StateFlow

A hot flow that holds a single value and emits updates to collectors. Always has an initial value.

Basic Usage

class MyViewModel : ViewModel() {
    private val _uiState = MutableStateFlow("Initial")
    val uiState: StateFlow<String> = _uiState.asStateFlow()

    fun updateState(newValue: String) {
        _uiState.value = newValue
    }
}

Collect StateFlow in Composable

@Composable
fun MyScreen(viewModel: MyViewModel = viewModel()) {
    val uiState by viewModel.uiState.collectAsState()

    Text(text = uiState)
}

StateFlow vs LiveData

StateFlow	LiveData
Requires initial value	Can be null initially
Kotlin coroutines based	Lifecycle-aware by default
collectAsState() in Compose	observeAsState() in Compose

StateFlow vs SharedFlow

StateFlow	SharedFlow
Always has current value	No initial value required
.value to read current	No .value property
Conflates (skips intermediate)	Configurable buffer/replay
Best for UI state	Best for events/actions

Using by keyword

To use the by keyword in compose, import:

import androidx.compose.runtime.getValue
import androidx.compose.runtime.setValue

Manual Recompose

var count by remember { mutableStateOf(0) }
key(count){
    // recompose when the var count change
}

snapshotFlow

Kind of like LaunchedEffect but allows use in non-composable functions

snapshotFlow { searchQuery }
    .filter { it.length > 2 } // Only emit if query is longer than 2 characters
    .debounce(500) // Wait 500ms after last change
    .collect { query ->
        println("Search query: $query")
        // Example: Trigger a network search
    }