调整框架（窗口）大小后组件消失

Question

当我在主页或 page2 上时，一切看起来都不错，但是当我点击 page3 并调整框架（窗口）的大小时，page3 的内容将消失，并会在鼠标悬停时出现。

之后，如果我点击 page2 或主页，它们的内容也不会出现。

我正在用 java 制作一个测验应用程序。

package quizPro;
import javax.swing.*;
public class mainclass {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                     new mainclass();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public mainclass() {
        new MLayout();
    }
}

---

package quizPro;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import com.sun.prism.Graphics;
import net.miginfocom.swing.MigLayout;

public class MLayout  {
    JFrame frame = new JFrame("Employees");
    JPanel panel = new JPanel();
    JPanel panel2 = new JPanel();
    JPanel panel3 = new JPanel();
    JButton btnHome = new JButton("Home");
    JButton btnPage2 = new JButton("Page 2");
    JLabel lblDsc = new JLabel("Description : ");
    JTextArea txaDsc = new JTextArea(10,70);
    //JTextArea txaDsc2 = new JTextArea(10,50);
    Page2 page3 = new Page2();

    public MLayout() {
        frame.setVisible(true);
        panel.setLayout(new MigLayout());
        panel2.setLayout(new MigLayout());
        panel3.setLayout(new MigLayout());
        panel.add(btnHome, "skip, split2");
        btnHome.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                frame.add(panel2);
                frame.remove(panel3);
                page3.remove();
                btnPage2.setEnabled(true);
                panel2.revalidate();    
                panel2.repaint();
            }
        }); 
        panel.add(btnPage2, "wrap");
        btnPage2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                frame.remove(panel2);               
                page3.thirdpage(frame, panel3);
                frame.add(panel3);
                page3.remove();
                panel3.revalidate();
                panel3.repaint();
            }
        });

        panel2.add(lblDsc, "top");
        panel2.add(new JScrollPane(txaDsc), "push, grow");
        //panel3.add(new JScrollPane(page3.thirdpage(panel3)), "push,         grow");
        frame.add(panel, BorderLayout.NORTH);
        frame.add(panel2);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
}

---

package quizPro;
import java.awt.Component;
import java.awt.event.*;
import javax.swing.*;
import net.miginfocom.swing.MigLayout;

public class Page2  {
       JButton btnPage3 = new JButton("Page 3");
       JPanel panel4 = new JPanel();
       Page3 medium = new Page3();
       public Component thirdpage(JFrame frame, JPanel panel3) {
        panel4.setLayout(new MigLayout()); 
        panel3.add(btnPage3, "wrap");
        btnPage3.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                panel3.removeAll();             
                medium.mediumquiz(panel4);
                frame.add(panel4);
                panel4.revalidate();
                panel4.repaint();
            }
        }); 
        return null;
    }    
    public void remove() {
        panel4.removeAll();

    }
}

---

package quizPro;
import java.awt.Component;
import javax.swing.*;

public class Page3 {    
       JButton newbtn12 = new JButton("Now resize the frame or window");
       public Component mediumquiz(JPanel panel4) {
           panel4.add(newbtn12, "wrap");
          return null;
       }
}

Answer 1

所以，问题出在 btnPage3。因为您正在创建一个新面板（panel4）并将其添加到 panel3 后面。

你可以这样解决：

btnPage3.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            medium.mediumquiz(panel4);

            frame.add(panel4);                
            frame.remove(panel3);                               
            frame.revalidate();
        }
    });

或者你可以再次使用 panel3，像这样：

    panel3.removeAll();
    panel3.add(btnPage3, "wrap");

    btnPage3.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            panel3.removeAll();

            medium.mediumquiz(panel3);

            panel3.revalidate();
            panel3.repaint();
        }
    });