

You could tie your CoroutineScope to this lifecycle-owner, making your CoroutineScope a life-cycle observer.

I was looking for some kind of "activity observer" the other day to help solve problems like this

@Dico Could this help you: https://developer.android.com/reference/android/app/Application.ActivityLifecycleCallbacks

oh Awesome!

You could create multiple

coroutineScope

properties (not implement them) that gets cancelled on different lifecycle event, then every

.launch

will use correct version of

coroutineScope

. But don’t rely on

job.cancel()

, it will cancel parent job and children, but your “computation” code will still continue to run (null view access might be done after cancelled). So

parentJob.isActive

check should be done. @Paul Woitaschek

If you use

LiveData

in your ViewModel, your Activity's or Fragment's observers should never get notified when View references are null. It's true, Jobs are cancelled only at suspension points, not just anywhere in the code. Either rely on those points or query the

isActive

property and bail out.