StateFlow vs SharedFlow in Android: Complete Guide with Real Use

In modern Android development, managing UI state and one-time events correctly is critical for building scalable, bug-free applications. With Kotlin Coroutines, developers now rely heavily on Flow, especially StateFlow and SharedFlow.

However, confusion between StateFlow vs SharedFlow is one of the most common causes of:

• Duplicate navigation
• Snackbar re-triggering on rotation
• Inconsistent UI behavior
• Fragile ViewModels

This article provides a clear, practical, production-ready explanation of StateFlow vs SharedFlow in Android, including real use cases, best practices, and anti-patterns.

Why StateFlow vs SharedFlow Matters in Android

Android UI is driven by two fundamentally different concepts:

1. UI State – what the screen should display
2. UI Events – actions that should happen once

Trying to represent both using a single mechanism leads to architectural instability.

This is exactly why StateFlow and SharedFlow exist as separate tools.

What Is StateFlow in Android?

StateFlow is a hot Flow designed to hold and expose UI state.

Key characteristics of StateFlow

• Always has an initial value
• Always holds the latest state
• Replays the latest value to new collectors
• Perfect for UI rendering
• Configuration-change safe

Typical StateFlow use cases

• Screen UI state
• Loading / success / error states
• Form input values
• ViewModel state containers

Example: StateFlow in a ViewModel

data class LoginUiState(
    val isLoading: Boolean = false,
    val error: String? = null
)

private val _uiState = MutableStateFlow(LoginUiState())
val uiState = _uiState.asStateFlow()

If the Activity or Fragment is recreated, the UI immediately renders correctly.

This is the defining feature of StateFlow.

What Is SharedFlow in Android?

SharedFlow is a hot Flow for events, not state.

Key characteristics of SharedFlow

• No required initial value
• Emits values independently of collectors
• Can be configured for replay and buffering
• Designed for one-time events

Typical SharedFlow use cases

• Navigation events
• Snackbars and Toasts
• Dialog triggers
• One-time error messages
• Analytics events

Example: SharedFlow for UI events

private val _events = MutableSharedFlow<UiEvent>(
    replay = 0,
    extraBufferCapacity = 1
)
val events = _events.asSharedFlow()

If the UI is not collecting at the moment of emission, the event is intentionally lost.
This behavior is correct and desirable for one-time actions.

StateFlow vs SharedFlow: Side-by-Side Comparison

The Golden Rule

If the UI needs the value to draw itself → use StateFlow
If the UI needs to react once → use SharedFlow

This rule alone eliminates most Android UI bugs related to Flow.

Using StateFlow and SharedFlow Together (Best Practice)

In real Android applications, you almost always use both.

Production-ready ViewModel example

class LoginViewModel : ViewModel() {

    private val _uiState = MutableStateFlow(LoginUiState())
    val uiState = _uiState.asStateFlow()

    private val _events = MutableSharedFlow<UiEvent>()
    val events = _events.asSharedFlow()

    fun login() {
        _uiState.value = _uiState.value.copy(isLoading = true)

        viewModelScope.launch {
            // business logic
            _events.emit(UiEvent.NavigateToHome)
        }
    }
}

• StateFlow → UI rendering
• SharedFlow → UI effects
• Clean separation
• Predictable behavior
• Easy testing

Common Mistakes to Avoid

Using SharedFlow for UI state

Leads to missed values and broken UI rendering.

Using StateFlow for navigation

Causes navigation to trigger again on rotation.

Setting replay > 0 for events

Re-introduces the exact bugs SharedFlow was created to fix.

Mixing state and events in one Flow

Destroys clarity and testability.

SharedFlow vs LiveData vs SingleLiveEvent

• LiveData → legacy, lifecycle-bound
• SingleLiveEvent → workaround with known issues
• SharedFlow → coroutine-native, explicit, testable

In modern Android development, SharedFlow is the correct replacement for SingleLiveEvent.

Final Thoughts: Which One Should You Use?

• Use StateFlow for UI state
• Use SharedFlow for one-time events
• Never mix responsibilities
• Design ViewModels with clear intent

This separation scales cleanly across:

• MVVM
• MVI
• Jetpack Compose
• Multi-module architectures

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