如何使用JScrollBar缩放图像？

Question

我想使用JScrollBar来放大和缩小图像，但它不起作用。我的代码出了什么问题？

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

 public class piczoominandout extends JFrame
{
  public JScrollBar scroll;
  public JLabel lbl;
  public Image image;
  public int x, y, width, height;

  public piczoominandout()
 {
   super("picture zoom");
   Toolkit toolkit = Toolkit.getDefaultToolkit();
   image = toolkit.getImage("Snake.jpg");
   Container c = getContentPane();
   ImagePanel imagePane = new ImagePanel(image);

   c.setLayout(new BorderLayout());
   lbl = new JLabel("0");
   c.add(lbl, BorderLayout.SOUTH);
   scroll = new JScrollBar(
           JScrollBar.HORIZONTAL,50,10,0,100);
   scroll.addAdjustmentListener(new AdjustmentListener() {
     public void adjustmentValueChanged(
                         AdjustmentEvent evt) {
        JScrollBar s = (JScrollBar)evt.getSource();
        if ( !s.getValueIsAdjusting() ) {
           int v = (int)s.getValue();
           width +=v;
           height +=v;

           repaint();
           lbl.setText(Integer.toString(v));
        }
     } });
    c.add(imagePane,BorderLayout.CENTER );

    c.add(scroll, BorderLayout.NORTH);
 }
 class ImagePanel extends JPanel
 {
  public ImagePanel(Image img) { image = img;}
  public void paintComponent(Graphics g)
  {
   Insets ins = getInsets();
   super.paintComponent(g);
   width = image.getWidth(this);
   height = image.getHeight(this);
   x = ins.left+5; y = ins.top+5;
   g.drawImage(image,x,y,width,height,this);
  }
 }

  public static void main(String[] args)
  {
   SwingUtilities.invokeLater(new Runnable() {
     public void run()
     {
      piczoominandout frame = new piczoominandout();
      frame.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
      frame.setSize(600,300);
      frame.setVisible(true);

       }
     });
  }

}

Answer 1

你的代码中有很多错误。它需要全面的重新思考。

我只给你一些基本的提示：

当你使用一个不设置监听器的ImagePanel构造器时(注意NullPointerException);

• You're没有缩放图像-在paintComponent上你只是按原样绘制图像；

• 你在监听器滚动值中添加width和height，并且你试图在paintComponent中重置它们-这不是你应该做的。提示:有一个Graphics类的方法:必须在EDT:

上创建和更改g.drawImage(image, x, y, width, height, this);;

• Every Swing组件

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            JFrame frame = new JFrame();
            //etc.
        }
    });
}