StateFlow - Demo

What is StateFlow?

• It is a flow which emits updates to its collectors.
• Value can be observed by collecting values from the flow.

Implementation

ViewModel.kt:

class MainViewModel : ViewModel() {
    private val _countState = MutableStateFlow(0)

    val countState: StateFlow<Int> = _countState

    fun incrementCount() {
        _countState.value++
    }

    fun decrementCount() {
        _countState.value--
    }
}

MainActivity.kt:

class MainActivity : AppCompatActivity() {

    private val viewModel by lazy {
        ViewModelProvider(this)[MainViewModel::class.java]
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        initCountObserver()
        initView()
    }

    private fun initCountObserver() {
        lifecycleScope.launch {
            viewModel.countState.collect { value ->
                textview_count.text = "$value"
            }
        }
    }

    private fun initView() {
        button_plus.setOnClickListener(::incrementCounter)
        button_minus.setOnClickListener(::decrementCounter)
    }

    private fun incrementCounter(view: View) {
        viewModel.incrementCount()
    }

    private fun decrementCounter(view: View) {
        viewModel.decrementCount()
    }
}

Reference

• StateFlow