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#coroutines
Title
# coroutines
d

Dean Djermanović

07/24/2021, 8:45 AM
I have following layers in my app:
UI
,
Presentation
,
Business
and
Data
. I’m launching a coroutines from the
Presentation
layer where I have setup
backgroundScope
with an exception handler. I want to share a
Flow
in the data layer using
shareIn
operator. Which scope should I pass to it? If I pass different scope than the
backgroundScope
used in the presentation layer, the exceptions won’t be propagated up to the exception handler in that
backgroundScope
. Also I want to share that
Flow
globally, not in the scope of that
ViewModel
in the presentation layer. So the question is how to share a
Flow
on the data layer from some repository class which is a singleton and still propagate the exceptions to the exception handler that’s setup in the presentation layer?
n

Nick Allen

07/25/2021, 6:42 PM
Do you really need the Data layer
Flow
to be a singleton? This becomes trivial if you just share within the Presentation layer. If you want
backgroundScope
to handle the exception, you have to throw it in the Presentation layer. If the Data layer encounters an error, it can encode that as an error event in the
Flow
(part of a sealed class or
Result
). The Presentation layer can re-throw the exception when it encounters the error event. This pattern of encoding errors into the data is what the
SharedFlow
docs mean when they say "All errors and completion signals should be explicitly materialized if needed" Don't forget about situations if an error may happen when there is no Presentation layer (do you need to save it?), or if many collectors may encounter the same Data layer exception (will you spam the user or crash reporting?).