systray-util

A library for Windows 10 and 11 for monitoring and interacting with native system tray icons.

Example usage

fn main() -> systray_util::Result<()> {
  let mut systray = Systray::new()?;

  // Alternatively use `systray.events().await` to get async events for use
  // with a Tokio runtime.
  while let Some(event) = systray.events_blocking() {
    match event {
      SystrayEvent::IconAdd(icon) => {
        println!("Tray icon added: {:?}", icon);
      }
      SystrayEvent::IconUpdate(icon) => {
        println!("Tray icon updated: {:?}", icon);
      }
      SystrayEvent::IconRemove(id) => {
        println!("Tray icon removed: {:?}", id);
      }
    }
  }

  // Send click action to first icon.
  if let Some(icon) = systray.icons().first() {
    systray.send_action(&icon.stable_id, &SystrayIconAction::LeftClick)?;
  }

  Ok(())
}

Technical overview

Uses a "spy" window that intercepts system tray messages directed to Shell_TrayWnd. This is done by creating a hidden window with the same class name as Shell_TrayWnd and processing WM_COPYDATA messages that contain tray icon data (additions, updates, removals).

When a 3rd-party application uses Shell_NotifyIcon to add, update, or remove a tray icon, the code inside Shell32.dll sends a WM_COPYDATA message to the Windows taskbar window. It does this by calling FindWindow and looking for a window with the class name of Shell_TrayWnd.

WM_COPYDATA messages

• 1: Appbar messages. Invoked via SHAppBarMessage.
  • Affects the position of shell flyouts (e.g. volume and wifi flyouts) and fullscreen behavior of windows.
• 2: Tray update messages: tray icon additions, updates, and removals. Invoked via Shell_NotifyIcon.
  • Necessary for detection of tray icons.
• 3: Icon position requests. Invoked via Shell_NotifyIconGetRect.
  • Affects the position of dropdowns for some tray icons (e.g. OneDrive).