Update CoroutineScope docs to recommend explicit scope

[elizarov]

CoroutineScope documentation currently recommends the following code pattern:

class MyActivity : AppCompatActivity(), CoroutineScope by MainScope() {
    ...
}

It's time to update it to explict scope style, which seems to be winning in its clarity and popularity:

class MyActivity : AppCompatActivity() {
    private val scope = MainScope() 
    ...
}

[kpritam]

As per this guideline, can you please help me with the following example if any changes need to be done?

class Script : CoroutineScope {
    private val executor = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
    private val job = Job()

    override val coroutineContext: CoroutineContext get() = job + executor
    
    // ....
}

[qwwdfsad]

@kpritam

class Script : CoroutineScope {
    private val executor = ... // Separate variable to close it later
    private val scriptScope = CoroutineScope(executor)
}

[kpritam]

@kpritam

class Script : CoroutineScope {
    private val executor = ... // Separate variable to close it later
    private val scriptScope = CoroutineScope(executor)
}

Thanks @qwwdfsad , Just to confirm, do you mean like this?

class Script {
    private val executor = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
    private val scriptScope = CoroutineScope(executor)
    init {
        scriptScope.launch { delay(1000) }
    }
}

[guelo]

Not sure if it matters for the documentation, but in my team instead of doing something like this

class Activity {
    private val mainScope = MainScope()
    
    fun destroy() {
        mainScope.cancel()
    }
}

we created a class that ties the lifecycles and scope together using androidx.lifecycle observer.

class LifecycleScope(lifecycleOwner: LifecycleOwner) : CoroutineScope, LifecycleObserver {

    init {
        lifecycleOwner.lifecycle.addObserver(this)
    }

    override val coroutineContext = SupervisorJob() + Dispatchers.Main

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun destroy() = coroutineContext.cancel()
}

Then we don't have to worry about managing the scope cancellation in every activity

class Activity: FragmentActivity() {
    private val scope = LifecycleScope(this)
}

I suspect the android team didn't create something like this because they're trying to guide people to keep all coroutine stuff in their ViewModels and to only use LiveData in Activitys and Fragments. But I find it's sometimes still useful to use coroutines in the Activitys and Fragments.

[zsmb13]

@guelo: this is actually provided in a first-party way, it's called LifecycleScope, and you can access it on any LifecycleOwner (Activity, Fragment, Fragment view owner): https://developer.android.com/topic/libraries/architecture/coroutines#lifecyclescope

[guelo]

Well now I feel stupid. I'm not sure how I missed that.

…

On Tue, Mar 24, 2020 at 11:25 PM Márton Braun ***@***.***> wrote: @guelo <https://github.com/guelo>: this is actually provided in a first-party way, it's called LifecycleScope, and you can access it on any LifecycleOwner (Activity, Fragment, Fragment view owner): https://developer.android.com/topic/libraries/architecture/coroutines#lifecyclescope — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1581 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA4CXC4ZP4AWBZDWYTHEVUDRJGPW5ANCNFSM4I3NHLNQ> .