java - 如何复制缓冲图像

Question

我编写了以下示例来解决我遇到的问题。当您按下按钮时，controlWhichImage 会切换到 2。问题是，当它从原始图像切换到副本时，图像会消失。

public class PainterDemo01 extends JPanel implements ActionListener {
    BufferedImage createdImage;
    BufferedImage img;
    int controlWhichImage;
    JFrame mainFrame;
    JButton changePicture;

    public PainterDemo01(){
        changePicture = new JButton("Press");
        changePicture.addActionListener(this);
        controlWhichImage = 1;
        mainFrame = new JFrame();
        mainFrame.add(this);
        this.add(changePicture);
        mainFrame.setPreferredSize(new Dimension(600,600));
        mainFrame.setVisible(true);
        mainFrame.pack();
       img = loadImage();       
    }

    public BufferedImage loadImage(){
        img = null;
        try {
            img = ImageIO.read(new File("/home/gerry/Desktop/100_0647.JPG"));
        } catch (IOException e){
            System.out.println("no file here");
        }
        return img;
    }

    @Override
    protected void paintComponent(Graphics g){
        super.paintComponent(g);        

      loadImage();  
        if (createdImage == null){
            this.createdImage = new BufferedImage(this.getWidth(),this.getHeight(), BufferedImage.TYPE_INT_ARGB);
        }

        Graphics g2 = this.createdImage.getGraphics();      

        if (controlWhichImage == 1){
                g2.drawImage(img,0,0,img.getWidth(),img.getHeight(),null);
                g.drawImage(img, 0,0,img.getWidth(),img.getHeight(),null);       
                g2.dispose();
            }
        if (controlWhichImage == 2){
                //Draw bufferedImage on to to JPanel
                g.drawImage(this.createdImage,this.createdImage.getWidth(),this.createdImage.getHeight(),null);
        }               
    }
    @Override
    public void actionPerformed(ActionEvent e){
        controlWhichImage = 2;
        repaint();
    }

    public static void main(String[] args) {
        // TODO code application logic here
             java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new PainterDemo01().setVisible(true);
            }
        });
    }    
}

Answer 1

问题是 getGraphics (或者更好的名称 createGraphics)在 if 语句之外被调用，同样对于 2，因此两者都会导致资源泄漏(因为没有调用 g2.dispose)，并且也是一个干净的状态。

    if (controlWhichImage == 1) {
        Graphics g2 = createdImage.getGraphics();      
        g2.drawImage(img,0,0,img.getWidth(),img.getHeight(),null);
        g2.dispose();
    }

还可以执行诸如在绘制代码之外加载图像之类的操作。