如何从主要访问重绘？

Question

I am working on a Java program that basically renders an image from a file source and then paints that image onto a panel (which is on a frame).

Now what I am able to do is invoke a line of code of the form

printpanel.getGraphics().drawImage(myimage.globalimage, 0,0, null);

where myimage is a class that contains the image.

As many of you know, this only prints the image 1 time, and should I resize the frame, the image disappears.

Now the way to fix this would be to put the line into the repaint method, but i'm in the main method right now so how do I access the definition of the repaint method and change it from within the main method?

Thanks!

=====================================================================================================

My code:

MAIN CLASS:

    package imagetester;
import java.awt.image.*;
import javax.swing.*;
import javax.imageio.*;
import java.awt.Graphics2D.*;
import java.io.*;

public class Imagetester 
{



    public static void main(String[] args) 
    {
        JFrame printframe = new JFrame("The drawing frame");
        JPanel printpanel = new JPanel();
        printframe.setSize(700,700);
        printpanel.setSize(700,700);
        printframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        printframe.add(printpanel);
        printpanel.setVisible(true);
        printframe.setVisible(true);

        Imageobject myimage = new Imageobject();
        try
        {
            myimage.setImage("word.jpg");
        }
        catch(IOException e)
        {
            System.out.println("the image failed!");
        }


        printpanel.getGraphics().drawImage(myimage.globalimage, 0,0, null);
        printpanel.repaint();


        System.out.println("hi");

    }

}

myimage class:

    package imagetester;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class Imageobject 
{
    BufferedImage globalimage;

    public void setImage(String filename) throws IOException
    {
        globalimage = ImageIO.read(new File(filename));

    }

    public void Imagebject()
    {

    }
}

Answer 1

I'm not sure I understand fully, but if what you want to do is display a panel with an image inside a window, you should subclass JPanel (or whatever other panel you'd like), and override the paintComponent method to paint the image. Something along the lines of:

public class ImagePanel extends JPanel {
    private Image image;

    public ImagePanel(Image image) {
        this.image = image;
    }

    @Override
    protected void paintComponent(graphics g) {
        g.drawImage(image, 0, 0, this);
    }
}

Answer 2

Now what i am able to do is invoke a line of code of the form printpanel.getGraphics().drawImage(myimage.globalimage, 0,0, null);

No don't do that. Your printPanel should already have it's paintComponent method, with the a drawImage in it.

Image image;
...
@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (image != null) {
        g.drawImage(image, ..., this); // this is the ImageObserver. Should not be null
    }
}

Then you can just have a setter for it if you want to change it

public void setImage(Image image) {
    this.image = image;
    repaint();
}

Just call that method with the image you want to change

---

EDIT

There's no way around it. You need to @Override the paintComponent method of the JPanel . When you resize the frame, repaint() will automatically be called, leaving the image there. The image should be drawn in the paintComponent method. You can have the panel's constructor take an Image argument if you want to instantiate that way, with the image from the ImageObject

Answer 3

As many of you know, this only prints the image 1 time, and should I resize the frame, the image disappears.

What is your requirement when the frame resizes?

1. Do you paint the image at its original size? If so then just use a JLabel with an ImageIcon and add the label to the frame
2. Do you want the image to scale with the size of the frame? Then you need to do custom painting. You can create a custom component as demonstrated in other answers. Or you can use a JLabel with a Stretch Icon which will stretch to fill the space available to the label.