Hello, World! Is there an easy way to implement `MutableStateFlow`? For instance, does something sim...

# flow

[bod]

Hello, World! Is there an easy way to implement MutableStateFlow? For instance, does something similar to callbackFlow {} exist?

[gildor]

What you trying to achieve?

[bod]

Hi! I'd like to expose some kind of persisted data (Android's SharedPreferences) as MutableStateFlow s

[bod]

I managed to do it by having a wrapped MutableStateFlow but that involves quite a bit of boilerplate

[bezrukov]

You can transform any flow (e.g. callbackFlow) into StateFlow via flow.stateIn

[bod]

oh! Thanks a lot, let me have a look.

[bod]

oh but that creates a non mutable StateFlow though - my need is for a mutable one.

[gildor]

yep, you cannot return data back using stateIn

[gildor]

I think the easiest solution is just create a standard MutableStateFlow() and allow update it from two sides

[gildor]

You can do something like this:

class FlowPreferences {
    private val flows = HashMap<String, MutableStateFlow<Any>>()
    private val sharedPreferences = TODO()
    private val someScope: CoroutineScope = TODO("Lifecycle of this scope really depends on your case, it can be just GlobalScope, if preferences are global")
    fun stringFlow(key: String): MutableStateFlow<String> {
        flows.getOrPut(key) {
            MutableStateFlow<String>(sharedPreferences.getString(key)).apply {
                someScope.launch {
                    collect {
                        if (sharedPreferences != it) {
                            sharedPreferences.edit().putString(it).apply()
                        }
                    }
                }
                //TODO: it also possible observe sharedPreferences and update flow
            }
        }
    }
}

[gildor]

Though, I’m not sure that having hot flows for this case is right solution, I would just replace this with non-mutable StateFlow and additional method for update, yes, a bit more code, but easier to maintain and clear separation of observable state from updating of this state (they also could be parts of separate interfaces)

[bod]

Thanks a lot, interesting approach!

[bod]

you can see here how I did it (the wrapping approach), to compare: https://github.com/BoD/android-kprefs/blob/mutable-state-flow/library/src/main/kotlin/org/jraf/android/kprefs/PreferenceFlowProperty.kt#L68

[Raul]

really interesting! Benoit