JPanel does not show until after the code

Question

What I want to do is to show a new panel with a progress bar while the process takes place.

My code is as follows:

case "GoButton":
    cards.show(this, "pp");
    this.test();
    cards.show(this, "panel1");
    break;

That is in a actionPerformed method

but when I run the program it just ignores the first cards.show, it executes the test code and then it executes the second cards.show

I also provide you the rest of the code in case you need it

public CreatePanel(JFrame frame) {
        ext = new ArrayList<>();
        files = new ArrayList<>();

        this.mainWindow = frame;
        this.setSize(256, 256);
        cards = new CardLayout();
        this.setLayout(cards);

        panel1 = new JPanel(null);
        createPanel1(panel1);
        this.add(panel1, "panel1");

        panel2 = new JPanel(null);
        createPanel2(panel2);
        this.add(panel2, "panel2");

        panel3 = new JPanel(null);
        createPanel3(panel3);
        this.add(panel3, "pp");

        cards.show(this, "panel1");
    }

public class ProgressPanel {
    private static JPanel panel;
    private static JProgressBar progressBar;
    private static int progress;

    public static JPanel createProgressPanel(){
        ProgressPanel.panel = new JPanel(null);
        ProgressPanel.initPanel();
        return ProgressPanel.panel;
    }

    private static void initPanel(){
        panel.setLayout(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();

        progressBar = new JProgressBar(0, 100);
        progressBar.setValue(progress);
        progressBar.setStringPainted(true);
        panel.add(progressBar, c);
    }

    public static void updateProgress(int x){
        ProgressPanel.progress += x;
    }

    public void resetProgress(){
        this.progress = 0;
    }
}

`panel3 = new JPanel(null);` Java GUIs have to work on different OS', screen size, screen resolution etc. using different PLAFs in different locales. As such, they are not conducive to pixel perfect layout. Instead use layout managers, or [combinations of them](http://stackoverflow.com/a/5630271/418556) along with layout padding and borders for [white space](http://stackoverflow.com/a/17874718/418556). — Andrew Thompson, May 05 '15 at 23:38

Hovercraft Full Of Eels · Accepted Answer · 2015-05-05T22:49:21.367

Your problem likely likes here: this.test();. I'm betting that this method calls long running code, and since it's being called on the Swing event thread, it's tying up this thread preventing your GUI from updating itself and in fact completely freezing the GUI. Solution: use a SwingWorker or other background thread for long-running tasks. Please have a look at Concurrency in Swing.

Note that if you do use a SwingWorker, you'll need to use either a PropertyChangeListener or the done() method to be notified when the background thread has completed and that it's time to call cards.show(this, "panel1");. Myself, I'd add a PropertyChangeListener to my SwingWorker, since this way, I could both listen for the completion of the listener, and also could listen for changes in the worker's progress property, and then use that value to set my JProgressBar's value.

Hmm i will look into it and i will apply the changes tomorrow to let you know. Thanks for the quick reply! — Angelo Uknown, May 05 '15 at 23:10

JPanel does not show until after the code

1 Answers1