嵌套的BoxLayout不工作

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，它创建了一个带有一些添加组件的面板CPanel.java。我的应用程序布局如下:
Main类用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(一个带有添加组件的面板)并将其添加到主面板。CPanel对象也有其组件的BoxLayout。问题是，CPanel面板没有合并BoxLayout，而是坚持流布局。这是我的类的代码…

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

似乎您希望CPanel具有JScrollPane，其与BoxLayout一起作为组件出现。您创建JPanel，设置其布局并将其添加到JScrollPane是正确的，但您仍然需要将JScrollPane添加到CPanel，将按钮和demo添加到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);
    }
}