Using jSystemThemeDetector with Swing

[SturmB]

I am very much looking forward to using this library to add a dark mode to my little project. It seems to take care of the "detect if the OS is in Dark Mode" portion, but now I need to know how to change my Java app to a dark theme to follow along with the OS.

What is the preferred way of changing a Java Swing app's theme? Will I need a separate library? Is there a collection of different themes available somewhere from which I can choose an appropriate dark theme or will it be set automatically by the OS? I'm still quite new, as you can tell, and could use some direction.

[DevCharly]

I would try FlatLaf - https://github.com/JFormDesigner/FlatLaf 😉

[SturmB]

Cool, I'll definitely do that, thanks!

[SturmB]

So, I tried out @DevCharly's suggestion and it does seem to work. I have my code like so:

    public static void main(String[] args) {
        // Set the look and feel
        FlatCarbonIJTheme.install();
        final OsThemeDetector detector = OsThemeDetector.getDetector();
        detector.registerListener(isDark -> {
            if (isDark) {
                // The OS switched to a dark theme
                FlatCarbonIJTheme.install();
                FlatCarbonIJTheme.updateUI();
            } else {
                // The OS switched to a light theme
                FlatCyanLightIJTheme.install();
                FlatCyanLightIJTheme.updateUI();
            }
        });

        // Create the frame
        ArtDeptNew frame = new ArtDeptNew();
        [...]
    }

I hope this is the 'preferred' way of doing it.

[DevCharly]

Nearly perfect, but I think you should add SwingUtilities.invokeLater(...) to invoke to look and feel switching on the AWT/Swing thread. The detector listener is invoked on another thread as far as I know.

public static void main(String[] args) {
        // Set the look and feel
        FlatCarbonIJTheme.install();

        final OsThemeDetector detector = OsThemeDetector.getDetector();
        detector.registerListener(isDark -> {
          SwingUtilities.invokeLater(() -> {
            if (isDark) {
                // The OS switched to a dark theme
                FlatCarbonIJTheme.install();
            } else {
                // The OS switched to a light theme
                FlatCyanLightIJTheme.install();
            }
            FlatLaf.updateUI();
          });
        });

        // Create the frame
        ArtDeptNew frame = new ArtDeptNew();
        [...]
    }

I would also write FlatLaf.updateUI() instead of FlatCarbonIJTheme.updateUI() or FlatCyanLightIJTheme.updateUI().

[SturmB]

Thank you, that is really helpful! 😊

[Dansoftowner]

Yes! I would also add to the code:

public static void main(String[] args) {
        final OsThemeDetector detector = OsThemeDetector.getDetector();

        // Setting the base look and feel
        installTheme(detector.isDark());

        detector.registerListener(isDark -> {
          SwingUtilities.invokeLater(() ->  installTheme(isDark));
        });

        // Create the frame
        ArtDeptNew frame = new ArtDeptNew();
        [...]
}

private static void installTheme(boolean darkTheme) {
       if (darkTheme) {
            FlatCarbonIJTheme.install();
       } else {
          FlatCyanLightIJTheme.install();
       }
       FlatLaf.updateUI();
}

Because now the right theme will be detected on startup.