JProgressBar 复制

Question

在我将 JFrame GlassPane 设置为可见之前，我的 JProgressBar 运行良好。然后它随机决定在屏幕上拍摄并复制。

这是一个显示错误的动画 GIF。无论我的代码是什么，都会发生这种情况——即使是非常基本的 GUI

http://i.gyazo.com/bd70df610a3cad6bfff258b80f21c78a.gif

只有当我这样做时才会发生这种情况 this.getGlassPane().setVisible(true);

代码如下：

    public void setProgress(final int percent) {
            pb.setValue(percent);

            if (percent == 100) {

                    SwingUtilities.invokeLater(new Runnable() {
                            public void run() {
                                    FadingMirror glassPane = new FadingMirror();
                                    instance.setGlassPane(glassPane);

                                    ((FadingMirror)instance.getGlassPane()).startAnimation();
                                    ((FadingMirror)instance.getGlassPane()).setVisible(true);
                            }
                    });
            }
    }

    @Override
    public void addText(String text) {
            System.out.println(text);
    }

    public static class FadingMirror extends JPanel implements ActionListener {

            /**
             *
             */
            private static final long serialVersionUID = 7341931028635559650L;
            private float opacity = 0f;
            private Timer fadeTimer;

            public void startAnimation() {
                    fadeTimer = new javax.swing.Timer(75, this);
                    fadeTimer.setInitialDelay(0);
                    fadeTimer.start();

            }

            public void actionPerformed(ActionEvent e) {
                    opacity += .03;
                    if(opacity > 1) {
                            opacity = 1;
                            fadeTimer.stop();
                            fadeTimer = null;
                    }
                    repaint();
            }

            public void paintComponent(Graphics g) {
                    //super.paintComponent(g); //Cannot do this before setting composite without destroying the animation
                    ((Graphics2D) g).setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
                    g.setColor(getBackground());
                    g.fillRect(0,0,getWidth(),getHeight());
            }
    }

}

感谢阅读

Answer 1

制作 Graphics 对象的副本，在 that 上设置合成并用它进行绘制。然后丢弃它。

public void paintComponent(Graphics g) {
    super.paintComponent(g); 
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
    g2.setColor(getBackground());
    g2.fillRect(0,0,getWidth(),getHeight());
    g2.dispose();
}

Answer 2

Graphics 是共享资源。通常，框架绘制的任何 Swing 组件都使用相同的Graphics 上下文。 paintComponent 的工作之一是准备 Graphics 用于绘画的上下文，通常通过填充当前背景颜色。

因为Graphics 是共享资源，所以您对它所做的任何更改都会影响在它之后绘制的任何其他组件。您应该将Graphics 上下文恢复到paintComponent 存在之前的状态。这很容易通过使用Graphics#create 来实现，它将创建Graphics 上下文属性的快照，但不会影响原始文件。然后，您应该确保在完成后在您的副本上调用Graphics#dispose。

您的玻璃板也应该是透明的，允许在其下方涂漆。

import java.awt.AlphaComposite;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRootPane;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;

public class Test {

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

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setGlassPane(new FadePane());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class FadePane extends JPanel {

        private float alpha = 0;
        private Timer timer;

        public FadePane() {
            timer = new Timer(40, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    alpha += 0.1f;
                    if (alpha > 1.0) {
                        alpha = 1f;
                        timer.stop();
                    }
                    repaint();
                }
            });
            setOpaque(false);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setComposite(AlphaComposite.SrcOver.derive(alpha));
            g2d.setColor(getBackground());
            g2d.fillRect(0, 0, getWidth(), getHeight());
            g2d.dispose();
        }

        public void fadeAway() {
            setVisible(true);
            timer.stop();
            alpha = 0f;
            timer.start();
        }

    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            setBorder(new EmptyBorder(50, 50, 50, 50));

            JButton btn = new JButton("It's better to burn out then fade away");
            btn.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    JRootPane rootPane = (JRootPane) SwingUtilities.getAncestorOfClass(JRootPane.class, TestPane.this);
                    FadePane fadePane = (FadePane) rootPane.getGlassPane();
                    fadePane.fadeAway();
                }
            });
            add(btn);
        }

    }

}