how to avoid repeatOnLifecycle excute again and again when fragment resume

Question

how can I avoid the collect{} code execute again when navigate back to the fragment.

ViewModel class

    private val _commitResult = MutableStateFlow<Map<String, Any>>(mapOf())
    val commitResult: StateFlow<Map<String, Any>> = _commitResult
Fragment code like this:

    viewLifecycleOwner.lifecycleScope.launch {
            viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED){
                viewModel.commitResult.collect { data ->
                    Logger.i("commitResult $data")
                    //navigate to another fragment
                }
            }
        }

when I change the _commitResult value in viewModel first, jump to another fragment works fine. unfortunately, when I go back to the fragment. collect{ // navigate to another fragment} will excute again.

I know when back to the fragment. onCreateView excute again and viewModel will emit the data store before, so thecollect { // navigate to another fragment} excute. How can I avoid this?

same as LiveData, I use Event to fix this with LiveData.

open class Event<out T>(private val content: T) {

var hasBeenHandled = false
    private set // Allow external read but not write

/**
 * Returns the content and prevents its use again.
 */
fun getContentIfNotHandled(): T? {
    return if (hasBeenHandled) {
        null
    } else {
        hasBeenHandled = true
        content
    }
}

/**
 * Returns the content, even if it's already been handled.
 */
fun peekContent(): T = content
}

how can I handle this with stateflow? actually I don't like Event<.> to handle this, am I use the stateflow in a wrong way? how I can fix this? If anyone who can help, thanks in advance.

It sounds like a typical problem but nobody answered it!!! However, you can achieve the expected result by using SharedFlow with replay = 0. — Yasin Hajilou, Dec 20 '21 at 15:54

score 0 · Answer 1 · answered Apr 29 '22 at 11:13

StateFlow keeps it's state, so I'd suggest either:

A) Use SharedFlow. https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/-shared-flow/

B) Use a pattern where you handle the dismissal of events

class Vm: ViewModel() {
  
  private val mEvent = MutableStateFlow<MyResult?>(null)
  val event = mEvent.asStateFlow()

  fun dismissEvent() {
    mEvent.value = null
  }

}

class Frag: Fragment() {
  override fun onViewCreated() {
     vm.event.collect {
       navigate()
       vm.dismissEvent()
     }
  }
}

how to avoid repeatOnLifecycle excute again and again when fragment resume

1 Answers1