Compose Timer - Android Dev Challenge

androidkotlinjetpack-composecanvasanimationslottieandroid-dev-challenge
Kotlin GitHub

Android Dev Challenge Week 2

After successfully completing the first week’s pet adoption challenge, I was eager to tackle Week 2: build a countdown timer app. This time, the focus was on animations - a perfect opportunity to explore Compose’s animation capabilities.

Design Inspiration

The UI was inspired by Playsharp’s Countdown design on Dribbble - a clean, modern timer with satisfying visual feedback.

Timer Initial State
Timer Initial State
Timer Running
Timer Running

Technical Highlights

Canvas Drawing

The circular progress indicator is drawn directly on a Canvas, giving full control over the animation:

@Composable
fun TimerCircle(progress: Float, modifier: Modifier = Modifier) {
    Canvas(modifier = modifier.size(200.dp)) {
        // Background circle
        drawArc(
            color = Color.Gray.copy(alpha = 0.3f),
            startAngle = -90f,
            sweepAngle = 360f,
            useCenter = false,
            style = Stroke(width = 12.dp.toPx(), cap = StrokeCap.Round)
        )


        // Progress arc
        drawArc(
            color = Color.Blue,
            startAngle = -90f,
            sweepAngle = 360f * progress,
            useCenter = false,
            style = Stroke(width = 12.dp.toPx(), cap = StrokeCap.Round)
        )
    }
}

Text Animations

The countdown numbers animate smoothly with scale and fade effects:

@Composable
fun AnimatedNumber(number: Int) {
    val scale by animateFloatAsState(
        targetValue = 1f,
        animationSpec = spring(
            dampingRatio = Spring.DampingRatioMediumBouncy,
            stiffness = Spring.StiffnessLow
        )
    )


    Text(
        text = number.toString(),
        modifier = Modifier.scale(scale),
        style = MaterialTheme.typography.h1
    )
}

Lottie Integration

For celebratory moments (like timer completion), Lottie animations add that extra polish:

@Composable
fun CompletionAnimation() {
    val composition by rememberLottieComposition(
        LottieCompositionSpec.RawRes(R.raw.confetti)
    )
    val progress by animateLottieCompositionAsState(composition)


    LottieAnimation(
        composition = composition,
        progress = { progress }
    )
}

Compose Animation Learnings

This project deepened my understanding of Compose animations:

  1. animateFloatAsState - Simple value animations
  2. updateTransition - Coordinated animations for state changes
  3. Canvas - Custom drawing with full control
  4. Lottie - Complex animations from After Effects

Animation Specs

// Spring animation for bouncy effects
spring(dampingRatio = 0.5f, stiffness = 300f)


// Tween for predictable timing
tween(durationMillis = 500, easing = FastOutSlowInEasing)


// Keyframes for complex sequences
keyframes {
    durationMillis = 1000
    0f at 0
    0.5f at 500
    1f at 1000
}

What I Learned

  1. Canvas is powerful - For custom graphics, nothing beats direct Canvas drawing
  2. Animation composition - Compose makes it easy to layer multiple animations
  3. State-driven animations - Animations react to state changes naturally
  4. Lottie integration - Easy to add professional animations with the Lottie library

Resources