I have a Java swing UI where I need to disable a button on the UI if I could not detect an active internet connection.

The code function properly so far, but when I get disconnected from the internet, it does not retrigger the method to update the boolean flag.

How can I add an event on that flag to let my button consume it during the lifetime of the application?

public class Main {
private static JButton button;
private static boolean testButtonEnabled;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            /*
             * function that returns true/false if connected to the internet
             */
            if(Utils.isConnectedToInternet()) {
                logger.debug("System is connected to the internet");
                testButtonEnabled=true;
            } else {
                logger.debug("System is not connected to the internet");
                testButtonEnabled=false;
            }

            Main window = new Main();
            window.frame.setVisible(true);  

            button = new JButton("my button");
            /* 
             * set the internet status
             */
            button.setVisible(testButtonEnabled);
        }
    }
}

}

CodePudding user response：

Again, this code:

SwingWorker<Void, String>  worker = new SwingWorker<Void, String>()
        {
            public Void doInBackground()
            {
                while(true)
                {
                    
                    try {
                        isConnectedToInternet = Utils.isConnectedToInternet();
                        if (isConnectedToInternet) {
                            btn_online2.setEnabled(isConnectedToInternet);
                        } else {
                            btn_online2.setEnabled(isConnectedToInternet);
                        }
                        logger.debug("Internet connection status: "   isConnectedToInternet);
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        worker.execute();

is dangerous since it makes mutational changes to a Swing component from a background thread. While this code may work 95% of the time, it can fail in unpredicatable ways and at unpredicatable times. Better to only mutate Swing components on the event thread. For instance, even this would be better:

SwingWorker<Void, String>  worker = new SwingWorker<Void, String>() {
    @Override
    public Void doInBackground() {
        while(true) {
            try {
                isConnectedToInternet = Utils.isConnectedToInternet();
                // note that there is no need for the if/else block
                SwingUtilities.invokeLater(() -> {
                    btn_online2.setEnabled(isConnectedToInternet);
                });
                logger.debug("Internet connection status: "   isConnectedToInternet);
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
};
worker.execute();

or better still, using SwingWorker's publish/process:

SwingWorker<Void, Boolean>  worker = new SwingWorker<Void, Boolean>() {
    @Override
    public Void doInBackground() {
        while(true) {
            try {
                isConnectedToInternet = Utils.isConnectedToInternet();
                // note that there is no need for the if/else block
                publish(Utils.isConnectedToInternet());
                logger.debug("Internet connection status: "   isConnectedToInternet);
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    @Override
    protected void process(List<Boolean> chunks) {
        for (Boolean chunk : chunks) {
            btn_online2.setEnabled(chunk);
        }
    }
};
worker.execute();

CodePudding user response：

I was able to resolve using the following method in the initialize() of the frame.

Adding that change part of the swingworker allowed the button to check the flag and assign it to itself whenever it changes.

Now whenever the internet is disconnected the button is disabled and whenever connected the button is enabled.

SwingWorker<Void, String>  worker = new SwingWorker<Void, String>()
        {
            public Void doInBackground()
            {
                while(true)
                {
                    
                    try {
                        isConnectedToInternet = Utils.isConnectedToInternet();
                        if (isConnectedToInternet) {
                            btn_online2.setEnabled(isConnectedToInternet);
                        } else {
                            btn_online2.setEnabled(isConnectedToInternet);
                        }
                        logger.debug("Internet connection status: "   isConnectedToInternet);
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        worker.execute();