如何停止组件适应 JScrollPane 内的 JPanel 的大小

Question

当空间不足时，JPanel（具有 BoxLayout）内的组件会调整大小。

JPanel 位于 JScrollPane 内部，但由于组件被调整大小，滚动条是无用的。

顺便说一下，JScrollPane 也是 JTabbedPane 中的内容。

为每个组件设置最小尺寸和首选尺寸并不能解决问题：

this.setPreferredSize(new Dimension(100,20));
this.setMinimumSize(new Dimension(100,20));

知道如何处理这个问题吗？

问题截图：

这就是我不希望它看起来像，具有固定大小：

Answer 1

我获取了图像中可见的信息，并创建了一个示例 Swing GUI 来显示相同的信息。

我不知道我的代码与您的代码有何不同。 我在下载的JPanel中放置了一个JLabel和两个JTextAreas 。 我创建了一个主JPanel来保存下载JPanels 。

这是我使用的完整的可运行代码。 我将附加类设为内部类，这样我就可以将代码作为一个块发布。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;

import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class MusicDownloadGUI implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new MusicDownloadGUI());
    }
    
    private final MusicDownloadModel model;
    
    public MusicDownloadGUI() {
        this.model = new MusicDownloadModel();
    }

    @Override
    public void run() {
        JFrame frame = new JFrame("Music Download");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        frame.add(createMainPanel(), BorderLayout.CENTER);
        
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
    
    private JScrollPane createMainPanel() {
        JPanel panel = new JPanel(new GridLayout(0, 1, 5, 5));
        panel.setBackground(Color.WHITE);
        panel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        
        for (Track track : model.getDownloads()) {
            panel.add(createDownloadPanel(track));
        }
        
        JScrollPane scrollPane = new JScrollPane(panel);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        return scrollPane;
    }
    
    private JPanel createDownloadPanel(Track track) {
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT, 10, 10));
        panel.setBackground(Color.WHITE);
        
        JLabel label = new JLabel(new ImageIcon(track.getAlbumCover()));
        panel.add(label);
        
        JTextArea titleArea = new JTextArea(3, 30);
        titleArea.setEditable(false);
        titleArea.setText(createTitleArea(track));
        panel.add(titleArea);
        
        JTextArea artistArea = new JTextArea(3, 25);
        artistArea.setEditable(false);
        artistArea.setText(createArtistArea(track));
        panel.add(artistArea);
        
        return panel;
    }
    
    private String createTitleArea(Track track) {
        StringBuilder builder = new StringBuilder();
        builder.append(track.getTitle());
        builder.append(System.lineSeparator());
        builder.append("Download -- ");
        builder.append(track.getPercentDownloaded());
        builder.append("%");
//      System.out.println(builder.toString());
        
        return builder.toString();
    }
    
    private String createArtistArea(Track track) {
        StringBuilder builder = new StringBuilder();
        builder.append("Artist: ");
        builder.append(track.getArtist());
        builder.append(System.lineSeparator());
        builder.append("Duration: ");
        int minutes = track.getDuration() / 60;
        int seconds = track.getDuration() % 60;
        builder.append(minutes);
        builder.append(" minutes, ");
        builder.append(seconds);
        builder.append(" seconds");
        builder.append(System.lineSeparator());
        builder.append("Quality: ");
        builder.append(track.getQuality());
        
        return builder.toString();
    }
    
    public class MusicDownloadModel {
         
        private final List<Track> downloads;
        
        public MusicDownloadModel() {
            this.downloads = new ArrayList<>();
            
            Track track = new Track("Bandaga", "Otra Copa", "0.6 kbytes", 216);
            track.setPercentDownloaded(42);
            addDownload(track);
            addDownload(new Track("Bandaga", "Ahora Dice Que Me Ama", "0.6 kbytes", 198));
            addDownload(new Track("Camin", "Tu Nombre (feat. JC Reyes, El Daddy) - Remix", 
                    "0.6 kbytes", 246));
            addDownload(new Track("Bandaga", "Como Tu", "0.6 kbytes", 205));
            addDownload(new Track("Pablo Alboran", "Liueve Sobre Mo Jado", "0.6 kbytes", 228));
        }
        
        public void addDownload(Track track) {
            this.downloads.add(track);
        }

        public List<Track> getDownloads() {
            return downloads;
        }
            
    }
    
    public class Track {
        
        private int percentDownloaded;
        private final int duration;
        
        private final String artist, quality, title;
        
        private final BufferedImage albumCover;

        public Track(String artist, String title, String quality, int duration) {
            this.artist = artist;
            this.title = title;
            this.quality = quality;
            this.duration = duration;
            this.percentDownloaded = 0;
            
            this.albumCover = new BufferedImage(40, 20, BufferedImage.TYPE_INT_RGB);
            Graphics g = albumCover.getGraphics();
            g.setColor(Color.BLUE);
            g.fillRect(0, 0, albumCover.getWidth(), albumCover.getHeight());
            g.dispose();
        }

        public int getPercentDownloaded() {
            return percentDownloaded;
        }

        public void setPercentDownloaded(int percentDownloaded) {
            this.percentDownloaded = percentDownloaded;
        }

        public int getDuration() {
            return duration;
        }

        public String getArtist() {
            return artist;
        }

        public String getQuality() {
            return quality;
        }

        public String getTitle() {
            return title;
        }

        public BufferedImage getAlbumCover() {
            return albumCover;
        } 
        
    }

}

Answer 2

BoxLayout 尊重添加到其中的组件的最小和最大尺寸。

默认情况下，JPanel 没有最大大小，因此它会增长以填充可用空间。

因此，一种解决方案是覆盖面板的getMaximumSize()方法，使其等于首选大小。

a) 如下运行代码以查看默认行为。 单击“添加行”按钮以查看添加行时布局如何更改。

b) 然后在更改getMaximumSize()方法以使用首选大小后重复。

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

public class BoxLayoutRow extends JPanel
{
    private int rowIndex;
    private JPanel rowPanel;

    public BoxLayoutRow()
    {
        setLayout( new BorderLayout() );

        rowPanel = new JPanel();
        rowPanel.setLayout( new BoxLayout(rowPanel, BoxLayout.Y_AXIS) );

        add(new JScrollPane(rowPanel), BorderLayout.CENTER);

        JButton addRow = new JButton("Add Row");
        add(addRow, BorderLayout.PAGE_END);

        addRow.addActionListener((e) -> this.addRow());
    }

    private void addRow()
    {
        rowIndex++;

        JPanel row = new JPanel()
        {
            @Override
            public Dimension getMaximumSize()
            {
                return super.getMaximumSize();
                //return getPreferredSize();
            }
        };

        row.setAlignmentX(0.0f);

        row.add( new JLabel("Row: " + rowIndex) );
        row.setBorder(BorderFactory.createLineBorder(Color.RED));

        rowPanel.add( row );
        revalidate();
        repaint();
    }

    private static void createAndShowUI()
    {
        JFrame frame = new JFrame("BoxLayoutRow");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new BoxLayoutRow() );
        frame.setSize(400, 200);
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(() -> createAndShowUI());
    }
}