Show progress in the taskbar

The icon of the application in the taskbar or the Dock can show how far a long task is, and a count such as the number of unread notes, so the user sees both without opening the window. In this guide, an export fills the bar on the icon, and a button puts a count on it.

Show progress from Java

public class Taskbar {
  public static void main(String[] args) {
    Application.launch(
        WindowParameters.of("Export", 560, 360),
        window -> {
          Application application = window.application();
          window.bind(
              "export",
              Void.class,
              _ -> {
                for (int step = 1; step <= 10; step++) {
                  Taskbar.pause(800);
                  application.progress(step / 10.0);
                  window.emit("progress", step * 10);
                }
                application.progress(TaskbarProgress.none());
                return null;
              });
          window.bind(
              "unread",
              Integer.class,
              count -> {
                application.badgeCount(count);
                return null;
              });
          window.loadResource("taskbar/index.html");
        });
  }

  private static void pause(long millis) {
    try {
      Thread.sleep(millis);
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
    }
  }
}

The progress stays on the icon until the next call. TaskbarProgress has a form for each state:

Call	What the icon shows
progress(0.4) or progress(TaskbarProgress.of(0.4))	A bar at 40 %
progress(TaskbarProgress.indeterminate())	A bar that moves without an end
progress(TaskbarProgress.paused(0.4))	A paused bar, yellow on Windows
progress(TaskbarProgress.error(0.4))	A failed bar, red on Windows
progress(TaskbarProgress.none())	No bar
badgeCount(3)	The count 3; badgeCount(0) takes it away

The progress and the count belong to the application, not to one window: every window shows them where the platform shows one per window, and a window that opens later shows them too.

Show progress from the page

The page sets the same with lwjwae.taskbar:

await lwjwae.taskbar.progress(0.4);                            // a bar at 40 %
await lwjwae.taskbar.progress({ state: "paused", value: 0.4 }); // none, normal, indeterminate, paused, or error
await lwjwae.taskbar.progress(null);                           // no bar
await lwjwae.taskbar.badge(3);                                 // 0 for none

Platforms

Platform	Progress	Count
Windows	The button of every window, through ITaskbarList3.	A red circle with the number over the button, 9+ from 10 on, through SetOverlayIcon. The taskbar shows it only with its small buttons off, which is the default.
macOS	A bar over the icon in the Dock, the same in every state. An indeterminate bar stands still.	The badge of the icon in the Dock.
Linux	The com.canonical.Unity.LauncherEntry signal over D-Bus. The task manager of KDE Plasma and the dock of Ubuntu show it. An indeterminate bar shows nothing, and an error asks for attention.	The count of the same signal.

Good to know

• On Linux, the signal names the desktop entry of the program, NAME.desktop, as the Gradle plugin installs it. Under ./gradlew run, the desktop has no entry for the application, so the icon shows nothing.
• The bar on the page and the bar on the icon are separate: update both, as the export here does with its progress event.