Window frame covering graphics content

问题

this is my first post here and I have a question that seems really nooby, but this has been troubling me for the past hour or so.

I'm making a simple JFrame with a JPanel in it, but the Windows 7 border frame appears to be blocking my view of parts of the panel. For instance, if I draw a little square at coordinate 0,0, it will not appear and I suspect it's behind the window frame.

I've tried messing around with pack, setsize, setpreferred size, setresizable, and different layouts, but I can't get it to show the top 20 pixels or so!

This is what I have:

public RedSunGame() {
super("Red Sun");

rs = new JPanel(new BorderLayout(), true);
rs.setPreferredSize(new Dimension(WIDTH, HEIGHT));
add(rs, "Center");

setPreferredSize(new Dimension(WIDTH, HEIGHT));
pack();
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}

EDIT:

Thanks for all of your replies, sorry for the lack of info :)

I'm using a double buffer strategy I saw in a book. gameRender and paintScreen are in a standard game loop. My RedSunGame class extends JFrame. All the relevant code you could ask for in addition to above:

private static final int WIDTH = 500;
private static final int HEIGHT = 500;
private JPanel rs;
private Graphics2D g2d;
private Image dbImage;

private void gameRender() {
//create buffer
if (dbImage == null){
  dbImage = createImage(WIDTH, HEIGHT);
  g2d = (Graphics2D)dbImage.getGraphics();
}
//clear screen
g2d.setColor(Color.white);
g2d.fillRect(0, 0, WIDTH, HEIGHT);

g2d.setColor(Color.blue);
g2d.setFont(font);
g2d.drawString("FPS: " + FPS, 0, HEIGHT);
g2d.fillRect(30, 30, 10, 10);
}

private void paintScreen() {
Graphics g;
try {
  g = getGraphics();
  if ((g != null) && (dbImage != null))
    g.drawImage(dbImage, 0, 0, null);
  Toolkit.getDefaultToolkit().sync();
  g.dispose();
}
catch (Exception e)
{ System.out.println("Graphics context error: " + e);  }
}

With my current settings it looks like this. http://i.imgur.com/qaabC.png

This is what happens if I have g2d.fillRect(30, 30, 10, 10), the only change being the coordinates 30,30 instead of 0,0. It's definitely hiding behind the border up top. http://i.imgur.com/uzfFe.png

Also, setting it to BorderLayout.CENTER doesn't seem to make a difference in any of these cases.

(sorry it won't let new users post images)

EDIT: I figured it out. I was drawing directly to the JFrame. @Guillaume Polet I see why you shouldn't override the paint method of JFrames as it draws to the frame and not the panel that should actually display content!! Thanks

回答1:

Here is a sample code that shows how your goal can be achieved. Try to spot the differences with your code to find what is wrong:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class RedSunGame {

    private static final int SQUARE_SIZE = 20;
    private JPanel rs;
    private JFrame frame;

    private void initUI() {
        frame = new JFrame("Red Sun");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        rs = new JPanel(new BorderLayout()) {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(Color.YELLOW);
                g.fillRect(0, 0, SQUARE_SIZE, SQUARE_SIZE);
            }

            @Override
            public Dimension getPreferredSize() {
                Dimension preferredSize = super.getPreferredSize();
                // Let's make sure that we have at least our little square size.
                preferredSize.width = Math.max(preferredSize.width, SQUARE_SIZE);
                preferredSize.height = Math.max(preferredSize.height, SQUARE_SIZE);
                return preferredSize;
            }
        };
        frame.add(rs);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                RedSunGame redSunGame = new RedSunGame();
                redSunGame.initUI();
            }
        });
    }
}

回答2:

Verify that WIDTH and HEIGHT are > 0.

Try this:

//add(rs, "center");
add(rs, BorderLayout.CENTER);

回答3:

you may got your answer but for a newbie to java swing i suggest that you should the Net-beans IDE. it graphically adds and lays out the GUI and you dont need to write any hand-written code. It's a great place to start, as stated here:

http://docs.oracle.com/javase/tutorial/uiswing/learn/index.html

来源：https://stackoverflow.com/questions/11131654/window-frame-covering-graphics-content

标签

java

swing

user-interface

jpanel