I have a `Flow lt Product gt ` which emits one by one how I

Question

I have a `Flow lt Product gt ` which emits one by one how I make it to collect those in list so I could receive a list in `collect `

louiscad · Answer

You can create a custom operator that creates an empty mutable list before collecting the source flow and emits the list after each collected element added You can also use `scan`

Mohamed Ibrahim · Answer

what do you think of this ```fun lt T gt Flow lt T gt intoList Flow lt List lt T gt gt return flow val bag = arrayListOf lt T gt collect bag add it emit bag ```

streetsofboston · Answer

Note that works only if the source Flow ends completes Otherwise nothing will be ever emitted

Mohamed Ibrahim · Answer

why

streetsofboston · Answer

If the source Flow does not end your call to `collect` will suspend forever It will keep adding items to `bag` but `emit bag ` will never be called in that case

streetsofboston · Answer

Your source Flow starts as soon as your code calls `collect` on it and your `collect` call suspends The lambda provided to your `collect` call will be called each time your source producer Flow calls `emit` In the mean time your call to `collect` remains suspended Your call to `collect` resumes when the lambda provided to your source producer Flow returns ends

louiscad · Answer

< Mohamed Ibrahim> You need to call `emit` after each call to `add` inside the `collect` lambda

streetsofboston · Answer

That would be like a `scan` operator emitting a growing list each time I think he was more thinking about a final terminating and suspending `toList ` method on the source Flow but I could be wrong

louiscad · Answer

That one already exists < streetsofboston>

streetsofboston · Answer

I wasn t sure it already existed grinning But it seems the original poster has some issue with how Flows and their collection exactly works

Mohamed Ibrahim · Answer

The issue with me that if I used toList I have to use try catch and may I still have RxJava concepts in mind And not breaking the stream was my purpose

Mohamed Ibrahim · Answer

I don t know if that even correct for Flow

Mohamed Ibrahim · Answer

The scan operator is very handy here is an example of it ```val toList = flowOf 1 2 3 scan emptyList lt Int gt acc value gt acc + value toList ```

streetsofboston · Answer

Yup if you are looking on how that list grows for each emission using `scan` is a great way to do so But if you just need get one final list of all emissions without any intermediate ones `toList ` is your friend but that requires the flow to end since a list can only contain a finite amount of items