These two are the clearest case in the framework of a capability that is not a property * of the platform. macOS has both since 29/09/2026, through AppKit's own share menu, and Windows 10+ * since 01/10/2026, through WinRT's DataTransferManager; Linux has a file dialog and no share sheet. * The browser has a picker always and a share sheet only in * some browsers, over HTTPS. So "am I on the web?" is the wrong question, and * {@link PlatformUtils#isSupported} is the right one — it is answered at runtime, per capability, * and two browsers on the same machine can answer it differently.
* *The picker is asynchronous, and has to be: the web build is single-threaded JavaScript, * so a blocking file dialog cannot exist on one of the four platforms. The callback arrives on the * paint thread, so it may touch the UI directly, as it does below.
* *The cancel is not an error and not a null: {@link FileChooser#open} answers with an * empty array. That is one branch, always present, and forgetting it is what produces a * screen that appears to do nothing when the user backs out of the dialog.
*/ public class R31Files extends Recipe { private Label answer; /** The last pick, kept so the share row has something to hand over. */ private FileChooser.PickedFile chosen; public String title() { return "Files, sharing and printing"; } public String note() { return "Ask the capability, not the platform. Phones, Windows 10+ and the Mac have the picker and" + " the share sheet; Linux has no share sheet; a browser has the picker always and the sheet only" + " sometimes." + " Printing takes a PDF, and every platform's own dialog does the rest."; } public void build(Component body) throws Exception { answer = label("Nothing chosen yet.", 1f, false, Styles.captionColor, Position.START); answer.testTag("files.answer"); // Pinned below the scrolling body, so the answer stays in view (see Recipe.pin). pin(answer); row(body, "files.choose", 0xE2C8, "Choose a file", PlatformUtils.isSupported(Capability.FILE_PICKER), () -> Capabilities.files() .open(new FileChooser.Options().title("Choose a file").extensions("pdf", "png", "jpg", "txt"), files -> { // The empty array IS the cancel. No null to check, and no exception to catch. if (files.length == 0) { said("Cancelled"); return; } chosen = files[0]; read(chosen); })); row(body, "files.share-link", 0xE80D, "Share a link", PlatformUtils.isSupported(Capability.SHARING), () -> Capabilities.sharing().text("CrossFly", "https://crossfly.dev")); // Sharing.bytes and not Sharing.file, and the difference is the whole lesson: a file the // user picked has no path on Android (it is a content:// document) and none at all in a // browser, so the path-shaped call cannot serve the most ordinary flow there is — pick // something, then send it. Handing over the content works on every platform that shares. row(body, "files.share-file", 0xE2C4, "Share the chosen file", PlatformUtils.isSupported(Capability.SHARING), () -> { if (chosen == null) { said("Choose a file first"); return; } try { Capabilities.sharing().bytes("CrossFly", chosen.name, chosen.bytes()); } catch (Exception e) { said("Could not share: " + e.getMessage()); } }); // Saving is NOT sharing, and the two rows sit together so the difference is visible: sharing // sends content somewhere else and never says where it went; saving puts a file under the // person's own control, with a name they picked, in a place they can find again. row(body, "files.save", 0xE161, "Save a file", PlatformUtils.isSupported(Capability.SAVE_FILE), () -> { byte[] content = chosen != null ? bytesOf(chosen) : "Saved by CrossFly.\n".getBytes(java.nio.charset.StandardCharsets.UTF_8); String name = chosen != null ? chosen.name : "crossfly.txt"; String mime = chosen != null ? chosen.mimeType() : "text/plain"; if (content == null) return; Capabilities.saver() .save(name, mime, content, (saved, error) -> said(saved ? "Saved " + name : error == null ? "Cancelled" : "Could not save: " + error)); }); // Printing is the third way out, and it takes a PDF because every platform's print system // already speaks PDF -- a receipt generated here and a boleto downloaded from a server // print through the same call. row(body, "files.print", 0xE8AD, "Print a receipt", PlatformUtils.isSupported(Capability.PRINTING), this::printReceipt); } /** * A receipt on an 80 mm roll, built with {@link Pdf} and handed to the system's print dialog. ** The answer has four values and the browser is why: a phone and a desktop say whether * the job was sent or cancelled, and a browser only says that its dialog closed. Treating * {@code CLOSED} as either of the other two would be the app guessing. */ private void printReceipt() { Pdf pdf = new Pdf(); pdf.page(Pdf.ROLL_80MM_WIDTH, 300); pdf.font(Pdf.COURIER_BOLD, 14).text(12, 270, "RECEIPT 4471"); // Amounts in reais on purpose: a Brazilian receipt, with the comma as decimal separator. pdf.font(Pdf.COURIER, 10).text(12, 250, "2 x Specialty coffee R$ 38,00"); pdf.font(Pdf.COURIER, 10).text(12, 235, "1 x Sugar 1 kg R$ 6,90"); pdf.lineWidth(1).line(12, 225, 215, 225); pdf.font(Pdf.COURIER_BOLD, 11).text(12, 208, "Total R$ 44,90"); Capabilities.printing().print("Receipt 4471",pdf.build(), (result, error) -> { switch (result) { case SENT: said("Sent to the printer"); break; case CANCELLED: said("Cancelled"); break; case CLOSED: said("The print dialog closed (this platform does not say whether it printed)"); break; default: said("Could not print: " + error); } }); } /** * The chosen file's bytes, or null after saying why not. * * @param f the chosen file * @return its content, or null */ private byte[] bytesOf(FileChooser.PickedFile f) { try { return f.bytes(); } catch (Exception e) { said("Could not read " + f.name + ": " + e.getMessage()); return null; } } /** * Proves the pick is real by reading it, which is the part that differs most between platforms: * a path on the desktop and on iOS, a content resolver on Android, an ArrayBuffer in a browser. */ private void read(FileChooser.PickedFile f) { try { int bytes = f.bytes().length; said(f.name + " — " + bytes + " bytes read, " + f.mimeType()); } catch (Exception e) { said(f.name + " — could not be read: " + e.getMessage()); } } /** * A row per capability. The button carries a {@code testTag} so a TestCase can drive it — which * on a phone is the only way in, since the whole UI is drawn on one GL surface and a device * automation tool sees a single view with no children inside it. * * @param tag stable name for the button, for tests * @param icone the Material glyph on the tile * @param name the row's label * @param available whether the platform has this capability * @param go what the button does */ private void row(Component body, String tag, int icone, String name, boolean available, Runnable go) throws Exception { Card c = new Card(); c.setLayout(new GridLayout(Position.START, Position.CENTER)); c.getStyle() .outgap(Gap.ofFont(0, 0, 0, .5f)); PalColor tom = available ? Tones.accent() : Tones.danger(); Component text = new Component(); text.setLayout(new VerticalLayout(Position.START, Position.START)); text.add(LAY_AUTO, label(name, 1.2f, true, Styles.textColor, Position.START)); text.add(LAY_AUTO, label(available ? "Ready" : "Not on this platform", 1f, true, tom, Position.START)); Button b = new Button(MaterialIcon.of(available ? 0xE5C8 : 0xE002, 1.4f)); b.setEnabled(available); b.testTag(tag); b.onAction(e -> go.run()); c.add(0f, 1f, 0f, Tones.tile(icone, tom), outgap(text, .6f, 0, 0, 0), b); body.add(LAY_AUTO, c); } private void said(String what) { // Also to the log, and not only to the label. This screen is the one people drive by hand on // a device or over ssh to find out whether a native capability actually worked -- and a // verdict that exists only as pixels is unreadable exactly then. It cost a round trip here: // a save that left no file on disk, with no way to tell a cancel from a failure. Debug.log("[files] " + what); answer.setText(what); answer.invalidateMeasure(); // the pinned band must grow with it (see Recipe.pin) Screen.repaint(); } }