repaint（）方法不会绘制新框架

Question

I have looked at a lot of answers but i still cannot find a solution. I have a JFrame and two JPanels. I want to remove the one panel and replace it with the second when a button is pressed, but the repaint() method does not refresh the frame. Please help.

Here is my code for the frame:

import javax.swing.*;
import java.awt.*;
import static javax.swing.JFrame.EXIT_ON_CLOSE;

public class MainFrame
{
    static JFrame mainFrame;

    int height = 650;
    int width = 1042;

    public MainFrame()
    {
        mainFrame = new JFrame();
        mainFrame.setBounds(0, 0, width, height);
        mainFrame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        mainFrame.setResizable(false);
    }

    public static void main(String[] args)
    {
        new MainMenu();
        mainFrame.setVisible(true);
    }
}

This is the code for my MainMenu panel

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import static java.awt.Color.CYAN;
import static java.awt.Color.red;

public class MainMenu extends MainFrame
{
    public MainMenu()
    {
        components();
    }

    //variable decleration
    JPanel menuPanel;
    JLabel title;
    JButton periodicTable;

    private void components()
    {
        int buttonW = 500;
        int buttonH = 50;

        //creating panel
        menuPanel = new JPanel();
        menuPanel.setLayout(null);
        menuPanel.setBackground(CYAN);

        //creating title label
        title = new JLabel("Application Title", SwingConstants.CENTER);
        title.setFont(new Font("Calibri Body", 0, 50));
        title.setBounds(width / 3 - buttonW / 2, 50, buttonW, buttonH + 10);

        //creating periodic table button
        periodicTable = new JButton();
        periodicTable.setText("Periodic Table");
        periodicTable.setBounds(width / 3 - buttonW / 2, 50 + buttonH + 60, buttonW, buttonH);
        periodicTable.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
        {
            periodicTableActionPerformed(event);
        }
        });

        //adding components to panel
        menuPanel.add(title);
        menuPanel.add(periodicTable);

        //adding panel to MainFrame
        mainFrame.add(menuPanel);
    }

    private void periodicTableActionPerformed(ActionEvent event)
    {
        mainFrame.remove(menuPanel);
        mainFrame.repaint();
        new PeriodicTable();
        mainFrame.repaint();
    }
}

And finally my PeriodicTable panel

import javax.swing.*;
import java.awt.*;

public class PeriodicTable extends MainFrame
{
    public PeriodicTable()
    {
        periodicComponents();
    }

    JPanel ptPanel;

    private void periodicComponents()
    {
        ptPanel = new JPanel();
        ptPanel.setLayout(null);
        ptPanel.setBackground(Color.RED);
        mainFrame.add(ptPanel);
    }
}

Answer 1

I have no idea why you are extending MainFrame. Looks unnecessary to me.

I want to remove the one panel and replace it with the second when a button is pressed

Then use a CardLayout . Read the section from the Swing tutorial on How to Use CardLayout for a working example.

The tutorial will show you how to better structure your code.

Answer 2

Your PeriodicTable extends MainFrame . When creating new PeriodicTable you create with it new MainFrame which has its own instance of JFrame (MainFrame.mainFrame). You need to add that panel to existing mainFrame in MainMenu

I suggest removing changing your PeriodicTable class like this:

import javax.swing.*;
import java.awt.*;

public class PeriodicTable extends JPanel // Not MainFrame, but new custom panel
{
    public PeriodicTable()
    {
        periodicComponents();
    }


    private void periodicComponents()
    {
        // You don't need ptPanel anymore, because `this` is JPanel
        setLayout(null);
        setBackground(Color.RED);
    }
}

and change your actionPerformed function to something like this:

    private void periodicTableActionPerformed(ActionEvent event)
    {
        mainFrame.remove(menuPanel); // Remove old panel

        mainFrame.add(new PeriodicTable()); // Create and add to existing mainFrame
        mainFrame.repaint(); // Just one repaint at the end
        // I think it will work even without repaint, because add and remove should schedule repainting as well
    }