JButton的Java Swing绘画问题

Question

What I'm trying to do is to create a desktop application using Swing. I need to add a background image to my frame and also add some buttons on some specific locations which should NOT have their content area filled. So, here is what I've done so far;

public class MainGUI extends JFrame {

  public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                MainGUI window = new MainGUI();
                window.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
  }


  public MainGUI() {
    setUndecorated(true);
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    this.setSize(screenSize);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    initialize();
  }


  private void initialize() {

    JPanel mainPanel = new JPanel() {
        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            try {
                g.drawImage(new ImageIcon(ImageIO.read(new File("a.png"))).getImage(), 0, 0, null);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    };

    mainPanel.setLayout(new BorderLayout());

    JButton btn1 = new JButton();
    btn1 .setAlignmentX(Component.CENTER_ALIGNMENT);
    btn1 .setContentAreaFilled(false);
    btn1 .setBorder(new EmptyBorder(0, 0, 0, 0));
    btn1 .setIcon(new ImageIcon("btn1.png"));

    JPanel rightButtonPanel = new JPanel();
    rightButtonPanel.setLayout(new BoxLayout(rightButtonPanel, BoxLayout.Y_AXIS));
    rightButtonPanel.add(btn1);

    mainPanel.add(rightButtonPanel, BorderLayout.EAST);

    this.setContentPane(mainPanel);

  }

}

When I do this, setContentAreaFilled(false) feature does not work. I suppose it's related to the painting but I'm not sure. Can anyone help me with this please?

Answer 1

So I took your code and modified it.

Primarily:

• Added btn1.setOpaque(false);
• And added rightButtonPanel.setBackground(Color.GREEN);

Example

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class MainGUI extends JFrame {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainGUI window = new MainGUI();
                    window.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public MainGUI() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        initialize();
        pack();
    }

    private void initialize() {

        JPanel mainPanel = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(400, 400);
            }

            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
            }
        };

        mainPanel.setBackground(Color.RED);

        mainPanel.setLayout(new BorderLayout());

        JButton btn1 = new JButton();
        btn1.setAlignmentX(Component.CENTER_ALIGNMENT);
        btn1.setContentAreaFilled(false);
        btn1.setOpaque(false);
        btn1.setBorder(new EmptyBorder(0, 0, 0, 0));
        btn1.setText("This is a test");

        JPanel rightButtonPanel = new JPanel();
        rightButtonPanel.setBackground(Color.GREEN);
        rightButtonPanel.setLayout(new BoxLayout(rightButtonPanel, BoxLayout.Y_AXIS));
        rightButtonPanel.add(btn1);

        mainPanel.add(rightButtonPanel, BorderLayout.EAST);

        this.setContentPane(mainPanel);

    }

}

This produced

So, it's not the buttons (at least at this point) which are at fault.

So, I changed rightButtonPanel.setBackground(Color.GREEN); to rightButtonPanel.setOpaque(false); and it produced