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.

Kotlin StateFlow

Implementation

Libraries

References