具有可折叠 JPanel 的容器的首选布局管理器是什么

Question

我的代码有一个 JPanel，其中包含三个可折叠的 JPanel。外部 JPanel 使用 BoxLayout 垂直堆叠三个 JPanel。但是，当我折叠 JPanel 时，顶部的 JPanel 将始终扩展以填充该区域（即使我 setMaximumSize() 等），而我希望下部的 JPanel 向上扩展。一般都是有故障的。我正在查看 GridBagLayout，它是否更适合这种工作？

谢谢。

这是我最疯狂的梦想中的 VB 图像（标题为“垂直面板”的图像）：

http://www.codeproject.com/KB/cpp/CollapsiblePanelVB.aspx

Answer 1

我不知道什么是可折叠面板。它是否会一直塌陷到 0，或者是否有最小高度？

如果您将最大尺寸管理为始终等于首选尺寸，那么您应该能够使用 BoxLayout。只需确保您还使用：

panel.add( Box.createVerticalGlue() );

在面板底部，以允许胶水使用额外的空间。

我要花很长时间才能从我面前的 500 行垃圾中剪出一个可编译的片段。

这就是创建 SSCCE 并忘记垃圾代码的原因。您所需要的只是一个带有 3 个可折叠面板的面板。然后添加一个按钮来折叠面板，看看会发生什么。最好从演示代码开始，然后编写 500 行代码，然后发现它不起作用。

Answer 2

我强烈建议 MigLayout。它非常强大并且非常容易使用。它也被广泛使用。

Answer 3

或基于 GridBagLayout

import java.awt.*;
import java.awt.event.*;
import java.awt.font.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class ExpansiblePanel {

    public static void main(String[] args) {
        CollapsablePanel cp = new CollapsablePanel("test", buildPanel());
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new JScrollPane(cp));
        f.setPreferredSize(new Dimension(360, 200));
        f.setLocation(150, 150);
        f.pack();
        f.setVisible(true);
    }

    public static JPanel buildPanel() {
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2, 1, 2, 1);
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        JPanel p1 = new JPanel(new GridBagLayout());
        gbc.gridwidth = GridBagConstraints.RELATIVE;
        p1.add(new JButton("button 1"), gbc);
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        p1.add(new JButton("button 2"), gbc);
        gbc.gridwidth = GridBagConstraints.RELATIVE;
        p1.add(new JButton("button 3"), gbc);
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        p1.add(new JButton("button 4"), gbc);
        p1.setBackground(Color.blue);
        return p1;
    }

    private ExpansiblePanel() {
    }
}

class CollapsablePanel extends JPanel {

    private static final long serialVersionUID = 1L;
    private boolean selected;
    private JPanel contentPanel_;
    private HeaderPanel headerPanel_;

    private class HeaderPanel extends JPanel implements MouseListener {

        private static final long serialVersionUID = 1L;
        private String text_;
        private Font font;
        private BufferedImage open, closed;
        final int OFFSET = 30, PAD = 5;

        HeaderPanel(String text) {
            addMouseListener(this);
            text_ = text;
            font = new Font("sans-serif", Font.PLAIN + Font.BOLD, 12);
            // setRequestFocusEnabled(true);
            setPreferredSize(new Dimension(200, 25));
            setBackground(Color.black);
            setForeground(Color.red);
            int w = getWidth();
            int h = getHeight();
            /*try {
            open = ImageIO.read(new File("images/arrow_down_mini.png"));
            closed = ImageIO.read(new File("images/arrow_right_mini.png"));
            } catch (IOException e) {
            e.printStackTrace();
            }*/
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            int h = getHeight();
            /*if (selected)
            g2.drawImage(open, PAD, 0, h, h, this);
            else
            g2.drawImage(closed, PAD, 0, h, h, this);
             */ // Uncomment once you have your own images
            g2.setFont(font);
            FontRenderContext frc = g2.getFontRenderContext();
            LineMetrics lm = font.getLineMetrics(text_, frc);
            float height = lm.getAscent() + lm.getDescent();
            float x = OFFSET;
            float y = (h + height) / 2 - lm.getDescent();
            g2.drawString(text_, x, y);
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            toggleSelection();
        }

        @Override
        public void mouseEntered(MouseEvent e) {
        }

        @Override
        public void mouseExited(MouseEvent e) {
        }

        @Override
        public void mousePressed(MouseEvent e) {
        }

        @Override
        public void mouseReleased(MouseEvent e) {
        }
    }

    CollapsablePanel(String text, JPanel panel) {
        super(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(1, 3, 0, 3);
        gbc.weightx = 1.0;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        selected = false;
        headerPanel_ = new HeaderPanel(text);
        setBackground(Color.orange);
        contentPanel_ = panel;
        add(headerPanel_, gbc);
        add(contentPanel_, gbc);
        contentPanel_.setVisible(false);
        JLabel padding = new JLabel();
        gbc.weighty = 1.0;
        add(padding, gbc);
    }

    public void toggleSelection() {
        selected = !selected;
        if (contentPanel_.isShowing()) {
            contentPanel_.setVisible(false);
        } else {
            contentPanel_.setVisible(true);
        }
        revalidate();
        headerPanel_.repaint();
    }
}