Java使用构造函数参数在JFrame中创建cardLayout

Question

我想用CardLayout 和一个参数创建一个JPanel。我有以下代码：

public class MainFrame extends JFrame{

private JPanel contentPane;
private CardLayout cardLayout;
private String card;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                MainFrame frame = new MainFrame("");
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public MainFrame(String card) {
    initComponents();
    cardLayout = new CardLayout();

    if(card.equals("ADMIN")){
        contentPane.revalidate();
        cardLayout.show(this.contentPane, "ADMIN");
    }else if(card.equals("USER")){
        contentPane.revalidate();
        cardLayout.show(this.contentPane, "USER");
    }
}

private void initComponents() {
    Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
    this.setLocation(dim.width/2-this.getSize().width/2, dim.height/2-this.getSize().height/2);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(1280, 800);
    this.contentPane = new JPanel();
    this.contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    this.contentPane.setLayout(cardLayout);
    this.contentPane.add(new PanelOne(), "ADMIN");
    this.contentPane.add(new PanelTwo(), "USER");
    setContentPane(this.contentPane);
}

但是如果我运行这段代码，我会得到一个异常：

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException:
    wrong parent for CardLayout

我该怎么做才能解决这个问题？

我已经尝试在main方法中更改参数，但没有任何解决方案。

Answer 1

您的问题出在您正在使用的 CardLayout 对象中。这个 CardLayout 对象，您用于show 组件：

public MainFrame(String card) {
    initComponents();
    cardLayout = new CardLayout();

和你这里的 contentPane 的布局不一样：

this.contentPane.setLayout(cardLayout);

事实上，后面这个cardLayout变量在使用的时候实际上是null。

解决办法，改成这样：

公共类 MainFrame 扩展 JFrame{

private JPanel contentPane;
private CardLayout cardLayout = new CardLayout();

并且不要在其他地方打电话给new CardLayout();。

---

另一个问题是你在调用构造函数时传入了一个空字符串。

例如，

import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Toolkit;

import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class MainFrame extends JFrame {

    private JPanel contentPane;
    private CardLayout cardLayout = new CardLayout();
    private String card;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainFrame frame = new MainFrame(PanelOne.NAME);
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public MainFrame(String card) {
        initComponents();
        // cardLayout = new CardLayout();        
        cardLayout.show(getContentPane(), card);
    }

    private void initComponents() {
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        this.setLocation(dim.width / 2 - this.getSize().width / 2,
                dim.height / 2 - this.getSize().height / 2);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(1280, 800);
        this.contentPane = new JPanel();
        this.contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        this.contentPane.setLayout(cardLayout);
        this.contentPane.add(new PanelOne(), PanelOne.NAME);
        this.contentPane.add(new PanelTwo(), PanelTwo.NAME);
        setContentPane(this.contentPane);
    }
}

public class PanelOne extends JPanel {
    public static final String NAME = "Administrator";

    public PanelOne() {
        setBorder(BorderFactory.createTitledBorder(NAME));
    }
}

public class PanelTwo extends JPanel {
    public static final String NAME = "User";

    public PanelTwo() {
        setBorder(BorderFactory.createTitledBorder(NAME));
    }

}