我不明白为什么我得到一个非法参数异常：错误的父卡布局

Question

这是 CardTesting 类，我在其中得到 IllegalArgumentException： CardLayout 的错误父级。该行 cl.show（this， "Panel 2"） 抛出一个 IllegalArgumentException： 错误的 CardLayout 父级。请帮忙！:D

import java.awt.*;
import javax.swing.*;
public class CardTesting extends JFrame {
CardLayout cl = new CardLayout();
JPanel panel1, panel2;
public CardTesting() {
    super("Card Layout Testing");
    setSize(400, 200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLayout(cl);
    panel1 = new JPanel();
    panel2 = new JPanel();
    panel1.add(new JButton("Button 1"));
    panel2.add(new JButton("Button 2"));
    add(panel1, "Panel 1");
    add(panel2, "Panel 2");
    setVisible(true);
}
private void iterate() {
    try {
        Thread.sleep(1000);
    } catch (Exception e) { }
    cl.show(this, "Panel 2");
}
public static void main(String[] args) {
    CardTesting frame = new CardTesting();
    frame.iterate();
}

}

Answer 1

您得到IllegalArguementException，因为您在显示卡片时使用this cl.show(this, "Panel 2");其中this指的是父级JFrame，并且您没有为父级"JFrame"添加任何布局。将卡片封装在JPanel内总是比JFrame更好的方法

您必须将两个卡片/面板添加到父面板，并将布局指定为cardLayout。在这里，我创建了一个作为父级的cardPanel

import java.awt.*;
import javax.swing.*;
public class CardTesting extends JFrame {
    CardLayout cl = new CardLayout();
    JPanel panel1, panel2;
    JPanel cardPanel;
    public CardTesting() {
        super("Card Layout Testing");
        setSize(400, 200);
        this.setLayout(cl);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(cl);
        panel1 = new JPanel();
        panel2 = new JPanel();
        cardPanel=new JPanel();
        cardPanel.setLayout(cl);
        panel1.add(new JButton("Button 1"));
        panel2.add(new JButton("Button 2"));
        cardPanel.add(panel1, "Panel 1");
        cardPanel.add(panel2, "Panel 2");
        add(cardPanel);
        setVisible(true);
    }
    private void iterate() {
        /* the iterate() method is supposed to show the second card after Thread.sleep(1000), but cl.show(this, "Panel 2") throws an IllegalArgumentException: wrong parent for CardLayout*/
        try {
            Thread.sleep(1000);
        } catch (Exception e) {
        }
        cl.show(cardPanel, "Panel 2");
    }
    public static void main(String[] args) {
        CardTesting frame = new CardTesting();
        frame.iterate();
    }
}