嵌套的 BoxLayout 不起作用？

Question

我创建了两个 java 类，其中一个是我的主类 main.java，另一个是支持类，它创建一个面板，其中包含一些添加的组件 CPanel.java。我的应用程序的布局如下：
Main 类使用 BoxLayout 创建一个主面板，并在顶部添加一个工具栏，然后创建一个 CPanel 对象（带有添加组件的面板）并将其添加到主面板。 CPanel 对象还具有用于其组件的 BoxLayout。问题是，CPanel 面板没有合并 BoxLayout，它只是坚持流式布局。这是我的课程的代码..

public class MainFile extends JFrame {
        private JToolBar navbar ;
        private JButton backBtn, forwardBtn, homeBtn ;
        private CPanel content ;
        private static JPanel app = new JPanel() ;
        public MainFile(){
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        navbar = new JToolBar() ;
        navbar.setMaximumSize(new Dimension(1000, 50));
        setSize(500, 800) ;
        app.setLayout(new BoxLayout(app, BoxLayout.PAGE_AXIS));
        app.add(navbar , BorderLayout.NORTH ) ;

        ImageIcon leftButtonIcon = createImageIcon("images/right.gif");
        ImageIcon middleButtonIcon = createImageIcon("images/middle.gif");
        ImageIcon rightButtonIcon = createImageIcon("images/left.gif");

        backBtn = new JButton(leftButtonIcon) ;
        forwardBtn = new JButton(rightButtonIcon) ;
        homeBtn = new JButton(middleButtonIcon) ;
        navbar.add(forwardBtn) ;
        navbar.add(Box.createGlue());
        navbar.add(homeBtn) ;
        navbar.add(Box.createGlue());
        navbar.add(backBtn) ;

        content = new CPanel() ;
        app.add(content) ;
        setContentPane(app) ;

    }
    protected static ImageIcon createImageIcon(String path) {
        java.net.URL imgURL = MFrame.class.getResource(path);
        if (imgURL != null) {
            return new ImageIcon(imgURL);
        } else {
            System.err.println("Couldn't find file: " + path);
            return null;
        }
    }
    public static void showGUI(){
        MFrame Reader = new MFrame() ;
        //Reader.pack();
        //Reader.setContentPane(app);
        Reader.setVisible(true) ;
    }
    public static void main(String args[]){
        SwingUtilities.invokeLater(new Runnable(){
            @Override
            public void run(){
                showGUI() ;
            }
        });
    }
}

这是我的 CPanel 类

public class CPanel extends JPanel {
    private JScrollPane scrollPane ;
    private JPanel content ;
    private JEditorPane demo ;
    public CPanel(){
        scrollPane = new JScrollPane() ;
        content = new JPanel() ;
        scrollPane.setViewportView(content);
        content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS));
        try{
         java.net.URL text = CPanel.class.getResource("demo.txt") ;
        demo = new JEditorPane(text) ;
        }catch(Exception e){
            System.out.println("Something bad happened with the file") ;
        }
        add(demo) ;
        JButton demob = new JButton("Button 1") ;
        JButton demob2 = new JButton("Button 2") ;
        add(demob) ;
        add(demob2) ;
    }
}

Answer 1

您似乎希望CPanel 有一个JScrollPane，它显示为带有BoxLayout 的组件。您在创建JPanel、设置其布局并将其添加到JScrollPane 时是正确的，但您仍然需要将JScrollPane 添加到您的CPanel 和按钮以及demo 到content

public class CPanel extends JPanel {
    private JScrollPane scrollPane ;
    private JPanel content ;
    private JEditorPane demo ;

    public CPanel(){

        scrollPane = new JScrollPane() ;
        content = new JPanel() ;
        scrollPane.setViewportView(content); 
        content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS));

        try{
         java.net.URL text = CPanel.class.getResource("demo.txt") ;
        demo = new JEditorPane(text) ;
        }catch(Exception e){
            System.out.println("Something bad happened with the file") ;
        }

        //These need to be added to the contentpanel
        content.add(demo) ;
        JButton demob = new JButton("Button 1") ;
        JButton demob2 = new JButton("Button 2") ;
        content.add(demob) ;
        content.add(demob2) ;

        //Here we need to add the scrollPane, to which the JPanel 
        //with BoxLayout has been added
        this.setLayout(new BorderLayout());
        this.add(scrollPane, BorderLayout.CENTER);
    }
}