Hi everyone, I’m trying to find the best way to co...

# flow

[Bernardo Macêdo]

Hi everyone,
I’m trying to find the best way to convert a LiveData that represents a UI state into a StateFlow.

My initial live data code looked like this:

private val _state = MediatorLiveData<State>().apply {
    addSource(livedata2) { value2 -> value?.let { it.copy(someVariable = value2) } }
    value = State(someVariable = "initial value", someOtherVariable = "another initial value")
}
val state: LiveData<State> = _state

The idea is that I have an initial value and also part of the state gets updated whenever a new value is triggered on livedata2

To reach the same behavior using flows, I modified livedata2 to be a SharedFlow (I’ll call it flow2 ) and my _state became a StateFlow.
However I have to collect the flow2 instead of just applying an operator.

private val _state = MutableStateFlow(
        State(
            someVariable = "initial value",
            someOtherVariable = "another intial value"
        )
    ).apply {
        viewModelScope.launch {
            flow2.collect { value2 -> emit(value.copy(someVariable = value2)) }
        }
    }

val state: StateFlow<State> = _state

While it does work, I feel like this is probably not the way to go? Maybe there’s an operator for that. (I tried to use _state.combine(flow2) but my state was not being updated for new events on flow2)

I there a better way to achieve the same result?

[miqbaldc]

google officially release a safer ways to collect the flow: https://medium.com/androiddevelopers/a-safer-way-to-collect-flows-from-android-uis-23080b1f8bda

[Bernardo Macêdo]

Thanks @miqbaldc I’ve read the article, but it is giving guidance on how to collect the flows on the view layer safely (considering the fragment/activity lifecycle). But in this case, I’m trying to merge together 2 sources of information on the viewModel layer. The resulting stateFlow will actually be collected automatically using data binding in my implementation.

I still wonder if there is an operator that allows me to replace the .addSource usage effectively without the need to collect the intermediate flow (flow2 in this case)

[miqbaldc]

Ah I see, looks like we need to wait for either Google add an API extensions as alternative of addSource when using Flow :(