同时调整 JPanel 大小时调整图像大小

debugcn 发表于 Dev

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我的代码的问题是我的图像只能获得JFrame- 但我希望每次用户更改窗口大小时它都会更改大小。

图像大小也应该相对于JFrame大小还是它的JPanel？如果是这样，我将如何实现这一目标？

这是我的代码：

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

public class MainFrame extends JFrame {

private JPanel card1;
private JPanel principalPanel,centerPanel;
private BufferedImage image;

public MainFrame() {

    setSize(800,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);

    URL url = null;
    try {
        url = new URL("https://i.stack.imgur.com/7bI1Y.jpg");
    } catch (MalformedURLException e) {

    }
    try {
        image = ImageIO.read(url);
    } catch (IOException e) {
        System.out.println("Can not find image");
    }


    Image scaledImage = image.getScaledInstance(this.getWidth(),
            this.getHeight(),Image.SCALE_SMOOTH);

    card1 = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawImage(scaledImage,0,0,this);
        }
    };

    centerPanel = new JPanel();
    centerPanel.setLayout(new CardLayout());
    centerPanel.add(card1,"1");

    principalPanel = new JPanel();
    principalPanel.setLayout(new BorderLayout());
    principalPanel.add(centerPanel,BorderLayout.CENTER);

    setContentPane(principalPanel);
}

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new MainFrame();
        }
    });
}
}

安德鲁·汤普森

图像可以（确实应该）在paintComponent(Graphics)方法中缩放。这样它就可以更改为面板的任何尺寸。

另请参阅代码中的注释：

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.net.URL;

public class MainFrame2 extends JFrame {

    private JPanel card1;
    private BufferedImage image;

    public MainFrame2() {

        setSize(800, 600);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        try {
            // if there is a problem with URL - no point trying to load
            URL url = new URL("https://i.stack.imgur.com/7bI1Y.jpg");
            image = ImageIO.read(url);
        } catch (Exception e) {
            System.out.println("Problem loading image");
            e.printStackTrace();
        }

        /* The frame will actually be larger than the panel. 
        Better to scale the image to the SIZE OF THE PANEL ...
        Image scaledImage = image.getScaledInstance(this.getWidth(),
                this.getHeight(), Image.SCALE_SMOOTH); */

        card1 = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                // .. this is how.
                g.drawImage(image, 0, 0, getWidth(), getHeight(), this);
            }
        };

        setContentPane(card1);

        setVisible(true); // this should be last! 
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new MainFrame2();
            }
        });
    }
}

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