Java CardLayout不显示

Question

我有一个游戏，已经运行和工作，我想添加一个标题屏幕到它。我正在尝试添加一个CardLayout，以便在游戏和标题屏幕之间轻松切换。我目前的问题是什么都没有显示出来。这是一张图片：http://i.imgur.com/kVIXYQ7.png。当我运行它时，我只是得到一个空白的JPanel。我做错了什么？

public class UI
{
private static JPanel cards;
private static CardLayout cardLayout;

public static void main(String args[])
    {new UI();}

public UI()
{
    JFrame frame = new JFrame("Scrolling Shooter");

    frame.setResizable(false);
    Toolkit tk = Toolkit.getDefaultToolkit();  
    int width = ((int) tk.getScreenSize().getWidth());  
    int height = ((int) tk.getScreenSize().getHeight());  
    frame.setSize(width, height);

    TitleScreen title = new TitleScreen(frame);
    ScrollingShooter game = new ScrollingShooter(frame);

    cards = new JPanel(new CardLayout());
    cards.add(title, "title");
    cards.add(game, "game");
    cards.setOpaque(true);
    frame.getContentPane().add(cards);

    cardLayout = (CardLayout) cards.getLayout();
    cardLayout.first(cards);

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

/**
 * Switches to the next screen
 */
public static void nextScreen()
    {cardLayout.next(cards);}

/**
 * Returns to the first screen
 */
public static void firstScreen()
    {cardLayout.first(cards);}
}

Answer 1

您还没有将Cards添加到任何内容。

尝试将Cards添加到框架，然后使框架可见

例如..。

JFrame frame = new JFrame("Scrolling Shooter");

TitleScreen title = new TitleScreen(frame);
ScrollingShooter game = new ScrollingShooter(frame);

cards = new JPanel(new CardLayout());
cards.add(title, "title");
cards.add(game, "game");
cards.setOpaque(true);

cardLayout = (CardLayout) cards.getLayout();
cardLayout.first(cards);

frame.add(cards);
//...
frame.setResizable(false);
frame.setSize(width, height);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);

仅供参考:您应该在设置框架大小之前使用setResizable，因为setResizable可以更改框架的边框插入