Kotlin StateFlow & SharedFlow

Kotlin StateFlow & SharedFlow – Complete Beginner Guide

Modern Android and Kotlin applications require efficient ways to manage state and events in asynchronous programming. If you are using Kotlin Coroutines, you have probably heard about StateFlow and SharedFlow.

These two APIs are part of Kotlin’s Flow library and are widely used in:

• Android ViewModel

• MVVM architecture

• Reactive UI updates

• Event handling

• Real-time data streams

In this SEO-optimized, beginner-friendly guide, you will learn:

• What StateFlow is

• What SharedFlow is

• Differences between them

• How they work with coroutines

• Real-world Android examples

• Best practices

• Common beginner mistakes

Let’s get started

What Is Flow in Kotlin?

Before understanding StateFlow and SharedFlow, you must know about Flow.

Flow is a stream of data that emits values asynchronously over time.

Example:

Flow is cold by default, meaning it only runs when collected.

What Is StateFlow in Kotlin?

StateFlow is a special type of Flow that:

• Holds a single state value

• Always has a current value

• Emits updates when value changes

• Is hot (always active)

Think of StateFlow as a state holder observable.

Key Features of StateFlow

•  Always has initial value
•  Stores latest state
•  Emits only when value changes
•  Works perfectly with ViewModel
•  Ideal for UI state

Creating StateFlow

Here:

• _count is mutable

• count is exposed as read-only

Collecting StateFlow

Whenever value changes, UI updates.

What Is SharedFlow in Kotlin?

SharedFlow is another hot flow that:

• Emits values to multiple collectors

• Does NOT require initial value

• Does NOT hold state by default

• Used for events

Think of SharedFlow as a broadcast system.

Key Features of SharedFlow

•  No initial value required
•  Can emit events
• Multiple subscribers supported
•  Configurable replay behavior
• Suitable for one-time events

Creating SharedFlow

Collecting SharedFlow

SharedFlow sends events to all active collectors.

StateFlow vs SharedFlow – Key Differences

When Should You Use StateFlow?

Use StateFlow when:

• Managing UI state

• Holding latest data

• Observing ViewModel data

• Handling configuration changes

Example:

• Loading state

• User profile data

• Counter value

When Should You Use SharedFlow?

Use SharedFlow when:

• Emitting one-time events

• Showing Toast messages

• Navigation events

• Snackbar triggers

Example:

Real-World Android Example – State Management

UI observes state changes.

Real-World Android Example – Event Handling

UI collects and navigates.

Replay in SharedFlow

SharedFlow allows replaying values to new subscribers.

This stores last emitted value.

Hot vs Cold Flow

StateFlow and SharedFlow are hot flows.

Common Beginner Mistakes

 Using StateFlow for One-Time Events

StateFlow replays last value — not ideal for events.

 Forgetting to Launch Coroutine for Emit

SharedFlow emit must run inside coroutine.

 Exposing Mutable Flow

Always expose read-only version.

 Ignoring Lifecycle

Always collect flows in lifecycle-aware scope.

Best Practices

•  Use StateFlow for UI state
•  Use SharedFlow for events
•  Keep MutableFlow private
•  Expose immutable flow publicly
•  Collect inside lifecycleScope or viewModelScope

Performance Considerations

• StateFlow is lightweight

• SharedFlow supports multiple subscribers

• Avoid heavy work inside collectors

• Use distinctUntilChanged for optimization

Frequently Asked Questions (FAQs)

1. What is StateFlow in Kotlin?

StateFlow is a hot flow that holds and emits the latest state value.

2. What is SharedFlow in Kotlin?

SharedFlow is a hot flow used for broadcasting events to multiple collectors.

3. What is the difference between StateFlow and SharedFlow?

StateFlow stores state with initial value. SharedFlow is used for events and does not require initial value.

4. Are StateFlow and SharedFlow cold or hot?

Both are hot flows.

5. When should I use StateFlow?

Use it for managing UI state in ViewModel.

Conclusion

StateFlow and SharedFlow are powerful tools in modern Kotlin and Android development.

You learned:

• What StateFlow is

• What SharedFlow is

• Key differences

• Real-world usage

• Best practices

• Common mistakes

Mastering these APIs will improve your reactive programming skills in Kotlin.