为什么我的卡片布局中没有显示第一个面板

Question

抱歉代码转储，但我不确定是哪里导致了问题。 当我单击 Round Robin 按钮时，它应该带我到 RoundRobin 页面（它确实如此），但随后我应该能够单击开始和蓝色的中心面板应该是黄色的黄色动画面板。 当我运行这个时，我只看到黄色的动画面板，当我点击开始时，我得到一个“线程“AWT-EventQueue-0”中的异常java.lang.IllegalArgumentException：CardLayout的错误父级”错误。

/**
     * @description:scheduling algoritmn visualisation app
     * @version: 1.0
     * @date created: 22/11/2020
     */
    
    import javax.swing.*;
    import javax.swing.border.EmptyBorder;
    import java.awt.*;
    import java.awt.event.*;
    import java.awt.image.*;
    import java.io.*;
    import javax.imageio.ImageIO;
    import java.net.*; 
    
    public class SchedulingAlgorithms extends JFrame{
        CardLayout cl;
        JPanel contentPane;
        Container deckPanel;
        Image image;
    
        /**
         * Constructor for objects of class SchedulingAlgorithms
         */
        public SchedulingAlgorithms(){
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setBounds(100, 100, 658, 336);
            contentPane = new JPanel();
            contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
            setContentPane(contentPane);
            contentPane.setLayout(null);
                
            JPanel headerPanel = new JPanel();
            JLabel label = new JLabel();
            headerPanel.setBackground(Color.LIGHT_GRAY);
            headerPanel.setBounds(5, 5, 125, 106);
            contentPane.add(headerPanel);
            
            
            try{
                URL url = new URL("file:C:///Users//alyssa//Scheduling_Animations//icon.png");        
                image=ImageIO.read(url);
                headerPanel.add(new JLabel(new ImageIcon(image)));
            }catch (IOException e) {
                e.printStackTrace();
            } 
            
            
            JPanel btnPanel = new JPanel();
            btnPanel.setBackground(Color.LIGHT_GRAY);
            btnPanel.setBounds(5, 111, 125, 181);
            contentPane.add(btnPanel);
            btnPanel.setLayout(null);
            cl= new CardLayout();
        
            JPanel deckPanel = new JPanel();
            deckPanel.setBounds(140, 5, 492, 287);
            contentPane.add(deckPanel);
            deckPanel.setLayout(cl);
                
            JPanel home = new JPanel();
            deckPanel.add(home, "home");
            
            JPanel homePic = new JPanel(new GridLayout(2,1));
            home.add(homePic, "homePic");
            
            JLabel instructions1 = new JLabel();
            instructions1.setText("Select a scheduling algorithm to see it's visual representation");
            homePic.add(instructions1);
            
            try{
                URL url = new URL("file:C:///Users//alyssa//Scheduling_Animations//schedule.png");        
                image=ImageIO.read(url);
                homePic.add(new JLabel(new ImageIcon(image)));
            }catch (IOException e) {
                e.printStackTrace();
            }                
            JPanel card1 = new JPanel();
            deckPanel.add(card1, "rr");
            card1.setLayout(new BorderLayout());
            
            JLabel txt2= new JLabel();
            txt2.setText("Round Robin: Set the boundaries of the animation");
            card1.add(txt2);
                       
                
            JPanel card2 = new JPanel();
            deckPanel.add(card2, "fcfs");
                
            JTextArea txt3 = new JTextArea();
            txt3.setText("First-Come-First-Served");
            card2.add(txt3);
                
            JPanel card3 = new JPanel();
            deckPanel.add(card3, "sjf");
                
            JTextArea txt4 = new JTextArea();
            txt4.setText("Shortest Job First");
            card3.add(txt4);
                
            JPanel card4 = new JPanel();
            deckPanel.add(card4, "ps");
                
            JTextArea txt5 = new JTextArea();
            txt5.setText("Priority Scheduling");
            card4.add(txt5);
            
            JButton btn0 = new JButton("Home");
            btn0.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    if(e.getActionCommand()=="Home")
                    cl.show(deckPanel, "home");
                }
            });
            btn0.setBounds(10, 11, 89, 23);
            btnPanel.add(btn0);
                
            JButton btn1 = new JButton("Round Robin");
            btn1.setBounds(10, 45, 89, 23);
            btnPanel.add(btn1);
            
            btn1.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {                
                    if(e.getActionCommand()=="Round Robin")
                    cl.show(deckPanel, "rr");
                }
            });
            
                
            JButton btn2 = new JButton("First-Come-First-Served");
            btn2.setBounds(10, 79, 89, 23);
            btnPanel.add(btn2);
            
            btn2.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {                
                    if(e.getActionCommand()=="First-Come-First-Served")
                    cl.show(deckPanel, "fcfs");
                }
            });
                
            JButton btn3 = new JButton("Shortest Job First");
            btn3.setBounds(10, 113, 89, 23);
            btnPanel.add(btn3);
        
            btn3.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {                
                    if(e.getActionCommand()=="Shortest Job First")
                    cl.show(deckPanel, "sjf");
                }
            });
                
            JButton btn4 = new JButton("Priority Scheduling");
            btn4.setBounds(10, 147, 89, 23);
            btnPanel.add(btn4);
            
            btn4.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {                
                    if(e.getActionCommand()=="Priority Scheduling")
                    cl.show(deckPanel, "ps");
                }
            });
            
           JPanel northPanel=new JPanel();
           card1.add(northPanel,BorderLayout.NORTH);
           
           JLabel heading=new JLabel();
           heading.setText("Round Robin.");
           northPanel.add(heading);
           JLabel instructions2= new JLabel();
           instructions2.setText("Set the boundaries of the animation");          
           northPanel.add(instructions2);
           
           JPanel centerPanel=new JPanel();
           centerPanel.setBackground(Color.blue);
           card1.add(centerPanel,BorderLayout.CENTER);
           centerPanel.setLayout(new CardLayout());
           
           JPanel animPanel=new JPanel();
           animPanel.setBackground(Color.yellow);
           centerPanel.add(animPanel,"anim");
           
           
           JPanel southPanel=new JPanel();
           card1.add(southPanel,BorderLayout.SOUTH);
           
           JButton start = new JButton("START");
           start.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                   if(e.getActionCommand()=="START")
                   cl.show(centerPanel, "anim");
               }
           });
           start.setBounds(311, 159, 65, 23);
           southPanel.add(start);           

        }

       public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
            try {
                SchedulingAlgorithms frame = new SchedulingAlgorithms();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
            }
        });
       }
}

Answer 1

您使用变量“cl”作为对布局管理器的引用来设置“deckPanel”的布局：

deckPanel.setLayout(cl);

但是随后您尝试更改“centerPanel”上的卡：

  if(e.getActionCommand()=="START")
     cl.show(centerPanel, "anim");

1. 您不能共享 CardLayout 引用。 如果您希望“centerPanel”也使用 CardLayout，那么您需要为该布局管理器保留一个单独的引用。 因此，对于各个布局管理器，您确实需要“deckLayout”和“centerLayout”变量。 这就是为什么变量名应该是描述性的，这样你就知道如何使用变量。

2. 不要使用“==”进行对象比较。 而是使用equals(...)方法。