JScrollPane与JPanel 滚动条 解决canvas的滚动条问题

当用JScrollPane和JPanel显示图片时，需要将JPanel的PrefferedSize及时传递给JScrollPane，否则容易出现JScrollPane的滚动条无法与图片大小匹配的问题，下面是从Matrix网上搜到的一段代码供参考使用：

 

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;

        }

}

因为scrollPane是根据里面的子控件的preferredSize来确定滚动条的。
所以图片变化而滚动条无响应的问题在于让image尺寸变化时，scrollPane能得到新的数据。

解决方式有两种，一种是改变大小时重新设置JPanel的preferred size；
一种是重载getPreferredSize()方法，按照需要返回，楼主的情况可以返回当前
图片的大小的Dimension。

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