按下按钮后java在jframe中不显示jpanel

Question

I am simply making a user interface and all i want it to do after the button is pressed is display thanks... I am pretty new to this but from what i see there are no errors? I have tried playing around with the set visible and to no avail...Any help is great thanks

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.Border;
import javax.swing.JTextField;
import javax.swing.JLabel;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JList;





public class GuiApp1 {
  public static void main(String args[]) {
    String title = (args.length == 0 ? "CheckBox Sample" : args[0]);
    JFrame frame = new JFrame(title);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    final JPanel panel = new JPanel(new GridLayout(0, 1));
    Border border = BorderFactory.createTitledBorder("Pizza Toppings");
    panel.setBorder(border);
    JLabel label1 = new JLabel("Enter name below:");
    panel.add(label1);
    JTextField field = new JTextField(20);
    panel.add(field);
    JCheckBox check = new JCheckBox("Car0");
    panel.add(check);
    check = new JCheckBox("Car1");
    panel.add(check);
    check = new JCheckBox("Car2");
    panel.add(check);
    check = new JCheckBox("Car3");
    panel.add(check);
    check = new JCheckBox("Car4");
    panel.add(check);
    JButton button = new JButton("Submit");


    final JPanel listPanel = new JPanel();
    listPanel.setVisible(false);
    JLabel listLbl = new JLabel("Vegetables:");

    listPanel.add(listLbl);



    button.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent event)
        {
            listPanel.setVisible(!listPanel.isVisible());
            panel.setVisible(!panel.isVisible());


        }
    });
    Container contentPane = frame.getContentPane();
    contentPane.add(panel, BorderLayout.CENTER);
    contentPane.add(button, BorderLayout.SOUTH);
    frame.setSize(300, 300);
    frame.setResizable(true);
    frame.setVisible(true);
    frame.setLocationRelativeTo(null);
  }
}

Answer 1

The reason for the vegetables panel not appearing is simple: Xou never add ist to the contentPane .

For the code to function properly you need to add/remove the panels in the ActionListener of the button:

button.addActionListener(new ActionListener()
{
    @Override
    public void actionPerformed(ActionEvent event)
    {
        listPanel.setVisible(!listPanel.isVisible());
        panel.setVisible(!panel.isVisible());

        if (listPanel.isVisible()) {
            contentPane.remove(panel); // Vegetables are visible, so remove the Cars
            contentPane.add(listPanel, BorderLayout.CENTER); // And add the Vegetables
        } else {
            contentPane.remove(listPanel); // Vice versa
            contentPane.add(panel, BorderLayout.CENTER);
        }
    }
});

Then, you need to move the ActionListener below the contentPane declaration and make it final .

Also you should consider putting the different checkboxes is different variables, so you can read the state of them. If you don't want to have so many variables hanging you could put them into an array.

JCheckBox[] checks = new JCheckbox[5];
checks[0] = new JCheckBox("Car0");
panel.add(checks[0]);
...