在jframe上动态切换图像

Question

我有一个创建GUI的任务，当选择菜单项时（例如文件，新图片）切换图像，并且还包含用于放大和缩小图像的按钮。当我尝试使用我的代码切换图像时，图像仅部分加载。当我最小化窗口然后重新打开它时，图像被完全加载。我想知道为什么会这样。

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import java.io.*;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;

public class ImageZoom extends JPanel {

 private Image image;
 int x, y;
 private JButton zoomIn;
 private JButton zoomOut;
 private JMenuBar bar;
 private JMenu file;
 private JMenuItem choosePic = new JMenuItem("New Picture");
 private String pics[] = {"waterfall.jpg", "mountains.jpg"};
 private int picIndex = 1;
 int imageHeight = getHeight();
 int imageWidth = getWidth();
 int zoom = 1;
 Image images[] = new Image[2];

 public ImageZoom() {

  try {
   images[0] = ImageIO.read(new File("waterfall.jpg"));
   images[1] = ImageIO.read(new File("mountains.jpg"));
  } catch (IOException e) {}

  zoomIn = new JButton("+");
  zoomOut = new JButton("-");

 JPanel panel = new JPanel();
 bar = new JMenuBar();
 file = new JMenu("File");  
 file.add(choosePic);
 bar.add(file);

 choosePic.addActionListener (new ActionListener() {

   public void actionPerformed (ActionEvent e) {

    if (e.getSource() == choosePic) {

     repaint();

    }

   }
  }); 

  zoomIn.addActionListener (new ActionListener() {

   public void actionPerformed (ActionEvent e) {

    if (e.getSource() == zoomIn) {     

      if (zoom < 6) {
      zoom += 1;
      repaint();

     }

    }

   }

  });


  zoomOut.addActionListener( new ActionListener() {

   public void actionPerformed (ActionEvent e) {

    if (e.getSource() == zoomOut) {    

     if (zoom > 1) {
     zoom -= 1;
     repaint();

     }

    }     

   }

  });  

 }

 public JPanel getButtonPanel () {

  JPanel panel = new JPanel();
  panel.add(zoomIn);
  panel.add(zoomOut);

  return panel;

 }

 public Image getImage() {

  try {
  image = ImageIO.read(new File(pics[picIndex % 2]));
  picIndex++;

  }
  catch (IOException e){}
  return image;

 }

 protected void paintComponent (Graphics g) {

  imageHeight = getHeight() * zoom;
  imageWidth = getWidth() * zoom;

  super.paintComponent(g);
  g.drawImage(getImage(), 0, 0, imageWidth, imageHeight, null);

 }

 public void createJFrame () {

 JFrame frame = new JFrame(); 

 ImageZoom imgZoom = new ImageZoom();

 frame.setJMenuBar(bar);  
 frame.add(imgZoom);
 frame.add(getButtonPanel(), BorderLayout.SOUTH);

 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 frame.setSize(650, 650); 
 frame.setResizable(false);
 frame.setVisible(true); 

 }

}

class Test {

 public static void main (String[] args) {

 ImageZoom zoom = new ImageZoom();
 zoom.createJFrame();

 } 

}

Answer 1

为简单起见，您应该使用JLabel并调用其setIcon方法来切换图像。您可以根据需要动态缩放图像（只保留对原始图像的引用）

问题＃1

您应该将this传递给drawImage，这将允许该组件充当ImageObserver，并根据图像状态中的事件根据需要安排其他重印，从而导致

问题＃2

您不应该在getImage方法中调用paintComponent，paintComponent可能会因为多种原因而被调用，其中许多原因是您无法控制甚至不知道的paintComponent应该只绘制组件的当前状态，永远不要尝试更改状态

旁注：不要反复尝试加载图片，最好加载一次并继续重复使用已加载的参考