java - Java图形编程绘制图像错误

Question

您好，我在将图像绘制到框架时遇到错误。我不确定这里出了什么问题。

我在这里得到以下错误。

Java: 77: cannot find symbol
symbol: variable image
location: class DrawComponent
g.drawImage(image, 0, 0, null);


class DrawComponent extends JComponent {
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        // draw a circle with the same center
        double centerX = 250;
        double centerY = 180;
        double radius = 20;

        Ellipse2D circle = new Ellipse2D.Double();
        circle.setFrameFromCenter(centerX, centerY, centerX + radius, centerY + radius);
        g2.setPaint(Color.RED);
        g2.fill(circle);
        g2.draw(circle);

        String filename = "SydneyOperaHouse.jpeg";
        try{
            Image image = ImageIO.read(new File(filename));
        }catch(IOException ex){
            // Handle Exeption
        }

        g.drawImage(image, 0, 0, null);

    }
}

任何帮助将是巨大的:)

Answer 1

几点。

解决属性范围的问题。 应当将image属性传递(或加载到)构造函数中，并存储为paint方法可见的类属性。请勿尝试使用此方法加载图像(或执行其他可能长时间运行的任务)。

在部署时，BG的图像通常将是嵌入式资源，因此可以通过URL访问它。

JComponent是ImageObserver，因此g.drawImage(image, 0, 0, null);应该是
g.drawImage(image, 0, 0, this);

我怀疑在0x0处绘制的图像应该在绘制红色椭圆之前(之前完成)，否则它将绘制在其上方。

这是一个基于悉尼图像的示例(不，不是血腥的歌剧院-挑剔，挑剔..)。

import java.awt.*;
import java.awt.geom.Ellipse2D;
import javax.swing.*;
import javax.imageio.ImageIO;
import java.net.URL;

public class DrawComponent extends JComponent {

    private Image image;

    DrawComponent(Image image) {
        this.image = image;
        Dimension d = new Dimension(image.getWidth(this),image.getHeight(this));
        this.setPreferredSize(d);
    }
    public void paintComponent(Graphics g) {
        // always call super first, to get borders etc.
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;

        // paint the BG
        g.drawImage(image, 0, 0, this);

        // draw a circle with the same center
        double centerX = 250;
        double centerY = 180;
        double radius = 20;

        Ellipse2D circle = new Ellipse2D.Double();
        circle.setFrameFromCenter(centerX, centerY, centerX + radius, centerY + radius);
        g2.setPaint(Color.RED);
        g2.fill(circle);
        g2.draw(circle);
    }

    public static void main(String[] args) throws Exception {
        String s = "http://pscode.org/media/citymorn1.jpg";
        final Image image = ImageIO.read(new URL(s));
        Runnable r = new Runnable() {
            @Override
            public void run() {
                JComponent gui = new DrawComponent(image);
                JOptionPane.showMessageDialog(null, gui);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}