How can I transform a `Flow` that sends three states `Starti

Question

How can I transform a `Flow` that sends three states `Starting` `Progress` and `Finished` from a `sealed class` into a `Flow` that assures receiving `Starting` and `Finished` but conflates `Progress` for backpressure on latency of the collector

diesieben07 · Answer

```sealed class State object Starting State data class Progress val progress Int State object Finished State fun Flow lt State gt checkAndConflate Flow lt State Progress gt return flow lt State Progress gt var first = true var done = false collect check done when first gt check it is State Starting first = false it is State Progress gt emit it else gt check it is State Finished done = true conflate ```

dave08 · Answer

Thanks But I really need it to be `Flow lt State gt ` as a result only with the `Progress` being conflated there s some properties I need on `Started` and `Finished`

diesieben07 · Answer

well should be easy to adapt my code to just re emit those items as well

diesieben07 · Answer

Ah actually not really give me one second

diesieben07 · Answer

```fun Flow lt State gt checkAndConflate Flow lt State gt val conflatedProgressFlow = flow lt State gt var first = true var done = false collect check done when first gt check it is State Starting first = false it is State Progress gt emit it else gt check it is State Finished done = true conflate val startFlow = take 1 val finishedFlow = dropWhile it is State Finished return conflatedProgressFlow onStart emitAll startFlow onCompletion emitAll finishedFlow ``` Not sure if it s the optimal way to do this though

diesieben07 · Answer

Probably not

diesieben07 · Answer

Scratch that definitely not optimal because it runs the flow three times

dave08 · Answer

Yup this problem is a result of Android s Notifications not being designed to receive too many updates I really have to use `delay` in the receiver to skip some of the progress but I need the first and last emissions to display start and finish notification states

dave08 · Answer

So far I had to use broadcastIn and filter on multiple subscribers launched on different coroutines to get this to work not too much cleaner than your solution see no evil

dave08 · Answer

Thanks for the attempt though wink

diesieben07 · Answer

I have another solution one second wink

Dominaezzz · Answer

Would this operator help <https kotlin github io kotlinx coroutines kotlinx coroutines core kotlinx coroutines flow debounce html>

dave08 · Answer

Only for the progress emissions but the first and last ones shouldn t be debounced

dave08 · Answer

`emit 1 ` was skipped over there and `emit 5 ` would have been skipped if it would have some smaller delay

diesieben07 · Answer

```fun Flow lt State gt checkAndConflate Flow lt State gt return channelFlow lt State gt val progressChannel = Channel lt State gt Channel CONFLATED launch try collect if it is State Progress progressChannel send it else this channelFlow send it finally progressChannel close this channelFlow close progressChannel consumeEach this channelFlow send it awaitClose buffer Channel RENDEZVOUS ``` This is what I came up with but it breaks the sequence of elements

diesieben07 · Answer

Revised again and it works now ```fun Flow lt State gt checkAndConflate Flow lt State gt return flow lt State gt coroutineScope val start = CompletableDeferred lt State Starting gt val finish = CompletableDeferred lt State Finished gt val progressChannel = produce lt State Progress gt capacity = Channel CONFLATED collect when it is State Starting gt start complete it is State Progress gt send it is State Finished gt finish complete it emit start await progressChannel consumeEach emit it emit finish await ```

dave08 · Answer

That s not bad ok hand skin tone 3 so to debounce the progress I would just add ``` is State Progress gt delay timoutMillis send it ```

dave08 · Answer

Thanks

Dominaezzz · Answer

I guess a `debounceWhen timeoutMillis ` operator would be nice