Android Compose Side Effects Cheatsheet

Android Compose Side Effects Cheatsheet

Concept Summary

• Side effects are operations observable outside a composable function (network calls, listeners, analytics)
• Composables can recompose at any time — side effects in the body run unpredictably
• Compose provides 8 Effect APIs to run side effects in a controlled, lifecycle-aware way
• Each API has different guarantees about when it runs, whether it restarts, and how it cleans up
• Core rule: tie side effects to the composition lifecycle, not to function execution

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Diagram

flowchart TD
    A["Need a side effect?"] --> B{"Needs coroutine?"}
    B -- Yes --> C{"Composition or user event?"}
    C -- Composition --> D["LaunchedEffect"]
    C -- User event --> E["rememberCoroutineScope"]
    B -- No --> F{"Needs cleanup?"}
    F -- Yes --> G["DisposableEffect"]
    F -- No --> H{"Every recomposition?"}
    H -- Yes --> I["SideEffect"]
    H -- No --> J{"Derive state<br/>or convert to Flow?"}
    J -- "Derive state" --> K["derivedStateOf"]
    J -- "Convert to Flow" --> L["snapshotFlow"]
    J -- "Capture latest value" --> M["rememberUpdatedState"]

    style D fill:#059669,color:#fff
    style E fill:#059669,color:#fff
    style G fill:#059669,color:#fff
    style I fill:#059669,color:#fff
    style K fill:#059669,color:#fff
    style L fill:#059669,color:#fff
    style M fill:#059669,color:#fff

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Key APIs

API	Coroutine?	Runs when	Cleanup	Restarts on key?
LaunchedEffect(key)	✅	Enters composition	Coroutine cancelled	✅
rememberCoroutineScope	✅	Manual from callback	Cancelled on leave	N/A
rememberUpdatedState	❌	Every recomposition	❌	N/A
DisposableEffect(key)	❌	Enters composition	onDispose block	✅
SideEffect	❌	Every recomposition	❌	N/A
produceState(init, key)	✅	Enters composition	Coroutine cancelled	✅
derivedStateOf	❌	Source state changes	❌	N/A
snapshotFlow	❌ (produces Flow)	Collected in coroutine	❌	N/A

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Interview Questions

Q1: Why can’t you run side effects directly in a composable body?

Composables can recompose at any time, be skipped, or run in parallel. Direct side effects execute unpredictably — use Effect APIs for lifecycle-aware guarantees.

Q2: LaunchedEffect vs rememberCoroutineScope?

LaunchedEffect auto-launches on composition and restarts on key change. rememberCoroutineScope provides a scope for manual launch from event handlers (clicks, gestures).

Q3: What does rememberUpdatedState solve?

The stale closure problem. It holds the latest value of a changing parameter inside a long-lived effect without restarting the effect.

Q4: When should you use derivedStateOf?

When source state changes more frequently than the derived result (e.g., scroll position changes every pixel but you only care if index > 0). Don’t use it to combine states that change at the same rate.

Q5: What is snapshotFlow?

Converts Compose State into a cold Flow with built-in distinctUntilChanged. Use it when you need Flow operators (debounce, filter, map) on Compose state.

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Common Pitfalls

⚠️ Suspend calls directly in composable body — use LaunchedEffect instead.

⚠️ Passing Unit as key when effect depends on a parameter — the effect never restarts; pass the actual dependency as the key.

⚠️ Using SideEffect for one-time operations — it runs on every recomposition; use LaunchedEffect(Unit) for one-shot work.

⚠️ Empty onDispose {} when cleanup is actually needed — causes resource leaks (listeners, observers).

⚠️ Overusing derivedStateOf — don’t use it to combine states that change at the same rate (e.g., "$firstName $lastName"). It only helps when the source changes more often than the derived result.

⚠️ Collecting snapshotFlow outside a coroutine — it produces a cold Flow that must be collected inside a LaunchedEffect or similar coroutine scope.

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Quick Reference Table

Scenario	API	Key
Fetch data on screen open	LaunchedEffect(id)	Data identifier
One-time initialization	LaunchedEffect(Unit)	Unit
Button click coroutine	rememberCoroutineScope	N/A
Register lifecycle observer	DisposableEffect(owner)	Lifecycle owner
Sync state to analytics	SideEffect	N/A
Convert Flow to State	collectAsStateWithLifecycle()	N/A
Avoid stale callback	rememberUpdatedState	N/A
Convert suspend to State	produceState(init, key)	Data identifier
Show button after scroll threshold	derivedStateOf { index > 0 }	N/A
Debounce search from Compose state	snapshotFlow { query }	N/A
Analytics on scroll event	snapshotFlow + filter	N/A