developing-with-compose-previews

Developing With Compose Previews — Preview-Driven Development

@Preview is the cheapest verification loop in Compose: edit, see the render in ~1 s, no build/install/navigate cycle. It only pays off if composables are structured so previews stay alive — hoisted state, no ViewModel in the signature, realistic sample data. This skill encodes that structure and the anti-patterns that cause teams to abandon previews. For taking those previews as on-device screenshots in CI, see ../capturing-preview-screenshots-in-ci/SKILL.md.

When to use this skill

A @Preview "fails to render" or crashes because the composable takes a ViewModel, repository, or Context-bound dependency.
The user wants to see loading / empty / error / overflow-text / RTL states without running the app — @PreviewParameter territory.
A composable loads images with Coil/Glide and the preview shows nothing — needs LocalInspectionMode.
The user asks "how should I structure Compose previews so they don't keep breaking" or mentions "preview-driven development".
Previews exist but drift out of date / show the "out of date" banner constantly and the team is about to delete them.

When NOT to use this skill

The user wants to capture previews as screenshots on a device or in CI (HotSwan captureAllPreviews, GitHub Pages catalog) — use ../capturing-preview-screenshots-in-ci/SKILL.md.
The user wants pixel-diff golden-image regression tests (Paparazzi / Roborazzi) — that is a different tool; see ../capturing-preview-screenshots-in-ci/SKILL.md for where it fits relative to device rendering.
The user is writing behavioral UI tests (ComposeTestRule, finders, assertions) — start at ../../setup/configuring-test-dependencies/SKILL.md and ../../finders/finding-nodes-by-tag-text-content/SKILL.md.

Prerequisites

androidx.compose.ui:ui-tooling-preview on the main classpath (provides @Preview, @PreviewParameter, PreviewParameterProvider; see compose/ui/ui-tooling-preview/), plus debugImplementation("androidx.compose.ui:ui-tooling") so Android Studio can render.
LocalInspectionMode ships in androidx.compose.ui:ui (compose/ui/ui/.../platform/InspectionMode.kt — staticCompositionLocalOf { false }), no extra dependency.
A Compose-enabled module (the org.jetbrains.kotlin.plugin.compose plugin or buildFeatures.compose = true).

Workflow

1. Decide what to preview: the component, not the screen. Screen-level composables pull in ViewModels, navigation, DI — they are the hardest to preview and the least worth it. Preview the leaf and mid-level composables that take plain parameters; the screen composable wires those together and does not need its own @Preview.
2. Hoist state until the previewable composable takes only plain values. If a composable's signature mentions a ViewModel, split it: a stateful wrapper at the call site that owns the ViewModel, and a stateless composable that takes the data. Preview the stateless one. (See Pattern: ViewModel in the signature.)
3. Wrap the preview body in your app theme. A composable that reads MaterialTheme.colorScheme / .typography renders with default Material values unless wrapped — the preview then lies about how it looks shipped. Always AppTheme { … } (or your equivalent) inside the @Preview function.
4. Give the preview a realistic viewport when the composable expands. A composable using Modifier.fillMaxWidth() collapses to zero width in a wrap-content preview. Add @Preview(widthDp = 360) (and heightDp if it fills height) so it renders at a believable size.
5. Use realistic sample data, not "Lorem ipsum". Sample data should match the production model's shape and edge cases (long names, empty strings, zero-item lists). When the model changes, the preview should fail to compile — that compile error is the feature: it tells you the preview (and the doc it represents) is stale.
6. Cover every UI state with @PreviewParameter. Render loading / content / empty / error / overflow side by side from one function via a PreviewParameterProvider. (See Pattern: one state per preview.)
7. Fan out across configurations with repeated @Preview. @Preview is @Repeatable — stack uiMode = UI_MODE_NIGHT_YES, fontScale = 1.5f, device = "spec:width=320dp,height=640dp", locale = "ar" (RTL). Each annotation is one render. For sets you reuse across many composables, define a custom annotation class annotated with the @Previews and apply that one annotation ("multipreview").
8. Quarantine unavoidable dependencies behind LocalInspectionMode. Image loaders need a Context and network access. Branch on LocalInspectionMode.current to draw a placeholder in preview. Use sparingly — if you reach for it everywhere, the composable still needs better state hoisting.

Patterns

Pattern: `ViewModel` in the signature

// WRONG
@Composable
fun ProfileScreen(viewModel: ProfileViewModel) {
    val user by viewModel.user.collectAsStateWithLifecycle()
    Column { Text(user.name); Text(user.bio) }
}

@Preview
@Composable
fun ProfileScreenPreview() {
    ProfileScreen(viewModel = ???)   // can't: needs repository, network, DB
}
// WRONG because: the preview environment has no DI graph. Studio must instantiate
// ProfileViewModel and its whole dependency chain, so the preview fails to compile
// or crashes at render time.

// RIGHT — stateless composable takes plain values; ViewModel stays at the call site
@Composable
fun ProfileScreen(viewModel: ProfileViewModel = hiltViewModel()) {
    val user by viewModel.user.collectAsStateWithLifecycle()
    ProfileContent(name = user.name, bio = user.bio, onEditClick = viewModel::onEdit)
}

@Composable
fun ProfileContent(name: String, bio: String, onEditClick: () -> Unit = {}) {
    Column { Text(name); Text(bio) }
}

@Preview(widthDp = 360)
@Composable
private fun ProfileContentPreview() {
    AppTheme { ProfileContent(name = "Jane Doe", bio = "Android developer") }
}

Pattern: one state per preview vs `@PreviewParameter`

// WRONG — three near-duplicate preview functions, easy to let one rot
@Preview @Composable fun UserCardLoadingPreview()  { AppTheme { UserCard(UiState.Loading) } }
@Preview @Composable fun UserCardContentPreview()  { AppTheme { UserCard(UiState.Content(sampleUser)) } }
@Preview @Composable fun UserCardErrorPreview()    { AppTheme { UserCard(UiState.Error("offline")) } }
// WRONG because: each state is a separate function with its own copy of the theme wrapper;
// adding a new state means remembering to add another function. Edge cases get skipped.

// RIGHT — one function, every state generated from the provider
class UserStateProvider : PreviewParameterProvider<UiState> {
    override val values = sequenceOf(
        UiState.Loading,
        UiState.Content(User(name = "Jane Doe", bio = "Short bio")),
        UiState.Content(User(name = "A very long display name that overflows the row", bio = "")),
        UiState.Empty,
        UiState.Error("network unavailable"),
    )
}

@Preview(widthDp = 360)
@Composable
private fun UserCardPreview(@PreviewParameter(UserStateProvider::class) state: UiState) {
    AppTheme { UserCard(state) }
}

Pattern: image loader with no `Context`

// WRONG
@Composable
fun UserAvatar(imageUrl: String) {
    AsyncImage(model = imageUrl, contentDescription = "Avatar", modifier = Modifier.size(48.dp))
}
// WRONG because: AsyncImage needs an ImageLoader (Context + network). In a preview it renders
// empty, so a composable built around the avatar looks broken in Studio for no real reason.

// RIGHT — branch on LocalInspectionMode for the preview-only path
@Composable
fun UserAvatar(imageUrl: String) {
    if (LocalInspectionMode.current) {
        Box(Modifier.size(48.dp).clip(CircleShape).background(MaterialTheme.colorScheme.surfaceVariant))
    } else {
        AsyncImage(
            model = imageUrl,
            contentDescription = "Avatar",
            modifier = Modifier.size(48.dp).clip(CircleShape),
        )
    }
}

Pattern: reusable preview set as a multipreview annotation

// WRONG — paste the same four @Preview lines onto every composable
@Preview(name = "phone")           // duplicated across dozens of files;
@Preview(name = "dark", uiMode = UI_MODE_NIGHT_YES)
@Preview(name = "font 1.5x", fontScale = 1.5f)
@Preview(name = "RTL", locale = "ar")
@Composable fun FooPreview() { AppTheme { Foo() } }
// WRONG because: when the standard set changes (add a tablet size, drop a font scale) you
// have to edit every composable. The set is policy; it belongs in one place.

// RIGHT — define once, apply once. @Preview can annotate an annotation class.
@Preview(name = "phone", showBackground = true)
@Preview(name = "dark", uiMode = Configuration.UI_MODE_NIGHT_YES, showBackground = true)
@Preview(name = "font 1.5x", fontScale = 1.5f, showBackground = true)
@Preview(name = "RTL", locale = "ar")
annotation class AppPreviews

@AppPreviews
@Composable
private fun FooPreview() { AppTheme { Foo() } }

Anti-patterns to flag in review

Screen-level @Preview. A @Preview on a composable that takes a ViewModel/NavController. Preview the components it composes instead.
Theme not wrapped. A preview body that calls a MaterialTheme-dependent composable without AppTheme { … } — it renders with default Material values, not the app's.
Zero-width preview. A composable using fillMaxWidth()/fillMaxSize() previewed without widthDp/heightDp — it collapses.
"Lorem ipsum" / fabricated data. Sample data that does not mirror the production model's shape and edge cases; it hides overflow and empty-state bugs and never forces a recompile when the model changes.
Mocking inside a preview. Mockito/MockK objects in a @Preview body. The need to mock means state was not hoisted; fix the composable, not the preview.

Mandatory rules

MUST keep previewable composables free of ViewModel, repository, NavController, and Context-bound parameters. Hoist that state to a stateful wrapper at the call site.
MUST wrap every @Preview body in the app theme when the composable reads MaterialTheme colors/typography/shapes.
MUST use @PreviewParameter + a PreviewParameterProvider to cover the full set of UI states (loading, content, empty, error, overflow) rather than one preview function per state.
MUST add widthDp/heightDp to @Preview for composables that fill width/height, so the render has a realistic viewport.
MUST use sample data that mirrors the production model — a model change should break the preview's compile, and that is intended.
MUST NOT put mocks (Mockito/MockK) in a @Preview body; MUST NOT sprinkle LocalInspectionMode checks as a substitute for hoisting state — reserve it for genuinely environment-bound calls (image loading, sensors).
PREFERRED: mark preview functions private; they are tooling entry points, not API.
PREFERRED: extract the team's standard configuration set into one @Preview-annotated annotation class (multipreview) and apply that.

Verification

No previewable composable takes a ViewModel/repository/Context parameter; git grep -nE '@Preview' -A3 -- '**/*.kt' shows preview bodies calling stateless composables only.
Every @Preview body that uses MaterialTheme.* is wrapped in the app theme.
State-bearing composables have a PreviewParameterProvider covering loading/content/empty/error/overflow; grep -rn "PreviewParameterProvider" src/ is non-empty for those modules.
Composables using fillMaxWidth/fillMaxSize have @Preview(widthDp = …).
No mock(/mockk( appears under a @Preview function.
Building the module after a model field rename causes the affected previews to fail compilation (proof the sample data is real, not Lorem).

References

developer.android.com/develop/ui/compose/tooling/previews — @Preview parameters, @PreviewParameter/PreviewParameterProvider, multipreview annotation classes, device spec strings.
androidx/compose/ui/ui-tooling-preview/src/commonMain/kotlin/androidx/compose/ui/tooling/preview/Preview.kt — the @Preview annotation (@Repeatable; name, group, widthDp, heightDp, locale, fontScale, showSystemUi, showBackground, backgroundColor, uiMode, device, wallpaper).
androidx/compose/ui/ui-tooling-preview/src/commonMain/kotlin/androidx/compose/ui/tooling/preview/PreviewParameter.kt — PreviewParameterProvider<T> (values: Sequence<T>, getDisplayName) and @PreviewParameter(provider, limit).
androidx/compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/platform/InspectionMode.kt — LocalInspectionMode = staticCompositionLocalOf { false }.
developer.android.com/develop/ui/compose/state-hoisting — state hoisting, stateful vs stateless composables.
hotswan.dev/blog/compose-preview-driven-development — skydoves, "Compose Preview Driven Development with Instant Feedback" (state hoisting for previewability, LocalInspectionMode, @PreviewParameter, anti-patterns, the preview-rebuild friction).
Sibling skill: ../capturing-preview-screenshots-in-ci/SKILL.md — rendering these previews as device screenshots and a CI catalog; where Paparazzi/Roborazzi fit.
Sibling skill: ../../setup/configuring-test-dependencies/SKILL.md — the Gradle matrix for Compose test/tooling artifacts.