java - 如何让一个越来越透明最后消失的JPanel呢？

Question

我想制作一个扩展 JPanel 的面板，当它可见时，它开始变得越来越透明，最后消失。我的代码有什么问题？

public class BaloonPanel extends JPanel
{

private float transparency = 1f;
Timer timer;

public BaloonPanel()
{

    setBackground(Color.white);
    ActionListener action = new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent e)
        {
            transparency = transparency - 0.01f;

            if (transparency < 0.0f)
            {
                timer.stop();
            }
            repaint();
        }
    };

    timer = new Timer(100, action);
    timer.start();
}

@Override
public void paint(Graphics g)
{
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, transparency));
    super.paint(g2);
    g2.dispose();
}

Answer 1

因为 BallonPanel 是不透明的，所以重绘管理器懒得在它下面进行绘制。这是对油漆工艺的优化，不需要油漆的东西为什么要油漆。

您需要“说服”重绘管理器在您的组件下方进行绘制，同时仍然绘制其背景。

将 BallonPanel 设置为透明 (setOpaque(false)) 并更新 paint 方法以填充背景。

public class FadePane {

    public static void main(String[] args) {
        new FadePane();
    }

    public FadePane() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.getContentPane().setBackground(Color.BLUE);
                frame.setBackground(Color.BLUE);
                frame.add(new BaloonPanel());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

            }
        });
    }

    public class BaloonPanel extends JPanel {

        private float transparency = 1f;
        Timer timer;

        public BaloonPanel() {

            setBackground(Color.white);
            ActionListener action = new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    transparency = transparency - 0.1f;

                    if (transparency < 0.1f) {
                        transparency = 0;
                        timer.stop();
                    }
                    invalidate();
                    repaint();
                }
            };

            timer = new Timer(100, action);
            timer.setRepeats(true);

            setOpaque(false);

            final JButton fade = new JButton("Fade");
            fade.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    timer.start();
                    fade.setEnabled(false);
                }
            });

            setLayout(new GridBagLayout());
            add(fade);
        }

        @Override
        public void paint(Graphics g) {
            Graphics2D g2 = (Graphics2D) g.create();
            System.out.println(transparency);
            g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, transparency));
            g2.setColor(getBackground());
            g2.fillRect(0, 0, getWidth(), getHeight());
            super.paint(g2);
            g2.dispose();
        }
    }
}