Compose previews

A composable is defined by a function and annotated with @Composable:

@Composable
fun SimpleComposable() {
    Text("Hello World")
}
AndroidStudioComposeSnippets.kt

To enable a preview of this composable, create another composable, annotated with @Composable and @Preview. This new, annotated composable now contains the composable you created initially, SimpleComposable:

@Preview
@Composable
fun SimpleComposablePreview() {
    SimpleComposable()
}
AndroidStudioComposeSnippets.kt

The @Preview annotation tells Android Studio that this composable should be shown in the design view of this file. Starting with Android Studio Electric Eel, you can see live updates to your composable preview as you make your edits.

You can add parameters manually in your code to customize the way Android Studio renders @Preview. You can even add the @Preview annotation to the same function multiple times to preview a composable with different properties.

One of the primary benefits of using @Preview composables is to avoid reliance on the emulator in Android Studio. You can save the memory-heavy startup of the emulator for more final look-and-feel changes, and @Preview's ability to make and test small code changes with ease.

To leverage @Preview annotation most effectively, make sure to define your screens in terms of the state it receives as input and the events that it outputs. In addition to improved testability, your screens render without a problem in your preview!

@Preview features

Android Studio offers some features to extend composable previews. You can change their container design, interact with them, or deploy them directly to an emulator or device.

LocalInspectionMode

You can read from the LocalInspectionMode CompositionLocal to see if the composable is rendered in a preview (inside an inspectable component). If the composition is rendered in a preview, LocalInspectionMode.current evaluates to true. This information lets you customize your preview; for example, you can show a placeholder image in the preview window instead of showing real data.

@Composable
fun GreetingScreen(name: String) {
    if (LocalInspectionMode.current) {
        // Show this text in a preview window:
        Text("Hello preview user!")
    } else {
        // Show this text in the app:
        Text("Hello $name!")
    }
}
AndroidStudioComposeSnippets.kt

Interactive mode

The interactive mode lets you interact with a preview similarly to how you would on a device running your program, like a phone or tablet. The interactive mode is isolated in a sandbox environment (meaning, isolated from other previews), where you can click elements and enter user input in the preview. It's a quick way to test different states, gestures, and even animations of your composable.

Preview interactive mode runs directly inside Android Studio without an emulator running, which results in some limitations:

• No network access
• No file access
• Some Context APIs may not be fully available

Deploy preview

You can deploy a specific @Preview to an emulator or physical device. The preview is deployed within the same project app as a new activity, so it shares the same context and permissions. It does not require you to write boilerplate code asking for a permission if it has already been granted!

Click the Deploy to Device icon next to the @Preview annotation or at the top of the preview, and Android Studio deploys that @Preview to your connected device or emulator.

Use with different devices

In Android Studio Electric Eel, you can edit the device parameter of the Preview annotation to define configurations for your composables in different devices.

When the device parameter has an empty string (@Preview(device = "")), you can invoke autocomplete by pressing Ctrl + Space. Then, you can set the values of each parameter.

From autocomplete, you can select any device option from the list–for example, @Preview(device = "id:pixel_4"). Alternatively, you can enter a custom device by choosing spec:width=px,height=px,dpi=int… to set the individual values of each parameter.

To apply, press Enter, or cancel with Esc.

If you set an invalid value, the declaration is underlined in red and a fix may be available (Alt + Enter (⌥ + ⏎ for macOS) > Replace with …. The Inspection attempts to provide a fix that is closest to resembling your input.

Multipreview annotations

With multipreview, you can define an annotation class that itself has multiple @Preview annotations with different configurations. Adding this annotation to a composable function automatically renders all of the different previews at once. For example, you can use this annotation to preview multiple devices, font sizes, or themes at the same time without repeating those definitions for every single composable.

Start by creating your own custom annotation class:

@Preview(
    name = "small font",
    group = "font scales",
    fontScale = 0.5f
)
@Preview(
    name = "large font",
    group = "font scales",
    fontScale = 1.5f
)
annotation class FontScalePreviews
AndroidStudioComposeSnippets.kt

You can use this custom annotation for your preview composables:

@FontScalePreviews
@Composable
fun HelloWorldPreview() {
    Text("Hello World")
}
AndroidStudioComposeSnippets.kt

You can combine multiple multipreview annotations and normal preview annotations to create a more complete set of previews. Combining multipreview annotations doesn't mean all the different combinations are shown. Instead, each multipreview annotation acts independently and renders only its own variants.

@Preview(
    name = "Spanish",
    group = "locale",
    locale = "es"
)
@FontScalePreviews
annotation class CombinedPreviews

@CombinedPreviews
@Composable
fun HelloWorldPreview2() {
    MaterialTheme { Surface { Text(stringResource(R.string.hello_world)) } }
}
AndroidStudioComposeSnippets.kt

The mix-and-match nature of multipreview-- and normal preview!-- lets you more comprehensively test many properties of larger scale projects.

Code navigation and composable outlines

You can hover over a preview to see the outlines of the composables contained within. Clicking on a composable outline triggers your editor view to navigate to its definition.

Copy @Preview render

Every rendered preview can be copied as an image by right clicking on it.

Set background color

By default, your composable is displayed with a transparent background. To add a background, add the showBackground and backgroundColor parameters. Keep in mind that backgroundColor is an ARGB Long, not a Color value:

@Preview(showBackground = true, backgroundColor = 0xFF00FF00)
@Composable
fun WithGreenBackground() {
    Text("Hello World")
}
AndroidStudioComposeSnippets.kt

Dynamic color preview

If you've enabled dynamic color in your app, use the wallpaper attribute to switch wallpapers and see how your UI reacts to different users' chosen wallpaper. Select from the different wallpaper themes offered by the Wallpaper class. This feature requires Compose 1.4.0 or higher.

Dimensions

By default, @Preview dimensions are chosen automatically to wrap its content. If you want to set the dimensions manually, you can add heightDp and widthDp parameters. Keep in mind those values are already interpreted as dp-- you don't need to add .dp at the end of the value:

@Preview(widthDp = 50, heightDp = 50)
@Composable
fun SquareComposablePreview() {
    Box(Modifier.background(Color.Yellow)) {
        Text("Hello World")
    }
}
AndroidStudioComposeSnippets.kt

Locale

To test different user locales, you need to add the locale parameter:

@Preview(locale = "fr-rFR")
@Composable
fun DifferentLocaleComposablePreview() {
    Text(text = stringResource(R.string.greeting))
}
AndroidStudioComposeSnippets.kt

System UI

If you need to display the status and action bars inside a preview, add the showSystemUi parameter:

@Preview(showSystemUi = true)
@Composable
fun DecoratedComposablePreview() {
    Text("Hello World")
}
AndroidStudioComposeSnippets.kt

UI mode

The parameter uiMode can take any of the Configuration.UI_* constants and allows you to change the behavior of the preview accordingly. For example, you can set the preview to Night Mode to see how the theme reacts.

@Preview and large data sets

Very often, a need arises where you must pass a large dataset to your composable preview. To do this, simply pass sample data to a Composable Preview function by adding a parameter with the @PreviewParameter annotation.

@Preview
@Composable
fun UserProfilePreview(
    @PreviewParameter(UserPreviewParameterProvider::class) user: User
) {
    UserProfile(user)
}
AndroidStudioComposeSnippets.kt

To provide the sample data, create a class that implements PreviewParameterProvider and returns the sample data as a sequence.

class UserPreviewParameterProvider : PreviewParameterProvider<User> {
    override val values = sequenceOf(
        User("Elise"),
        User("Frank"),
        User("Julia")
    )
}
AndroidStudioComposeSnippets.kt

This renders one preview per data element in the sequence:

You can use the same provider class for multiple previews. If necessary, limit the number of previews by setting the limit parameter.

@Preview
@Composable
fun UserProfilePreview2(
    @PreviewParameter(UserPreviewParameterProvider::class, limit = 2) user: User
) {
    UserProfile(user)
}
AndroidStudioComposeSnippets.kt

Annotation class @Preview

You can always 'command + click' the @Preview annotation in Android Studio for a full list of parameters that can be adjusted when customizing your preview.

annotation class Preview(
    val name: String = "",
    val group: String = "",
    @IntRange(from = 1) val apiLevel: Int = -1,
    val widthDp: Int = -1,
    val heightDp: Int = -1,
    val locale: String = "",
    @FloatRange(from = 0.01) val fontScale: Float = 1f,
    val showSystemUi: Boolean = false,
    val showBackground: Boolean = false,
    val backgroundColor: Long = 0,
    @UiMode val uiMode: Int = 0,
    @Device val device: String = Devices.DEFAULT
)
AndroidStudioComposeSnippets.kt

Additional resources

To read more about how Android Studio promotes @Preview ease of use, and more Tooling tips, check out the blog Compose Tooling.