JScrollPane與JPanel 捲軸 解決canvas的捲軸問題

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當用JScrollPane和JPanel顯示圖片時，需要將JPanel的PrefferedSize及時傳遞給JScrollPane，否則容易出現JScrollPane的捲軸無法與圖片大小匹配的問題，下面是從Matrix網上搜到的一段代碼供參考使用：

 

import java.awt.Dimension;import java.awt.Graphics;import java.awt.Image;import java.awt.event.MouseEvent;import java.awt.event.MouseListener;import javax.swing.ImageIcon;import javax.swing.JFrame;import javax.swing.JPanel;import javax.swing.JScrollPane;public class ScrollPaneDemo extends JFrame implements MouseListener {        ImagePanel jp;        JScrollPane jsp;        public ScrollPaneDemo() {                super("JScrollPane Demo");                jp = new ImagePanel();                jp.setPreferredSize(new Dimension(600, 400));                jsp = new JScrollPane(jp);                jp.addMouseListener(this);                getContentPane().add(jsp);                setSize(640, 480);                setDefaultCloseOperation(EXIT_ON_CLOSE);                setVisible(true);        }        public void mouseClicked(MouseEvent e) {                System.out.println("mouseClicked");                jp.enlarge();                jp.setPreferredSize(jp.getPreferredSize());                jsp.validate();        }        public void mousePressed(MouseEvent e) {                // System.out.println("mousePressed");        }        public void mouseReleased(MouseEvent e) {                // System.out.println("mouseReleased");        }        public void mouseEntered(MouseEvent e) {                // System.out.println("mouseEntered");        }        public void mouseExited(MouseEvent e) {                // System.out.println("mouseExited");        }        public static void main(String[] args) {                new ScrollPaneDemo();        }}class ImagePanel extends JPanel {        private Image image;        private Dimension theSize = new Dimension(600, 400);        public void setImage(Image image) {                this.image = image;                this.repaint();        }        public Image getImage() {                return this.image;        }        public void paintComponent(Graphics g) {                ImageIcon img = new ImageIcon("Winter.jpg");                g.drawImage(img.getImage(), 0, 0, theSize.width, theSize.height, null);        }        public void enlarge() {                theSize.width = (theSize.width * 101) / 100;                theSize.height = (theSize.height * 101) / 100;                setSize(theSize);        }                public Dimension getPreferredSize() {                return this.theSize;        }}

因為scrollPane是根據裡面的子控制項的preferredSize來確定捲軸的。
所以圖片變化而捲軸無響應的問題在於讓image尺寸變化時，scrollPane能得到新的資料。

解決方式有兩種，一種是改變大小時重新設定JPanel的preferred size；
一種是重載getPreferredSize()方法，按照需要返回，樓主的情況可以返回當前
圖片的大小的Dimension。

文章出自：http://xu.wy.blog.163.com/blog/static/11568296200786103315608/