如何正确使用repaint()和revalidate()？

Question

我是 JPanel 的新手，不太了解如何重置它。一旦选择了图片并且用户想要 select 一张新图片，我希望它擦除旧的 selected 图片并粘贴新图片。但我不确定如何。我见过repaint()和revalidate()用过，但我显然不知道怎么用。那么我该如何实现呢？

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JRadioButtonMenuItem;

public class Menu extends JFrame {
    JMenuBar menuBar;
    ButtonGroup pictureGroup, problemsGroup;
    BufferedImage picture1img, picture2img, picture3img;
    JMenu choiceOfThreePictures, numberOfProblems;
    JRadioButtonMenuItem picture1, picture2, picture3, fourProblems, nineProblems, sixteenProblems;
    // /Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture1.jpg
    // /Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture2.png
    // /Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture3.jpg

    public Menu() {
        // Create the menu bar.
        menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        // Create Picture choices on Menu Bar
        choiceOfThreePictures = new JMenu("Picture Choices");
        // Add Picture choices on Menu Bar
        menuBar.add(choiceOfThreePictures);
        // Create MenuItems onto Picture choices
        pictureGroup = new ButtonGroup();
        picture1 = new JRadioButtonMenuItem("Picture 1");
        picture2 = new JRadioButtonMenuItem("Picture 2");
        picture3 = new JRadioButtonMenuItem("Picture 3");
        // Add Picture Choices to Picutre choices menu
        choiceOfThreePictures.add(picture1);
        pictureGroup.add(picture1);
        choiceOfThreePictures.add(picture2);
        pictureGroup.add(picture2);
        choiceOfThreePictures.add(picture3);
        pictureGroup.add(picture3);

        // Create Number Of Problems on Menu Bar
        numberOfProblems = new JMenu("Number Of Problems");
        // Add Number Of problems on Menu Bar
        menuBar.add(numberOfProblems);
        // Create Menu Items onto Number Of problems
        problemsGroup = new ButtonGroup();
        fourProblems = new JRadioButtonMenuItem("4");
        nineProblems = new JRadioButtonMenuItem("9");
        sixteenProblems = new JRadioButtonMenuItem("16");
        // Add Number Of problems onto menu
        numberOfProblems.add(fourProblems);
        problemsGroup.add(fourProblems);
        numberOfProblems.add(nineProblems);
        problemsGroup.add(nineProblems);
        numberOfProblems.add(sixteenProblems);
        problemsGroup.add(sixteenProblems);

        // Start creating ActionListeners
        picture1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("Working");
                try {
                    picture1img = ImageIO.read(new File("/Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture1.jpg"));
                    getContentPane().add(new JLabel(new ImageIcon(picture1img)));
                    revalidate();
                    repaint();
                    setVisible(true);

                } catch (IOException e) {
                    System.out.println("Couldn't find image.");
                }
            }
        });
        picture2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("Working");
                try {
                    picture2img = ImageIO.read(new File("/Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture2.jpg"));
                    getContentPane().add(new JLabel(new ImageIcon(picture2img)));
                    revalidate();
                    repaint();
                    setVisible(true);
                } catch (IOException e) {
                    System.out.println("Couldn't find image.");
                }
            }
        });
        picture3.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("Working");
                try {
                    picture3img = ImageIO.read(new File("/Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture3.jpg"));
                    getContentPane().add(new JLabel(new ImageIcon(picture3img)));
                    revalidate();
                    repaint();
                    setVisible(true);

                } catch (IOException e) {
                    System.out.println("Couldn't find image.");
                }
            }
        });
    }

    public static void main(String[] args) {
        Menu mb = new Menu();
        mb.setSize(900, 700);
        mb.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mb.setVisible(true);
    }
}

Answer 1

您使用得很好，您甚至可以远程 repaint() 调用，因为重新验证已经足够了。问题是，您正在 添加新图像 但您 没有从 contentPane 中删除以前添加的图像 这就是为什么不切换。

所以如果你这样做

                    picture3img = ImageIO.read(new File("/Users/Administrator/Dropbox/Java/HW6Wilson/HW6Wilson/Picture3.jpg"));
                    getContentPane().removeAll(); // HERE IS IMPORTANT PART
                    getContentPane().add(new JLabel(new ImageIcon(picture3img)));
                    revalidate();

它会起作用

更好的方法是将单个标签作为 "image display" 并在 JLabel 上使用 setIcon(icon) 而不是更改整个标签。

如何正确使用repaint()和revalidate()？

How to correctly use repaint() and revalidate()?

java

jpanel