CardLayout 没有显示 JPanel

Question

我正在为数据库制作表单，我想使用 CardLayout。 我解释一下情况：用户有两个选择：要么连接到他的帐户，要么他是新用户并且需要创建一个帐户。 我有一个带有表单的第一个面板和另一个用于测试的面板（我将背景设置为黑色，以便在用户单击“新建”按钮时查看更改）。当我启动主程序时，我只有带有标题的窗口，没有别的。或者这不是我想要的，我的应用程序的第一步是显示表单。因此，如果有人能解释我的错误在哪里，我会接受它:)

public class Accueil extends JFrame implements ActionListener {

    private CardLayout l = new CardLayout();
    private JPanel main = new JPanel(l);
    private JPanel change = new JPanel();
    private JPanel home = new JPanel(new BorderLayout());
    private JPanel title = new JPanel();
    private JPanel login = new JPanel(new BorderLayout());
    private JPanel login_title = new JPanel();
    private JPanel login_info = new JPanel();
    private JPanel copyright = new JPanel();
    private JLabel welcome = new JLabel("TEST");
    private JLabel connexion = new JLabel("Connexion");
    private JLabel mail = new JLabel("Mail : "); 
    private JTextField input_mail = new JTextField();
    private JLabel mdp = new JLabel("Password : ");
    private JTextField input_mdp = new JTextField();
    private JLabel who = new JLabel ("Are you a  : ");
    private JRadioButton client = new JRadioButton("Client", true);
    private JRadioButton developpeur = new JRadioButton("Developer", false);
    private ButtonGroup bg = new ButtonGroup();
    private JButton ok = new JButton("Login");
    private JButton annule = new JButton("Cancel");
    private JButton inscription = new JButton("New ?");
    private JLabel align = new JLabel("");

    public Accueil() {

        init_title();
        init_login();
        add_button();
        organize_frame();
        inscription.addActionListener(this);
        main.add(home, "Home");
        main.add(change, "Change");
        l.show(main, "Home");
        change.setBackground(Color.black);
        this.setTitle("test");
        this.setSize(600,600);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    public void actionPerformed(ActionEvent arg0) {
        l.show(main, "Change");
    }

    private void organize_frame() { 
        home.add(title, BorderLayout.NORTH);
        home.add(login, BorderLayout.CENTER);
        home.add(copyright, BorderLayout.SOUTH);
    }

    private void init_title() { 
        welcome.setFont(build_font(35));
        welcome.setBorder(new EmptyBorder(20,0,0,0));
        title.setPreferredSize(new Dimension(600,80));
        title.add(welcome);
    }

    private void init_login() {
        setConnexion();
        user_input();
        align.setPreferredSize(new Dimension(215,50));
        organize_button();
        login.add(login_title, BorderLayout.NORTH);
        login.add(login_info, BorderLayout.CENTER);
    }

    private void setConnexion() {
        connexion.setFont(build_font(30));
        connexion.setBorder(new EmptyBorder(20,0,0,0));
        login_title.add(connexion);
        login_title.setPreferredSize(new Dimension(600,100));
    }

    private void user_input() {
        who.setFont(build_font(25));
        mail.setFont(build_font(25));
        mail.setBorder(new EmptyBorder(0,120,0,0));
        mdp.setFont(build_font(25));
        input_mdp.setFont(build_font(25));
        input_mail.setFont(build_font(25));
        input_mail.setPreferredSize(new Dimension(300,40));
        input_mdp.setPreferredSize(new Dimension(300,40));
        who.setFont(build_font(20));
        client.setFont(build_font(20));
        developpeur.setFont(build_font(21));
        login_info.add(who);
        login_info.add(client);
        login_info.add(developpeur);
        login_info.add(mail);
        login_info.add(input_mail);
        login_info.add(mdp);
        login_info.add(input_mdp);
        login_info.add(align);
    }

Answer 1

你在哪里添加使用 JPanel 的 CardLayout，main，什么？

回答：你没有。要让它工作，必须将它添加到最终通向顶层窗口的组件中。必须显示它才能显示其“卡片”。