I have confuse when using lifecycleScope in fragme...

# android

[touge]

I have confuse when using lifecycleScope in fragment, why the fragment’s context is null inside lifecycleScope?
I also asked this on stackoverflow, here is the link: https://stackoverflow.com/questions/56415530/why-the-fragments-context-null-inside-lifecyclescope

[gildor]

It’s make sense. lifecycleScope has lifecycle of fragment and it’s != to lifecycle of context or view

[gildor]

Answered on SO

[touge]

Thanks, really helped!

[gildor]

Thanks, really help but seems I can’t upvote this with enough scorev

You can acceprt answer instead of upvote 😁

[touge]

First time ask question on stackoverflow and founded the accept button😂

[touge]

And I also have a doubt in your answer, the lifecycleScope of Fragment starts from onCreate until onDestroy, are as I know these lifecycle’ events inside onAttach to onDetach?
If in, when using lifecycleScope of Fragment it self may cause a update UI exceptions but not a IllegalStateException of empty context.

[gildor]

may cause a update UI exceptions but not a IllegalStateException of empty context

No, because this job may executing even when context is null

[gildor]

and context is null when fragment is detached

[touge]

I mean that because the onDestroy event happen before onDetach, so the code inside lifecycleScope will be canceled before onDetach

[gildor]

So yes, onCreate initially called after onAttach initially, but context is not avavilable after onDetach and before next onAttach

[gildor]

I see what you mean

[touge]

So why there is a IllegalStateException of empty context when I use the Fragment’s lifecycleScope…

[gildor]

huh

[gildor]

okay, so essentially fragment have context only after super.onCreateView, not directly related to onAttach/onDetach, I updated answer

[Eric Martori]

with the new android support for coroutines in fragment you have viewLifecycleOwner.lifecycleScope which should follow the lifecycle of the view instead o the fragment and prevent this issues

[gildor]

yes, I already mentioned this on SO

[gildor]

I’m digging to source code of Fragment and Fragment manager and understand that I understand less and less 🙈

[touge]

I try to use viewLifecycleOwner.lifecycleScope, but it throw a Exception before onCreateView() or after onDestroyView(), for protected the method be called in a safe way, how about the below way?

fun foo() = viewLifecycleOwnerLiveData.value?.lifecycleScope?.launch {
}

[gildor]

Sure, it throws exception, and this is the whole point, do not start it out of view lifecycle

[Eric Martori]

you can use:
viewLifecycleOwner.lifecycleScope.launchWhenCreated { }
that way inside the coroutine you know that view state is atleast created