不断变化的JLabel背景颜色

Question

I'm new to GUI programming and I tried out some code and wanted to constantly change the background of a JPanel called "HeaderPanel".

Why isnt this working as I wished? (Color stays the same...)

private void changeColors() {
    int r = 0;
    int g = 155;
    int b = 12;

    while(true) {
        r = (r+1)%255;
        g = (g+1)%255;
        b = (b+1)%255;

        Color color = new Color(r,g,b);
        HeaderPanel.setBackground(color);
    }
}

Answer 1

Your while loop is stopping the repaint manager from ever getting around to changing the colors.

You need to, some how, execute the request in the background, something like this

public class TestLabel extends JLabel {

    private Timer timer;

    private int r = 0;
    private int g = 155;
    private int b = 12;

    public TestLabel() {

        setText("Hello world");
        setOpaque(true);

        timer = new Timer(1000, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                System.out.println("tick");

                r = (r + 1) % 255;
                g = (g + 1) % 255;
                b = (b + 1) % 255;

                Color color = new Color(r, g, b);
                setBackground(color);

                System.out.println(color);

                if (r == 0 && b == 0 && g == 0) {

                    r = 0;
                    g = 155;
                    b = 12;

                }

                invalidate();
                revalidate();
                repaint();

            }
        });

        timer.setRepeats(true);
        timer.setCoalesce(true);
        timer.start();

    }
}

You might like to read up on

• The Event Dispatching Thread
• Concurrency in Swing

UPDATED with Extended Example

public class TestLabel extends JLabel {

    private Timer timer;

    private Object[][] colors = {{"Black", Color.BLACK},
        {"Blue", Color.BLUE},
        {"Cyan", Color.CYAN},
        {"Dark Gray", Color.DARK_GRAY},
        {"Gray", Color.GRAY},
        {"Green", Color.GREEN},
        {"Light Gary", Color.LIGHT_GRAY},
        {"Mangenta", Color.MAGENTA},
        {"Orange", Color.ORANGE},
        {"Pink", Color.PINK},
        {"Red", Color.RED},
        {"White", Color.WHITE},
        {"Yellow", Color.YELLOW}};

    public TestLabel() {

        setText("Hello world");
        setOpaque(true);

        timer = new Timer(1000, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                System.out.println("tick");

                int index = (int) Math.round((colors.length - 1) * Math.random());

                Object[] group = colors[index];

                setBackground((Color)group[1]);
                setText((String)group[0]);

            }
        });

        timer.setInitialDelay(0);
        timer.setRepeats(true);
        timer.setCoalesce(true);
        timer.start();

    }
}

Answer 2

I'm not a swing developer, but don't you have to "repaint" or something like that when you change the color property? In the other hand, you will need another thread to keep updating the colors.

Summarizing

• A code to change the panel background color (include repaint)
• A thread to invoke the above code.

Answer 3

你需要告诉你的JPanel自己绘画，可能是通过调用invalidate() 。