Rotary input with Compose

Rotary input refers to input from pieces of your watch that spin or rotate. On average, users spend only a few seconds interacting with their watch. You can enhance your user experience by using Rotary input to allow your user to quickly accomplish various tasks.

The three main sources of rotary input on most watches include the rotating side button (RSB), and either a physical bezel or a touch bezel, which is a circular touch zone around the screen. Though expected behavior may vary based on the type of input, be sure to support rotary input for all essential interactions.

Scroll indicator

Most users expect apps to support the scroll gesture. As the content scrolls on the screen, give the users visual feedback in response to rotary interactions. Visual feedback can include scrolling indicators for vertical scroll or page indicators.

ScalingLazyColumn, TransformingLazyColumn and Picker support the scroll gesture by default, if you place these components inside AppScaffold and ScreenScaffold and pass the list state between ScreenScaffold and the component, such as a TransformingLazyColumn.

AppScaffold and ScreenScaffold provides the basic layout structure for Wear OS apps and already has a slot for a scroll indicator with a default implementation. To customize the scrolling progress, create a scroll indicator based on the list state object, as shown in the following code snippet:

val listState = rememberTransformingLazyColumnState()
ScreenScaffold(
    scrollState = listState,
    scrollIndicator = {
        ScrollIndicator(state = listState)
    }
) {
    // ...
}
Rotary.kt

You can configure a snap behavior for ScalingLazyColumn by using ScalingLazyColumnDefaults.snapFlingBehavior, as shown in the following code snippet:

val listState = rememberScalingLazyListState()
ScreenScaffold(
    scrollState = listState,
    scrollIndicator = {
        ScrollIndicator(state = listState)
    }
) {

    val state = rememberScalingLazyListState()
    ScalingLazyColumn(
        modifier = Modifier.fillMaxWidth(),
        state = state,
        flingBehavior = ScalingLazyColumnDefaults.snapFlingBehavior(state = state)
    ) {
        // Content goes here
        // ...
    }
}
Rotary.kt

Custom actions

You can also create custom actions that respond to rotary input in your app. For example, use rotary input to zoom in and out or to control volume in a media app.

If your component doesn't natively support scrolling events such as volume control, you can handle scroll events yourself.

The first step is to create a custom state managed in view model, and a custom callback that is used to process rotary scroll events.

class VolumeRange(
    val max: Int = 10,
    val min: Int = 0
)

private object VolumeViewModel {
    class MyViewModel : ViewModel() {
        private val _volumeState = mutableIntStateOf(0)
        val volumeState: State<Int>
            get() = _volumeState

        // ...
        fun onVolumeChangeByScroll(pixels: Float) {
            _volumeState.value = when {
                pixels > 0 -> minOf(volumeState.value + 1, VolumeRange().max)
                pixels < 0 -> maxOf(volumeState.value - 1, VolumeRange().min)
                else -> volumeState.value
            }
        }
    }
}
Rotary.kt

Then, use the callback once you receive the events, as shown in the following snippet.

val focusRequester: FocusRequester = remember { FocusRequester() }
val volumeViewModel: VolumeViewModel.MyViewModel =
    viewModel()
val volumeState by volumeViewModel.volumeState

TransformingLazyColumn(
    modifier = Modifier
        .fillMaxSize()
        .onRotaryScrollEvent {
            volumeViewModel.onVolumeChangeByScroll(it.verticalScrollPixels)
            true
        }
        .focusRequester(focusRequester)
        .focusable(),
) {
    // You can use volumeState here, for example:
    item {
        Text("Volume: $volumeState")
    }
}
Rotary.kt

Note that for the sake of simplicity, the preceding example uses pixel values that, if actually used are likely to be overly sensitive.