图片不会在Java中绘制

Question

So I'm trying to draw an image onto a JFrame and I'm using the defualt toolkit as an image observer but every time I run the project it doesn't draw the image, however it will draw and move (succesfully) other shapes that I test.

private class Painter extends JPanel implements ImageObserver {

@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    Toolkit tk = Toolkit.getDefaultToolkit();
    Image player = tk.createImage("player.jpg");
    tk.prepareImage(player, 50, 50, rootPane);        
    g.setColor(Color.red);
   // g.drawRect(x, y, 50, 50); 
    g.drawImage(player, 200, 200, this);
    window.repaint();            
    }
}

Answer 1

Your paintComponent method should do nothing bur paint.

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

        g.setColor(Color.red);
        // g.drawRect(x, y, 50, 50);
        g.drawImage(player, 200, 200, this);
    }

The toolkit and image lines need to be in the Painter constructor. Class names should start with a capital letter.

Edit based on the comment:

You write code that looks like this:

private Image player;

public Painter() throws Exception {
    player = ImageIO.read(getClass().getResource("player.jpg"));
}

The player.jpg needs to be in the same directory as the source code. Otherwise, your image directory needs to be in the classpath of your Java application.

Here's a complete, simple Swing application to draw an image on a JPanel.

package com.ggl.testing;

import java.awt.Graphics;
import java.awt.Image;
import java.io.IOException;

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

public class MyPanel extends JPanel {

    private static final long serialVersionUID = -9008812738915944216L;

    private static JFrame frame;
    private static MyPanel panel;
    private static Image image;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                image = getImage();
                frame = new JFrame();
                panel = new MyPanel();
                frame.setSize(500, 500);
                frame.add(panel);
                frame.setVisible(true);
            }
        });
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(image, 100, 100, MyPanel.this);
    }

    private static Image getImage() {
        Image image = null;
        try {
            image = ImageIO.read(MyPanel.class.getResource("maze.jpg"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return image;
    }
}

Change maze.jpg to your image, and put the image in the same directory as this example code.

Answer 2

1. Don't do I/O in a painting method. Painting methods are for painting only.
2. Don't invoke repaint() in a painting method. This will cause an infinite loop.

Read the image into a variable of your class in the constructor of your class using ImageIO so the image is available when it is time to paint the image. ImageIO will generate a message if the image is not found.

Answer 3

The final code looks like this for anyone who's interested. The action listener wasn't included, earlier, because it was mostly irrelevant to the question. The reason the last snippet was included, the public painting, was because the action listener couldn't be called from inside the static main method. This subclass was originally what contained all the window.* lines but was causing an infinite # of created windows so while that was moved to the main the new painting call had to be encased in a controlled loop and external from the main method. Speical Thanks to all those who helped me with this, especially Gilbert Le Blanc

package painting;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.*;
import java.io.*;
import javax.imageio.ImageIO;


/**
 *
 * @author tt700
 */
public class Painting extends JPanel {
    // declaring variables that control movement, show the frame, and make the picture
    int x =50, y =50, counter = 0;
    private static JFrame window = new JFrame("Paint a Picture");
    private static Painting canvas;
    private static Image player;


// main method
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable(){
    @Override
    public void run(){    
    JLabel title = new JLabel("Making a picture frame");
    window.add(title, BorderLayout.NORTH);
    canvas = new Painting();
    window.add(canvas);
    player = getImage("player.jpg");
    window.setVisible(true);
    window.setSize(300,300);
    window.setForeground(Color.red);

    }
   });
}

@Override
// the method that does all the painting
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(player, x, y, Painting.this);
}

// the method that gets a desired image and makes it displayable, with arguments it can be used to swap pictures easily
private static Image getImage(String imagePath){
    Image player = null;
 try{
    player = ImageIO.read(Painting.class.getResource(imagePath));
        }catch(IOException e){
            e.printStackTrace();
        }
      return player; 
}
// the class that controls movement of the picture
public class movement implements KeyListener{   

    @Override
    public void keyTyped(KeyEvent e) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }

    @Override
    // the method that listens to which keys are pressed and acts accordingly
    public void keyPressed(KeyEvent e) {
        if(e.getKeyCode() == KeyEvent.VK_RIGHT){                
        x += 5;                
        window.repaint();
    }
    else if(e.getKeyCode() == KeyEvent.VK_LEFT){
        x -= 5;
        window.repaint();
    }
    else if(e.getKeyCode() == KeyEvent.VK_UP){
        y -= 5;
        window.repaint();
    }
    else if(e.getKeyCode() == KeyEvent.VK_DOWN){
        y += 5;
        window.repaint();
    }
    }

    @Override
    public void keyReleased(KeyEvent e) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }       
}

// the subclass that adds a key listener to the proper component, created since action listeners can't be called in static methods (main)
public Painting(){
    do{
    counter = 1;
    window.addKeyListener(new movement());
    }while(counter < 1);
}

}