Android Academy · Lesson

animate*AsState Basics

Smoothly animate single values.

Lesson 2 of 413 steps

animate*AsState Basics is a free Android Academy lesson on CoddyKit. This is lesson 2 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Android Academy learning path, and your progress syncs across the web and the CoddyKit app. The Android Academy course includes 4 lessons in total.

Animate a Single Value

The simplest way to animate in Compose is the animate*AsState family. You give it a target value, and it returns a State that smoothly animates from the current value to the target whenever the target changes.

There's a variant for each common type: animateFloatAsState, animateDpAsState, animateColorAsState, animateOffsetAsState, and more.

animateFloatAsState

animateFloatAsState animates a single Float. A common use is opacity (alpha). When visible flips, the returned alpha glides between 0f and 1f.

Note the by keyword: it lets you read the animated State<Float> directly as a plain Float.

@Composable
fun FadingLabel(visible: Boolean) {
    val alpha by animateFloatAsState(
        targetValue = if (visible) 1f else 0f,
        label = "alpha"
    )
    Text(
        "Hello",
        modifier = Modifier.graphicsLayer { this.alpha = alpha }
    )
}

animateDpAsState

UI sizes and offsets use Dp, so reach for animateDpAsState to animate padding, size, or position.

Here a box grows from 80dp to 160dp when toggled. Because we feed the animated Dp into size(), the box smoothly resizes.

@Composable
fun GrowingBox(big: Boolean) {
    val size by animateDpAsState(
        targetValue = if (big) 160.dp else 80.dp,
        label = "size"
    )
    Box(
        Modifier
            .size(size)
            .background(Color.Blue)
    )
}

animateColorAsState

To animate colors, use animateColorAsState. It interpolates across the color space so transitions look smooth and natural rather than flickering through odd in-between hues.

Here a status dot animates between red and green based on a boolean.

@Composable
fun StatusDot(online: Boolean) {
    val color by animateColorAsState(
        targetValue = if (online) Color(0xFF4CAF50) else Color(0xFFF44336),
        label = "status-color"
    )
    Box(
        Modifier
            .size(16.dp)
            .clip(CircleShape)
            .background(color)
    )
}

Customizing with animationSpec

By default these helpers use a gentle spring. Pass an animationSpec to control timing. Use tween for a fixed duration with an easing curve.

This panel slides over 400ms with a smooth accelerate-then-decelerate curve.

@Composable
fun SlidingPanel(open: Boolean) {
    val offset by animateDpAsState(
        targetValue = if (open) 0.dp else 250.dp,
        animationSpec = tween(
            durationMillis = 400,
            easing = FastOutSlowInEasing
        ),
        label = "offset"
    )
    Box(Modifier.offset(x = offset)) { /* content */ }
}

Easing Curves

Easing shapes how an animation accelerates and decelerates. Compose ships several:

LinearEasing - constant speed (mechanical feel).
FastOutSlowInEasing - the Material default; quick start, soft finish.
LinearOutSlowInEasing - for elements entering the screen.
FastOutLinearInEasing - for elements exiting.

Choosing the right easing makes motion feel intentional rather than robotic.

val progress by animateFloatAsState(
    targetValue = if (done) 1f else 0f,
    animationSpec = tween(500, easing = LinearOutSlowInEasing),
    label = "progress"
)

Spring Specs

Instead of a fixed duration you can use a spring, which feels physical and natural. A spring is defined by dampingRatio (how bouncy) and stiffness (how fast).

Springs are great because they adapt smoothly even when the target changes mid-animation.

val scale by animateFloatAsState(
    targetValue = if (active) 1.2f else 1f,
    animationSpec = spring(
        dampingRatio = Spring.DampingRatioMediumBouncy,
        stiffness = Spring.StiffnessLow
    ),
    label = "scale"
)

Reacting to Finish

Sometimes you need to do something when an animation completes, like firing a callback once a value reaches its target. animate*AsState accepts a finishedListener for exactly this.

val alpha by animateFloatAsState(
    targetValue = if (gone) 0f else 1f,
    label = "alpha",
    finishedListener = { finalValue ->
        if (finalValue == 0f) onFullyHidden()
    }
)

Animate Multiple Properties

You can combine several animate*AsState calls to animate more than one property at once. Each tracks its own value, and together they create a richer effect.

Here a chip both scales and changes color when selected.

@Composable
fun SelectableChip(selected: Boolean, text: String) {
    val scale by animateFloatAsState(if (selected) 1.1f else 1f, label = "s")
    val bg by animateColorAsState(
        if (selected) Color(0xFF3F51B5) else Color.LightGray,
        label = "bg"
    )
    Box(
        Modifier
            .graphicsLayer { scaleX = scale; scaleY = scale }
            .clip(RoundedCornerShape(16.dp))
            .background(bg)
            .padding(horizontal = 12.dp, vertical = 6.dp)
    ) { Text(text) }
}

A Spring in Pure Kotlin

To build intuition for what a spring "does", here's a tiny pure-Kotlin simulation. It nudges a value toward a target each step with some damping, much like Compose's spring resolves toward your target value over many frames.

fun main() {
    var value = 0f
    val target = 100f
    var velocity = 0f
    val stiffness = 0.1f
    val damping = 0.6f
    repeat(6) { step ->
        val force = (target - value) * stiffness
        velocity = (velocity + force) * damping
        value += velocity
        println("step $step -> ${"%.1f".format(value)}")
    }
}

Animating Int and Offset

The family extends beyond floats and colors. Use animateIntAsState for whole-number values like a badge count target, and animateOffsetAsState or animateIntOffsetAsState to animate 2D position in one call.

Here a chip slides diagonally by animating an IntOffset.

@Composable
fun SlidingChip(moved: Boolean) {
    val pos by animateIntOffsetAsState(
        targetValue = if (moved) IntOffset(120, 60) else IntOffset.Zero,
        label = "pos"
    )
    Box(
        Modifier
            .offset { pos }
            .size(40.dp)
            .background(Color.Magenta)
    )
}

Quick Check

You want to smoothly animate a box's width, measured in Dp, when a boolean changes. Which API fits best?

Answer it in the interactive lesson

Recap: animate*AsState

The animate*AsState family is your go-to for animating a single value:

Pick the typed variant: animateFloatAsState, animateDpAsState, animateColorAsState, etc.
Set a targetValue; the result animates toward it on every change.
Tune motion with animationSpec using tween + easing or spring.
Combine several to animate multiple properties together.
Use finishedListener to react when an animation completes.

Next: animating content appearing and disappearing with AnimatedVisibility and transitions.

Free to start

Learn Kotlin with an AI tutor — free

Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.

Courses: 36
Lessons: 152

Start learning free View the full course

Frequently Asked Questions

Is the “animate*AsState Basics” lesson free?

Yes — any 3 lessons of the Android Academy learning path, including “animate*AsState Basics”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Android Academy course includes 4 lessons in total.

What will I learn in “animate*AsState Basics”?

Smoothly animate single values. You practise Android Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Android Academy?

No prior experience is required. Android Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.

How long does the “animate*AsState Basics” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Android Academy lesson?

Yes. Every Android Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

← Back to Android Academy