Collect from several stateflows

Issue

I have 2 stateFlow's in my viewModel. To collect them in fragment I have to launch coroutines 2 times as below:

    lifecycleScope.launchWhenStarted {
        stocksVM.quotes.collect {
            if (it is Resource.Success) {
                it.data?.let { list ->
                    quoteAdapter.submitData(list)
                }
            }
        }
    }

    lifecycleScope.launchWhenStarted {
        stocksVM.stockUpdate.collect {
            log(it.data?.data.toString())
        }
    }

If I have more stateFlow's, I have to launch coroutines respectively. Is there a better way to handle multiple stateFlow's in my Fragment/Activity or wherever?

Solution

You will need different coroutines, since collect() is a suspending function that suspends until your Flow terminates.

For collecting multiple flows the currently recommended way is:

lifecycleScope.launch {
    lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
        launch {
          stocksVM.quotes.collect { ... }   
        }
    
        launch {
            stocksVM.stockUpdate.collect { ... }
        }
    }
}

Note that the problem with launchWhenStarted is that while your newly emitted items will not be processed your producer will still run in the background.

I'd definitely give this a read, as it explains the current best-practices really well: https://medium.com/androiddevelopers/a-safer-way-to-collect-flows-from-android-uis-23080b1f8bda

Answered By - Róbert Nagy