slight problem using JScrollPane

[Randall Twede]

i have an app that resizes the JFrame to fit the size of the image displayed in a JPanel. i decided to add a JScrollPane so it can display images that are larger than the screen(it cropped them). it works but the frame is a little too big and you cant see the horizontal scrollbar and only half of the vertical one. if i click the maximize button in the title bar, it displays correctly. how to correct this?

noticed i forgot to call super.paintComponent(g) but it worked anyway.
anyway adding that line had no effect.

[Rob Spoor]

Can you us an SSCCE?

[Randall Twede]

sure. the entire program is very short.
i know. all my variables can be private. i changed that.
sorry if its a little hard to read, i'm still mixing tabs and spaces.

/*
 * ImageViewer.java
 * Program for displaying image files
 * Created 12/2011
 */

/**
 *
 * Randall Twede
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.File;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.IOException;

public class ImageViewer extends JFrame implements ActionListener
{
    BufferedImage image;	// give DrawingArea access
    private File file;
    private JMenuBar menuBar = new JMenuBar();
    private JMenu fileMenu = new JMenu( "File" );
    private JMenuItem openMenuItem = new JMenuItem( "Open" );
    private DisplayArea displayArea = new DisplayArea();
    private final JFileChooser fc = new JFileChooser();
    JScrollPane scrollPane = new JScrollPane(displayArea);

    /** Creates a new instance of ImageViewer */
    public ImageViewer()
    {
        setTitle("ImageViewer");
        Container c = getContentPane();
        initComponents();
        setJMenuBar(menuBar);
	c.add(scrollPane);
    }

    // Improves readability of the constructor for this Class
    private void initComponents()
    {
        fileMenu.add( openMenuItem );
        openMenuItem.addActionListener(this);
        menuBar.add( fileMenu );
    }

    public void actionPerformed(ActionEvent e)
    {
        int returnVal = fc.showOpenDialog(this);
        if (returnVal == JFileChooser.APPROVE_OPTION)
        {
            try
            {
                file = fc.getSelectedFile();  
                image = ImageIO.read(file);
                if(image != null)
		{
		    image = ImageIO.read(file);
                    displayArea.repaint();
		    this.pack();
		    this.center();
		}
		else
		{
                    String message = "This program can only open image files, like gif or jpg";
                    JOptionPane.showMessageDialog( this, message, "Error",JOptionPane.ERROR_MESSAGE );
		}
            }
            catch (IOException ex)
            {
		String message = "could not open file";
		JOptionPane.showMessageDialog( this, message, "IOException",JOptionPane.ERROR_MESSAGE );          
	    }
        }
    }

    // centers a JFrame
    public void center()
    {
        this.setLocationRelativeTo(null);   
    }

    class DisplayArea extends JPanel
    {
    	public void paintComponent(Graphics g)
    	{
	    super.paintComponent(g);
            if(image != null)
	    {
		setPreferredSize(getPreferredSize());
                g.drawImage(image, 0, 0, null);
	    }
	}

	public Dimension getPreferredSize()
	{
	    if(image != null)
	    {
	    	return new Dimension(image.getWidth(),image.getHeight());
	    }
	    else
	    {
		return super.getPreferredSize();
	    }
	}
    }

    // create and display an instance of ImageViewer
    public static void main(String args[])
    {
        ImageViewer window = new ImageViewer();
	window.setSize(200, 200);
        window.center();
        window.setVisible(true);
        window.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }
}

[Rob Camick]

Not sure what pack() is doing when the preferred size is greater than the screen size, but on my system the horizontal/vertical sizes where both 12 pixels greater than the max.

I used the following to customize the size:

this.pack();

Dimension frameSize = getSize();
GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();
Rectangle screenBounds = env.getMaximumWindowBounds();

if (frameSize.width > screenBounds.width)
	frameSize.width = screenBounds.width;

if (frameSize.height > screenBounds.height)
	frameSize.height = screenBounds.height;

setSize( frameSize );

this.center();

Also, there is no need to use a custom panel to display the image. I just added a JLabel to the scrollpane and then used:

image = ImageIO.read(file);
// displayArea.repaint(); // this is never needed, the pack() will cause a repaint
ImageIcon icon = new ImageIcon(image);
label.setIcon( icon );

[Randall Twede]

ok. thanks Rob. the first code you posted looks like what i need. i used pack because sometimes the image is small. your second code is interesting as well.

that fixed it thanks

[Randall Twede]

FYI for anyone who cares. i tried Rob's suggestion about not needing to call repaint(). it worked at first(when files were different size). but when i opened files the same size(my documents/my pictures/sample pictures), pack() didn't call repaint(). in fact pack didn't get called because the size was the same. so i needed to call repaint() after all.

[Rob Camick]

If you use a JLabel and reset the Icon there is no need to call repaint() because the setIcon() method calls repaint().

[Randall Twede]

i'll try that next since it will be less code than using custom JPanel