在JFrame中实现CardLayout并根据特定的按钮按下来切换卡

Question

我已经在下面发布了我的代码。我有创建可导航GUI的简单任务。我花了过去的几个小时研究如何实现此目标，这是我编写的代码。

本来我想在没有任何布局或任何内容的情况下执行导航。用户单击欢迎面板上的“登录”按钮后，我需要显示主页面板。

它可以很好地显示欢迎卡，但是当我进入validateLogin方法（按下登录按钮时将被激活，并且成功登录后，它应显示卡中的主面板），即使我仍然停留在欢迎面板上已经验证我的程序已到达循环以通过system.out.Println（）更换卡

请帮忙。我花了整个星期六试图通过试验和研究解决这一问题，但没有成功。这对我来说是不得已的办法，因此，如果有人可以向我展示我的缺点，那么我会很乐意继续前进并进行修复。然后将该修复程序应用于我的程序所需的许多其他卡。

    enter code here
    public class mainGUI implements ActionListener{
JFrame main;
JPanel cards = new JPanel(new CardLayout());
CardLayout cl = (CardLayout)(cards.getLayout());

//Items for the welcome panel
JPanel welcome = welcomePanel();
JButton login;
JButton register;
JTextField username;
JTextField password;

//home panel
JPanel home = homePanel();


//WelcomePanel welcome = new WelcomePanel();

ArrayList<Student> students = new ArrayList<Student>();
Student workingStudent;


/**
 * calls load() at start and save() on exit
 * 
 */
public mainGUI(){
    load();

    main = new JFrame();
    main.setSize(900, 600);
    main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    main.setTitle("MyCourses 2k16");
    main.setContentPane(welcomePanel());

    //fill out the cards
    cards.add(welcome, "Welcome");
    cards.add(home, "Home");
            //display welcome card
    cl.show(cards, "welcome");

    main.setVisible(true);

    saveState();
}

private JPanel welcomePanel() {
    JPanel welcome = new JPanel();
    welcome.setLayout(null);
    welcome.setBackground(Color.DARK_GRAY);

    JLabel hi = new JLabel("Welcome to MyCourses 2K16");
    hi.setSize(800, 100);
    hi.setLocation(50,50);
    hi.setFont(new Font("Serif", Font.BOLD, 48));
    hi.setForeground(Color.WHITE);

    JLabel select = new JLabel("Fill in the information, then click login or register to proceed, no special characters allowed");
    select.setSize(700,100);
    select.setLocation(75,100);
    select.setFont(new Font("Serif", Font.PLAIN, 18));
    select.setForeground(Color.WHITE);

    login = new JButton( "login");
    login.setSize(100, 50);
    login.setLocation(50, 200);
    login.addActionListener(this);

    register = new JButton( "register");
    register.setSize(100,50);
    register.setLocation(200, 200);
    register.addActionListener(this);

    JLabel un = new JLabel("username");
    un.setSize(100, 30);
    un.setLocation(50, 270);
    un.setForeground(Color.WHITE);

    username = new JTextField();
    username.setSize(200, 30);
    username.setLocation(50,300);

    JLabel pw = new JLabel("password");
    pw.setSize(100, 30);
    pw.setLocation(50, 350);
    pw.setForeground(Color.WHITE);

    password = new JTextField();
    password.setSize(200, 30);
    password.setLocation(50,380);

    welcome.add(hi);
    welcome.add(select);
    welcome.add(login);
    welcome.add(register);
    welcome.add(un);
    welcome.add(username);
    welcome.add(pw);
    welcome.add(password);

    return welcome;
}

private JPanel homePanel() {
    JPanel home = new JPanel();
    home.setLayout(null);
    home.setBackground(Color.DARK_GRAY);

    JLabel hi = new JLabel("HOME");
    hi.setSize(800, 100);
    hi.setLocation(50,50);
    hi.setFont(new Font("Serif", Font.BOLD, 48));
    hi.setForeground(Color.WHITE);

    return home;

}

public void load(){

}

private void saveState(){
    Iterator<Student> it = students.iterator();
    while(it.hasNext()){
        it.next().saveStudent();
    }
}



public static void main(String[] args) {

    new mainGUI();

}


@Override
public void actionPerformed(ActionEvent e) {
    if (e.getSource()==login){
        System.out.println("Logging in...");
        validateLogin(students);
    }
    else if (e.getSource()==register){

    }
}

private void validateLogin(ArrayList<Student> students){
    boolean valid = false;

    for(int i = 0; i < students.size(); i++){

        if(username.getText().equals(students.get(i).getUsername())
                && password.getText().equals(students.get(i).getPassword()))
        {   
            valid = true;
            workingStudent=(students.get(i));
            System.out.println("Successful Login!");
            cl.show(cards, "home");
        }
    }
    if(valid == false){
        System.out.println("Invalid Login, try again");
    }

}

}

Answer 1

您创建了一个使用CardLayout和卡片的JPanel，但是没有添加任何内容，因此它当然不会显示自身，也不会显示卡片。解决方案：将此JPanel添加到您的GUI。

所以代替：

main.setContentPane(welcomePanel());

做：

main.setContentPane(cards);

问题编号2：

将字符串用作键的类型时，请使用字符串常量。请注意，您因此将一个JPanel添加到卡JPanel中：

cards.add(home, "Home");

但是，然后尝试像这样显示它：

cl.show(cards, "home");

但是“家”与“家”不同。

而是声明一个常量HOME：

public static final String HOME = "home";

并使用相同的常量添加并显示JPanel。

举一个简单的例子：

import java.awt.CardLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class MainGui2 extends JPanel {
    private CardLayout cardLayout = new CardLayout();
    private WelcomePanel welcomePanel = new WelcomePanel(this);
    private HomePanel homePanel = new HomePanel();

    public MainGui2() {
        setLayout(cardLayout);
        add(welcomePanel, WelcomePanel.NAME);
        add(homePanel, HomePanel.NAME);
    }

    public void showCard(String name) {
        cardLayout.show(this, name);
    }

    private static void createAndShowGui() {
        MainGui2 mainPanel = new MainGui2();

        JFrame frame = new JFrame("MainGui2");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }

}

class WelcomePanel extends JPanel {
    public static final String NAME = "welcome panel";
    private MainGui2 mainGui2;

    public WelcomePanel(final MainGui2 mainGui2) {
        this.mainGui2 = mainGui2;
        add(new JLabel(NAME));
        add(new JButton(new AbstractAction("Logon") {

            @Override
            public void actionPerformed(ActionEvent e) {
                mainGui2.showCard(HomePanel.NAME);
            }
        }));
    }
}

class HomePanel extends JPanel {
    public static final String NAME = "home panel";

    public HomePanel() {
        add(new JLabel(NAME));
    }
}