compose-animations

Compose: animations

Core principle

Pick the smallest API that matches the problem: built-in visibility and layout transitions first, then a single animated value, then a shared transition object when several values must move together, then gesture-level or imperative APIs when the framework cannot express the motion.

Review procedure

1. Identify the visual job: show/hide, one value, coordinated values, content swap, size change, or gesture-driven motion.
2. Choose the smallest API from the table below.
3. Check lifecycle semantics: should hidden content leave composition, keep focus/state, or only become transparent?
4. Check identity: render each AnimatedContent branch from its content-lambda target, then choose contentKey by visual shape rather than payload churn.
5. Check performance: keep frame-rate animation values as State and read them in layout/draw block modifiers when possible.
6. Escalate to Animatable or lower-level APIs only when target-state animation cannot express the motion.
7. Finish when the chosen API matches the visual and lifecycle needs, any content-swap identity is preserved, no simpler API fits, and the relevant behavior has been verified.

Pick the smallest animation API

Appear and disappear

Prefer AnimatedVisibility when the UI should leave or join the tree with enter/exit transitions.

AnimatedVisibility(visible = expanded) {
    Text("Details…")
}

animateFloatAsState on alpha only fades; the composable stays in composition and continues to participate in layout unless you gate it yourself. Use that tradeoff when you intentionally keep children mounted (state, focus) but visually hidden. For true remove-from-tree behavior, use AnimatedVisibility (or conditional composition with AnimatedVisibility / AnimatedContent patterns from the quick guide).

Background color

Use animateColorAsState for smooth color targets.

For animated fills behind children, the quick guide recommends drawing with Modifier.drawBehind rather than Modifier.background() so the animated color is applied in the draw phase appropriately for performance.

val background = animateColorAsState(
    targetValue = if (selected) selectedColor else idleColor,
    label = "background",
)
Box(
    Modifier.drawBehind { drawRect(background.value) },
) { /* content */ }

Size changes

Modifier.animateContentSize() animates layout size changes—common for expanding/collapsing text or dynamic chips—without hand-rolling width/height animations.

Value-based animations (animate*AsState)

Compose provides animate*AsState for Float, Dp, Color, Size, Offset, Rect, Int, IntOffset, IntSize, and more. You supply the target; the API owns the animation state.

• Pass an AnimationSpec via animationSpec (e.g. spring, tween) when defaults are wrong for the UI.
• Set a distinct label for debugging and tooling when multiple animations exist in one composable.
• For completion or sequencing details, see Value-based animations.

val width by animateDpAsState(
    targetValue = if (expanded) 200.dp else 56.dp,
    animationSpec = spring(dampingRatio = 0.7f, stiffness = Spring.StiffnessMedium),
    label = "fabWidth",
)

Multiple properties: rememberTransition

When one piece of state (e.g. enum class Phase { A, B, C }) should drive several animated values in lockstep, use rememberTransition and define child animations on that transition:

val transition = rememberTransition(targetState = phase, label = "phase")
val alpha by transition.animateFloat(label = "alpha") { target ->
    if (target == Phase.Visible) 1f else 0f
}
val offset by transition.animateDp(label = "offset") { target ->
    if (target == Phase.Visible) 0.dp else 24.dp
}

Avoid multiple independent animate*AsState calls that should stay visually synchronized but can drift if specs or targets diverge. Older code may use updateTransition; prefer rememberTransition for new code.

Choosing between content-level APIs

Use the official Choose an animation API tree when the table is not enough. Compressed rules:

Art-based motion (illustrations, Lottie, complex vector timelines) is outside this skill; use dedicated libraries.

Decision flow (high level)

flowchart TD
  start[Animation_need]
  start --> showHide{Show_or_hide_subtree}
  showHide -->|yes| av[AnimatedVisibility]
  showHide -->|no| oneProp{Single_property_to_target}
  oneProp -->|yes| asState["animate*AsState"]
  oneProp -->|no| multiProp{Many_props_one_state}
  multiProp -->|yes| rt[rememberTransition]
  multiProp -->|no| swapTree{Different_composable_content}
  swapTree -->|yes| ac[AnimatedContent_or_Crossfade]
  swapTree -->|no| advanced[Animatable_or_lower_level]

AnimatedContent keys for state holders

AnimatedContent can keep outgoing and incoming content composed at the same time. Render from the content lambda's target value, not a captured outer state value; otherwise both branches can show the latest state and effects inside them can act on the wrong content identity.

// Wrong: outgoing and incoming branches both read the latest selectedId.
AnimatedContent(targetState = selectedId) {
    Destination(selectedId)
}

// Right: each branch keeps the identity AnimatedContent assigned to it.
AnimatedContent(targetState = selectedId) { targetId ->
    Destination(targetId)
}

When AnimatedContent receives a state-holder wrapper such as AsyncResult<T>, Result<T>, or a sealed UiState, decide what should actually trigger the transition. Usually the animation should run when the content shape changes (loading → content → error), not when the payload inside the same shape changes.

Use contentKey to map rich state to the animation identity:

AnimatedContent(
    targetState = result,
    contentKey = { state ->
        when (state) {
            AsyncResult.Loading -> "loading"
            is AsyncResult.Success -> "content"
            is AsyncResult.Error -> "error"
        }
    },
    label = "profile-content",
) { state ->
    when (state) {
        AsyncResult.Loading -> Loading()
        is AsyncResult.Success -> Profile(state.value)
        is AsyncResult.Error -> ErrorMessage(state.throwable)
    }
}

Without contentKey, every unequal Success(value) can be treated as new content. That is useful if a payload change should animate, but noisy when fresh data updates the same screen shape.

Choose keys by visual shape:

Animated values and composition performance

animate*AsState returns State that updates frequently. If that value feeds Modifier.offset, Modifier.graphicsLayer, scroll-adjacent layout, or other frame-rate paths, avoid reading it in the composable body with by and then passing it into value-form modifiers—use deferred reads (block modifiers, draw/ layout lambdas) instead. See Compose performance.

If recomposition counters spike during motion unrelated to bad stability, see Compose performance.

Escalation points

Load the official docs when one of these applies:

Common mistakes

RED/GREEN agent scenarios

1. Novel case: focus moves while AnimatedContent swaps between two destinations. RED renders both branches from captured outer state. GREEN renders and keys effects from the lambda target, then tests focus after the transition settles.
2. Counterexample: a single composable only animates one color value. GREEN keeps animateColorAsState and does not introduce AnimatedContent or content identity machinery.

When not to use this skill

• Side-effect timing (LaunchedEffect, clicks launching work): use Compose state and effects.
• Deep performance tuning of where snapshot state is read: use Compose performance as the primary reference.