在JScrollPane中按比例绘制图像

Question

我有一个加载图像滚动窗格。我将这个图像与她的自然大小，如果这个图像太大，我将不会激活滚动条，但这个指令

  g.drawImage(immagine, 0, 0, getWidth(), getHeight(), this); 

用于放置在滚动窗格中的缩放图像。我能做什么？

类GUI：

    import java.awt.*;
    import java.awt.event.*;
    import java.io.File;
    import javax.swing.*;

    public class Gui implements ActionListener {

        private JFrame frmEditor;

        private Mappa content;
        private JMenuItem mntmSfondo;
        private JScrollPane scrollabile;

        /**
         * Launch the application.
         */
        public static void main(String[] args) {
            EventQueue.invokeLater(new Runnable() {
                public void run() {
                    try {
                        Gui window = new Gui();
                        window.frmEditor.setVisible(true);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }

        /**
         * Create the application.
         */
        public Gui() {
            initialize();
        }

        /**
         * Initialize the contents of the frame.
         */
        private void initialize() {
            frmEditor = new JFrame();
            frmEditor.setFont(UIManager.getFont("TextArea.font"));
            frmEditor.setBounds(50, 50, 1024, 768);
            frmEditor.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frmEditor.getContentPane().setLayout(new BorderLayout(0, 0));

            JPanel panelTile = new JPanel();
            panelTile.setLayout(new BorderLayout(0, 0));

            content = new Mappa(null);
            content.setMinimumSize(new Dimension(150, 150));
            scrollabile = new JScrollPane(content);
            frmEditor.getContentPane().add(scrollabile, BorderLayout.CENTER);

            inizializzaMenu();
        }

        /**
         * Initialize the menu.
         */
        private void inizializzaMenu() {

            JMenuBar menuBar = new JMenuBar();
            frmEditor.setJMenuBar(menuBar);

            JMenu mnAltro = new JMenu("Modify");
            menuBar.add(mnAltro);

            mntmSfondo = new JMenuItem("Load Background");
            mntmSfondo.addActionListener(this);
            mnAltro.add(mntmSfondo);
        }

        public void actionPerformed(ActionEvent e) {
            Object source = e.getSource();
            if (source == mntmSfondo) {
                JFileChooser fc = new JFileChooser("tuttiSfondi");
                int result = fc.showOpenDialog(null);
                if (result == JFileChooser.APPROVE_OPTION) {
                    File file = fc.getSelectedFile();
                    try {
                        content.setImage(file);
                        //content = new Mappa(file);
                        //scrollabile.setViewportView(content);
                    } catch (Exception ex) {
                    }
                }
                if (result == JFileChooser.CANCEL_OPTION) {
                }
            }
        }

    }

类映射：

    import java.awt.*;
    import java.awt.image.BufferedImage;
    import java.io.*;

    import javax.imageio.ImageIO;
    import javax.swing.*;

    public class Mappa extends JPanel {

        BufferedImage immagine;

        public Mappa(File fileImmagine) {

            if (fileImmagine != null ) {

                BufferedImage img = null;
                try {
                    img = ImageIO.read(new File(fileImmagine.getPath()));
                } catch (IOException e) {
                    e.printStackTrace();
                }
                this.immagine = img;
            }
            repaint();
        }

        public void setImage(File file) throws IOException {

            this.immagine = ImageIO.read(file);
            String name = file.getPath();
            System.out.println(name);
            repaint();

        }

        public void paintComponent(Graphics g) {

            super.paintComponent(g);
            g.clearRect(0, 0, 4000, 4000);
            g.drawImage(this.immagine, 0, 0, getWidth(), getHeight(), this);

            System.out.println("Called Repaint() on Mappa");

        }
    }

Answer 1

我将这个图像与她的自然大小，如果这个图像太大，我将不会激活滚动条，

使用JLabel包含图像并将其包装在JScrollPane中应该可以轻松实现您想要的目标。从以下示例中获得提示：

class AFrame extends JFrame
{
   public AFrame()
  {

     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     setTitle("Image view Demo with JScrollPane");

     ImageIcon image = new ImageIcon("myImage.png"); // pass the file location of an image
     JLabel label = new JLabel(image);
     JScrollPane scrollPane = new JScrollPane(label);
     scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
     scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
     add(scrollPane, BorderLayout.CENTER);
     pack();
  }

 public static void main(String[] args)
 {
    SwingUtilities.invokeLater(new Runnable() {

       @Override
       public void run() {
          new AFrame().setVisible(true);
       }
    });

  }
}

Answer 2

JScrollPane或者更确切地说，JViewPort将使用组件（在本例中是“视图”）的首选大小作为确定视图应该有多大的基础。

当视图扩展到滚动窗格的大小之外时，它将显示滚动条。

因此，基本上，您需要重写公共类Mappa extends JPanel{面板的GetPreferredSize，例如

public class Mappa extends JPanel {
    //...
    public Dimension getPreferredSize() {
        return immagine == null ? new Dimension(200, 200) : new Dimension(immagine.getWidth(), immagine.getHeight());
    }
    //...
}

这将鼓励jviewport始终与图像大小相同。

还有两件事...

首先，你不应该依赖神奇的数字，例如

g.clearRect(0, 0, 4000, 4000);

应该更像是...

g.clearRect(0, 0, getWidth(), getHeight());

其次,

super.paintComponent(g);

任何方式都可以做到这一点，所以调用clearrect是没有意义的...

您可能还想看看scrollable，但这是一个相当高级的主题