[FIXED] Unsubscribe from Kotlin Flow without cancelling current scope

Issue

I am subscribing to a Kotlin SharedFlow of booleans within a repeatOnLifecycle block in Android. I want to subscribe until I receive the first true boolean and act on it.

As soon as the first true boolean is received I need to unsubscribe and run the processing funtion within the lifecyce scope so it gets cancelled when the lifecycle transitions to an invalid state.

When I call cancel on the current scope and embed the processing code in a NonCancellable context it will not be cancelled on lifecycle events.

I think I would want something like a takeWhile inlcuding the first element that did not match the predicate.

Below are some sample flows where I want to collect all elements until the $ sign:

true $ ...
false, true $ ...
false, false, true $ ...

Sample code:

viewLifecycleOwner.lifecycleScope.launch {
    repeatOnLifecycle(Lifecycle.State.STARTED) {
        flowOfInterest.collectLatest {
            if (it) {
                stopCollection()
                doOnTrue()
            } else {
                doOnFalse()
            }
        }
    }
}

What is the correct/simplest way to achieve this behavior?

Thanks!

Solution

You can use the first function to continue collecting until the given predicate returns true.

viewLifecycleOwner.lifecycleScope.launch {
    repeatOnLifecycle(Lifecycle.State.STARTED) {
        flowOfInterest.first { 
            if(it) doOnTrue() else doOnFalse()
            it 
        }
    }
}

Answered By - Arpit Shukla
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)