swing-ui/org.jetbrains.compose.swing.tooling/Preview

Preview

@Target(allowedTargets = [AnnotationTarget.FUNCTION, AnnotationTarget.ANNOTATION_CLASS])

annotation class Preview(val name: String = "", val widthPx: Int = -1, val heightPx: Int = -1, val lookAndFeel: String = "")

Marks a composable that an IDE may render on its own, so a component can be seen without running the application.

The composable must take no parameters: nothing supplies arguments to it.

A PreviewEnvironment on the same classpath prepares the process every preview in it renders under; what this annotation states is what that preview alone needs on top.

@Preview(lookAndFeel = "javax.swing.plaf.nimbus.NimbusLookAndFeel")
@Composable
fun LoginFormPreview() = LoginForm(user = "", onSubmit = {})

Rendering one composable several ways. Repeat the annotation, and the composable is rendered once per occurrence, each under what that occurrence states:

@Preview(name = "Metal", lookAndFeel = "javax.swing.plaf.metal.MetalLookAndFeel")
@Preview(name = "Nimbus", lookAndFeel = "javax.swing.plaf.nimbus.NimbusLookAndFeel")
@Composable
fun LoginFormPreview() = LoginForm(user = "", onSubmit = {})

A set worth repeating belongs on an annotation class of its own, which then stands for every occurrence it carries. Annotating a composable with it renders all of them, and an annotation class may carry others, so sets compose:

@Preview(name = "Metal", lookAndFeel = "javax.swing.plaf.metal.MetalLookAndFeel")
@Preview(name = "Nimbus", lookAndFeel = "javax.swing.plaf.nimbus.NimbusLookAndFeel")
annotation class PreviewLookAndFeels

@PreviewLookAndFeels
@Composable
fun LoginFormPreview() = LoginForm(user = "", onSubmit = {})

Such sets are the application's to declare: the look and feels a preview is worth seeing under are its own to choose, and the library cannot name them for it.

Properties

heightPx

val heightPx: Int

the height, in pixels, to lay the content out at. Defaults to -1, meaning the height the content takes at the width it ends up with, so that content which wraps is as tall as its wrapping makes it.

lookAndFeel

val lookAndFeel: String

the fully-qualified class name of the javax.swing.LookAndFeel to install before the content is composed. The class is loaded by name off the classpath the preview is rendered on, so anything but the JDK's own look and feels has to be a dependency of the module the preview is declared in. Defaults to the empty string, meaning whatever the PreviewEnvironment left installed.

name

val name: String

the label this rendering is shown under. Defaults to the empty string, meaning the function's own name where it is rendered one way, and its position where it is rendered several.

widthPx

val widthPx: Int

the width, in pixels, to lay the content out at. Defaults to -1, meaning the content's own preferred width, within whatever room the preview is shown in. A width and a height are two parameters because an annotation cannot hold a java.awt.Dimension.