Kotlin StateFlow

Sample Android application that show how can we use Kotlin Coroutines StateFlow.

Implementation

StateFlow is a new class introduced in version 1.3.6 of the Kotlin Coroutines library which works in the following way:

• It's a Flow with a single updatable data value that emits updates to the value to its collectors.
• Updates to the value can be observed by collecting values from this flow.
• It's useful as a data-model class to represent any kind of state.
• It's designed to completely replace ConflatedBroadcastChannel in the future.

For example, the following class represents an integer state that increments its value by calling the method incrementCount:

class CountModel {
    private val _countState = MutableStateFlow(0) // Private mutable state flow
    val countState: StateFlow<Int> get() = _countState // Public read-only state flow

    fun incrementCount() {
        _countState.value++
    }
}

Now in a possible activity we can observe countState to keep track of its updates:

lifecycleScope.launch {
    countModel.countState.collect { value ->
        countTextView.text = "$value"
    }
}

This collector will be executed whenever the value of countState is updated. Also it's lifecycle-aware as we’ve used it under lifecycleScope.

Libraries

• Kotlin + Coroutines
• Jetpack
  • ViewModel
  • Lifecycle
• Koin
• Timber

References

• StateFlow, End of LiveData?
• StateFlow