systray example: if there is no system tray, allow waiting for one

Demonstrate that QSystemTrayIcon can wait for a tray to become
available. For example QDBusTrayIcon::init() connects to
QDBusServiceWatcher::serviceRegistered to detect the StatusNotifier
service becoming available. So instead of unconditionally quitting
if there is no tray, allow the user to choose to "Ignore" its absence,
or "Close" the application. Realistically, applications in which a tray
icon is an optional feature should not quit just because there's no
tray.

Task-number: QTBUG-94871
Change-Id: Ia8efd95fcfb9ff7c915ee8e259e9a0903fa7bcb3
Pick-to: 6.8 6.7 6.5
Reviewed-by: Axel Spoerl <[email protected]>
Reviewed-by: Ilya Fedin <[email protected]>
Reviewed-by: Dmitry Shachnev <[email protected]>

1 files changed, 6 insertions, 4 deletions

diff --git a/examples/widgets/desktop/systray/main.cpp b/examples/widgets/desktop/systray/main.cpp
index d13bde11ceb..37f6809a331 100644
--- a/examples/widgets/desktop/systray/main.cpp
+++ b/examples/widgets/desktop/systray/main.cpp
@@ -13,10 +13,12 @@ int main(int argc, char *argv[])
     QApplication app(argc, argv);
 
     if (!QSystemTrayIcon::isSystemTrayAvailable()) {
-        QMessageBox::critical(nullptr, QObject::tr("Systray"),
-                              QObject::tr("I couldn't detect any system tray "
-                                          "on this system."));
-        return 1;
+        auto choice = QMessageBox::critical(nullptr, QObject::tr("Systray"),
+            QObject::tr("I couldn't detect any system tray on this system."),
+            QMessageBox::Close | QMessageBox::Ignore);
+        if (choice == QMessageBox::Close)
+            return 1;
+        // Otherwise "lurk": if a system tray is started later, the icon will appear.
     }
     QApplication::setQuitOnLastWindowClosed(false);