java add image to canvas

问题

I'm trying to add a image to a java canvas. I'm using the "ImageIO.read" to get the image source. The problem i'm facing is that i don't know how to display it on the canvas after reading the image location. Also later i will need to load a different image(e.g. after a button pressed) how can i do this. The update (canvas.update) method needs a "Graphics" parameter instead of an image. Below you'll find my code simplified (i left out all code that's not relevant to the canvas issue.)

public class MainWindow {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    window = new MainWindow();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public MainWindow() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        Canvas csStatusImage = new Canvas();
        csStatusImage.setBounds(393, 36, 200, 200);
        frame.getContentPane().add(csStatusImage);

        Image iMg;
        try {
            iMg = ImageIO.read(new File("Images/Error_status_1.png"));
            csStatusImage.imageUpdate(iMg, 10, 2, 2, 9, 10);
            csStatusImage.checkImage(iMg, (ImageObserver) this);
            csStatusImage.createImage((ImageProducer) iMg);

        } catch (IOException e1) {
            e1.printStackTrace();
        }
    }
}

回答1:

First of all, you going to need some way to paint the image. To achieve this, you can override the paint method of the java.awt.Canvas class

import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        Frame frame = new Frame("Testing");
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        frame.add(new ImageCanvas());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public class ImageCanvas extends Canvas {

        private BufferedImage img;

        public ImageCanvas() {
            try {
                img = ImageIO.read(new File("Images/Error_status_1.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return img == null ? new Dimension(200, 200) : new Dimension(img.getWidth(), img.getHeight());
        }

        @Override
        public void paint(Graphics g) {
            super.paint(g);
            if (img != null) {
                int x = (getWidth() - img.getWidth()) / 2;
                int y = (getHeight() - img.getHeight()) / 2;
                g.drawImage(img, x, y, this);
            }
        }

    }

}

I have to tell you, AWT is out-of-date by some 15+ years, replaced by Swing. You may find it hard to get additional support with this API. If you can, you'd better of using Swing or JavaFX

来源：https://stackoverflow.com/questions/29088318/java-add-image-to-canvas

标签

java

canvas

awt