Drawing in multiple JPanels contained in one JPanel

问题

I have a class which extends JPanel which contain 3 other panels. I want to draw into the 3 panels. Here's what my code must be like, what am i doing wrong ? I just have an empty frame after execution.

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Thumbnail extends JPanel {

    private JPanel bigPanel;
    private JPanel panelOne;
    private JPanel panelTwo;
    private JPanel panelThree;

    public Thumbnail() {

        panelOne = new JPanel() {
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.black);
                g.drawString("writing something", 10, 10);
                g.drawRect(10, 10, 50, 50);
            }
        };
        bigPanel = new JPanel();
        bigPanel.add(panelOne);
        this.setLayout(new FlowLayout(FlowLayout.LEFT));
        this.add(bigPanel);
        //other codes...
    }

    public static void main(String[] args) {
        JFrame jf = new JFrame();
        Thumbnail tb = new Thumbnail();
        jf.add(tb);
        jf.pack();
        jf.setVisible(true);
    }
}

回答1:

panelOne is not providing any layout information to the layout manager, which means, by default, it's preferred size is 0x0

Try adding something like...

@Override
public Dimension getPreferredSize() {
    return new Dimension(100, 100);
}

to panelOne...

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Thumbnail extends JPanel {

    private JPanel bigPanel;
    private JPanel panelOne;
    private JPanel panelTwo;
    private JPanel panelThree;

    public Thumbnail() {

        panelOne = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.black);
                g.drawString("writing something", 10, 10);
                g.drawRect(10, 10, 50, 50);
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(100, 100);
            }

        };
        bigPanel = new JPanel();
        bigPanel.add(panelOne);
        this.setLayout(new FlowLayout(FlowLayout.LEFT));
        this.add(bigPanel);
        //other codes...
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                JFrame jf = new JFrame();
                jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                Thumbnail tb = new Thumbnail();
                jf.add(tb);
                jf.pack();
                jf.setLocationRelativeTo(null);
                jf.setVisible(true);
            }
        });
    }
}

You might like to take a look at Initial Threads and Laying Out Components Within a Container for more details

回答2:

bigPanel = new JPanel(new GridLayout(3,1));
bigPanel.add(panelOne, BorderLayout.NORTH);
bigPanel.add(panelTwo, BorderLayout.CENTER);
bigPanel.add(panelThree, BorderLayout.SOUTH);

. .

this.getContentPane().add(bigPanel);

EDIT:
It's better to extend a JDialog, and then to add JFrame and then all of your panel, only in case that the purpose is to use JDialog as your container, otherwise, your code is fine.

来源：https://stackoverflow.com/questions/28078693/drawing-in-multiple-jpanels-contained-in-one-jpanel

标签

java

swing

jpanel