App crashes when combining Flow with a MutableStateFlow Code

Question

App crashes when combining Flow with a MutableStateFlow Code in thread

ms · Answer

```val appsFlow Flow lt List lt App gt gt get = appDrawerRepo allAppsFlow combine hiddenAppsRepo onlyHiddenAppsFlow allApps hiddenApps gt allApps minus hiddenApps combine searchFlow filteredApps query gt when query isNotEmpty gt filteredApps filter it name startsWith query ignoreCase = true else gt filteredApps ```

ms · Answer

```private val searchAppFlow = MutableStateFlow ```

ms · Answer

It works if I remove the second combine or use `listOf asFlow `

ms · Answer

java lang NullPointerException Attempt to invoke interface method java lang Object kotlinx coroutines flow Flow collect kotlinx coroutines flow FlowCollector kotlin coroutines Continuation on a null object reference at kotlinx coroutines flow internal CombineKt$combineInternal$2$1 invokeSuspend Combine kt 145 at kotlin coroutines jvm internal BaseContinuationImpl resumeWith ContinuationImpl kt 33 at kotlinx coroutines DispatchedTask run DispatchedTask kt 106 at kotlinx coroutines EventLoop processUnconfinedEvent EventLoop common kt 69 at kotlinx coroutines DispatchedTaskKt resumeUnconfined DispatchedTask kt 244 at kotlinx coroutines DispatchedTaskKt dispatch DispatchedTask kt 161 at kotlinx coroutines CancellableContinuationImpl dispatchResume CancellableContinuationImpl kt 369 at kotlinx coroutines CancellableContinuationImpl resumeImpl CancellableContinuationImpl kt 403 at kotlinx coroutines CancellableContinuationImpl resumeImpl$default CancellableContinuationImpl kt 395 at kotlinx coroutines CancellableContinuationImpl resumeWith CancellableContinuationImpl kt 300

natario1 · Answer

Maybe you are declaring the searchFlow after appsFlow in your file

ephemient · Answer

or in a subclass

ms · Answer

They both are in same class one after other

Abhishek Dewan · Answer

Based on the error appDrawerRepo allAppsFlow seems to be null are you able to collect that flow in isolation and not using combine

ms · Answer

Yes I m unable to use it with combine But instead of `searchFlow` if I give `listOf asFlow ` to combine it works

ms · Answer

Even if I use the combine in reverse order it crashes at the first combine call

louiscad · Answer

Which kotlinx coroutines version are you using

ephemient · Answer

I think an initialization problem is more likely you can try to insert a ` also println searchFlow ` before the ` combine searchFlow `

ms · Answer

This is happening for every `MutableStateFlow` even though I initialized it I m using Jetpack Compose 1 0 0 beta06

louiscad · Answer

< ms> I asked a question

ms · Answer

< louiscad> I m using Jetpack Compose no explicit import

louiscad · Answer

Are you able to reproduce the issue in a simple JVM program

ms · Answer

< louiscad> It worked when I tried it in Kotlin Playground Maybe it s something from Compose side I guess