compose-autotransition

Status: Experimental

A simple library for automatically animating between Compose states.

var scale by remember { mutableStateOf(1f) }
var elevation by remember { mutableStateOf(0.dp) }

with(rememberAutoTransition()) {
    Button(onClick = {
        withAnimation {
            scale = 0.5f
            elevation = 8.dp
        }
    }) { /* … */ }
}

The main component of this library is the AutoTransition.withAnimation function, which takes a block and animates changes to any snapshot state objects (such as those created by mutableStateOf) written to inside the block. Use the rememberAutoTransition() Composable function to get an instance of AutoTransition.

withAnimation uses Compose's snapshot system to determine what state you changed in the block and then launches a coroutine to animate it. It does this by running the block in a snapshot, then disposing the snapshot without applying it. Since the snapshot is never applied, it's important to not perform side effects in the withAnimation block, or to write to any states not backed by snapshot state.

Demo

Customization

By default, withTransition can animate changes to any MutableState objects holding values of types that Compose ships with TwoWayConverter vector converters for. This set is defined in DefaultAdapters.kt. To specify how to handle additional types (either additional state object types or value types inside MutableStates), provide a custom AutoTransitionFactory using AutoTransitionFactory.Builder and LocalAutoTransitionFactory.

Here's an example of providing an adapter for a custom value type:

class Temp(val degrees: Float)

@Composable
fun App() {
    val factory = remember {
        AutoTransitionFactory.Builder()
            .addAdapterRegistry(MutableStateAdapter(
                Temp::class,
                TwoWayConverter(
                    convertToVector = { /* … */ },
                    convertFromVector = { /* … */ }
                )
            ))
            .build()
    }

    CompositionLocalProvider(LocalAutoTransitionFactory provides factory) {
        // Rest of app.
        HomeScreen()
    }
}

@Composable
fun HomeScreen() {
    with(rememberAutoTransition()) {
        // …
    }
}

The AutoTransitionFactory.Builder can also override the default animation spec.

TODO

• Write docs.
• Release on Maven.
• Support multiplatform.