Compose Multiplatform doesn't ship file dialogs. Nucleus deliberately doesn't either — the community already shipped the right answer.

TL;DR

Use FileKit by @vinceglb.
Native pickers: NSOpenPanel/NSSavePanel on macOS, IFileOpenDialog/IFileSaveDialog on Windows, xdg-desktop-portal on Linux.
Nucleus ships preloaded GraalVM reachability metadata for FileKit — Native Image just works.

Install

dependencies {
    implementation("io.github.vinceglb:filekit-compose:<version>")
}

Quickstart

val launcher = rememberFilePickerLauncher(
    type = PickerType.File(extensions = listOf("png", "jpg")),
    title = "Pick an image",
) { file ->
    // file: PlatformFile?
}

Button(onClick = { launcher.launch() }) {
    Text("Pick image")
}

How it works

FileKit drives the real native dialog on each OS:

macOS — NSOpenPanel / NSSavePanel via Cocoa.
Windows — IFileOpenDialog / IFileSaveDialog via JNA COM.
Linux — xdg-desktop-portal FileChooser, with GTK / zenity fallbacks.

File type filters with descriptions, single-file / multi-file / folder / save modes, a Compose-friendly API (rememberFilePickerLauncher), and a cross-platform PlatformFile abstraction with read/write/metadata helpers.

GraalVM native image — zero config

The Nucleus Gradle plugin ships preloaded reachability metadata for FileKit as part of its library metadata bundle. The metadata is conditionally included only when io.github.vinceglb.filekit is on your runtime classpath, and covers:

macOS Foundation proxy + callback types (FoundationLibrary, ID, runnable callbacks).
Windows JNA COM bindings (FileDialog, FileOpenDialog, FileSaveDialog, ShellItem, Shell32, COMDLG_FILTERSPEC, PROPERTYKEY, …).
XDG desktop-portal D-Bus proxy (FileChooserDbusInterface) for Linux.

If you package with the Nucleus plugin and target native-image, FileKit works out of the box — no manual reachability-metadata.json, no tracing-agent run required.

Why Nucleus doesn't ship this

FileKit already covers the full surface natively, has active maintenance, and integrates cleanly with Compose state. Reimplementing it inside Nucleus would duplicate effort with no benefit.

Native file dialogs