没有调用paintComponent()

Question

My paintComponent() won't get called.

I have Googled a little, and haven't found an answer that I could use. At first, I didn't have the frame.getContentPane().add(this) , and thought that the answer was to insert that, but neither that worked. I hope someone can help me out.

Here you have a little snippet of my code:

package engine;

import java.awt.Graphics;
import java.awt.Graphics2D;

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

public class Frame extends JPanel {
    private static final long serialVersionUID = 1L;
    private JFrame frame = new JFrame();
    private GameEngine engine;
    private Game game;

    public Frame(GameEngine engine) {
        this.engine = engine;
        frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
        frame.setUndecorated(true);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(null);
        frame.setSize(1920, 1080);
        frame.getContentPane().add(this);
    }

    public void updateGame(Game game) {
        this.game = game;
    }

    public JFrame getFrame() {
        return frame;
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        g2d.drawString("" + game.getClockDate(), 1920 - 100, 20);
        System.out.println("test");
    }
}

I'm calling it from here, in another class:

public void loop() {
    if (this.ingame) {
        game.loop();
        frame.updateGame(game);
        frame.repaint();
    }
}

Answer 1

Try calling super() as the first line of your constructor so that your JPanel initializes correctly.

public Frame(GameEngine engine) {
    super();
    this.engine = engine;
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    frame.setUndecorated(true);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(null);
    frame.setSize(1920, 1080);
    frame.getContentPane().add(this);
}

Also call the @Override annotation for getting your code clear.

@Override    
public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        g2d.drawString("" + game.getClockDate(), 1920 - 100, 20);
        System.out.println("test");
}

Answer 2

Please post what context you are trying to paint this Frame object (where, when, and how you are using the paint method in your Frame object).

General diagnostic resources:

1. Inheritance Hierarchy

2. This post has a very good position on why not to use paintComponent() and to use repaint() instead. I have never been put into a situation where I have needed to forge a path with paintComponent() , however I have been in a position to use repaint() several times.

Answer 3

You are calling repaint in the game loop, but repaint does not guarantee that window will be repainted and therefore paintComponent may not be called. You should instead use paintImmediately .

paintImmediately(0, 0, 1920, 1080);