尝试在 JFrame 上绘制图像

Question

我正在尝试在 JFrame 上绘制图像，但它似乎不起作用。这是绘制图像的面板：

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import javax.swing.JPanel;
public class GraphicsPanel extends JPanel {
public BufferedImage image;
public GraphicsPanel(){
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, null);
}
}

这是JFrame：

import java.awt.Dimension;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
public class Spelplan extends javax.swing.JFrame {
public static BufferedImage image;
public static GraphicsPanel pane;
public Spelplan() {
try {
image = ImageIO.read(new File("*IMAGE PATH*"));  
}
catch(IOException e) {
System.out.println("Image not found");
}
pane = new GraphicsPanel(); 
pane.setPreferredSize(new Dimension(image.getWidth(), image.getHeight()));
pane.setVisible(true);
initComponents();
this.setPreferredSize(new Dimension(image.getWidth(), image.getHeight()));
this.add(pane);
this.pack();
pane.repaint();        
}

当程序运行时，JFrame以正确的大小显示，但没有绘制图像。知道我做错了什么吗？

Answer 1

BufferedImage image可能是公共的，但GraphicsPanel永远不会访问它。
无论如何，更好的做法是保持image私有并使用 getter 来访问它，或者将引用传递给构造函数：

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
public class Spelplan extends javax.swing.JFrame {
public static BufferedImage image;
private String imagePath = "https://upload.wikimedia.org/wikipedia/commons/3/3f/Crystal_Project_bug.png";
public Spelplan() {
try {
URL url = new URL(imagePath);
image = ImageIO.read(url);
}
catch(IOException e) {
System.out.println("Image not found");
}
add(new GraphicsPanel(image));
pack();
setVisible(true);
}
public static void main(String[] args){
new Spelplan();
}
}
class GraphicsPanel extends JPanel {
private BufferedImage image;
public GraphicsPanel(BufferedImage image){
this.image = image;
setPreferredSize(new Dimension(image.getWidth(), image.getHeight()));
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, null);
}
}

始终发布 mcve 并使用照片 url，以便其他人可以运行您的代码。