Re: Odd behaviour or normal?

From:
"John B. Matthews" <nospam@nospam.invalid>
Newsgroups:
comp.lang.java.gui
Date:
Fri, 04 Jun 2010 14:32:34 -0400
Message-ID:
<nospam-3E95D1.14323404062010@news.aioe.org>
In article <hub7nc$n9r$1@speranza.aioe.org>,
 "Rhino" <no.offline.contact.please@example.com> wrote:

I'd like to be clear on whether extending JPanel is or is NOT a
reasonable thing.


Extending JPanel is reasonable if you're changing the panel's behavior.
Containment using composition is a way to add other JComponents to a
JPanel. In this example, ImagePanel _contains_ a button and some text,
and it _extends_ JPanel to add the ability to draw a background image.

class ImagePanel extends JPanel {

    BufferedImage img;
    JButton button = new JButton();
    JTextField text = new JTextField();

    ImagePanel(String name) {
        super(true);
        button.setText(name);
        this.add(button);
        text.setText(name);
        this.add(text);
        this.setToolTipText(name);
        try {
            img = ImageIO.read(new File(name));
            this.setPreferredSize(new Dimension(
                img.getWidth(), img.getHeight()));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), null);
    }
}

There were inevitably problems in getting the labels to line up
properly with the text fields when I had the labels in one JPanel and
the text fields, spinners, etc. on a different JPanel.


This is controlled by the container's layout manager. Nesting JPanels is
one way to achieve a desired effect:

<http://java.sun.com/docs/books/tutorial/uiswing/layout/index.html>

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

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