setPreferredSize changed after the fact but GridBagLayout not updating

Question

I have a JPanel (imagePanel) that shows an image on it. I have imagePanel inside another JPanel (scrollPanel) with GridBagLayout default constraints to center it. scrollPanel is the viewport for a JScrollPane. I need to change the size of the imagePanel after the fact and still keep it centered. (The image class is one I made myself)

public class ImageView extends View {
private static final long serialVersionUID = -1745026846891845769L;

private JScrollPane scrollPane;
private JPanel scrollPanel;
public JPanel imagePanel;

public int zoom = 1;

public Image image;

public ImageView(Image image) {
    setLayout(new BorderLayout());
    setDoubleBuffered(true);

    this.image = image;

    imagePanel = new JPanel() {
        private static final long serialVersionUID = 2127374649591395224L;

        @Override
        public void paint(Graphics g) {
            super.paint(g);
            ImageView.this.image.paintImage(g, 0, 0, zoom);
        }
    };
    imagePanel.setDoubleBuffered(true);

    scrollPanel = new JPanel(new GridBagLayout());
    scrollPanel.add(imagePanel);

    scrollPane = new JScrollPane(scrollPanel);
    add(scrollPane, BorderLayout.CENTER);
}

public void zoom(int zoom) {
    if(zoom < 1) 
        this.zoom = 1;
    else
        this.zoom = zoom;

    int imageWidth = image.WIDTH * this.zoom;
    int imageHeight = image.HEIGHT * this.zoom;

    imagePanel.setPreferredSize(new Dimension(imageWidth, imageHeight));
    //What do I do here???
}

EDIT: Here is my updated code for anyone else with the same question

public class ImageView extends View {
private static final long serialVersionUID = -1745026846891845769L;

public class ImagePanel extends JPanel {
    private static final long serialVersionUID = 2127374649591395224L;

    public int zoom = 1;

    public void setZoom(int zoom) {
        if(zoom < 1) 
            this.zoom = 1;
        else
            this.zoom = zoom;
    }

    @Override
    public Dimension getPreferredSize() {
        int imageWidth = ImageView.this.image.WIDTH * this.zoom;
        int imageHeight = ImageView.this.image.HEIGHT * this.zoom;
        return new Dimension(imageWidth, imageHeight);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        ImageView.this.image.paintImage(g, 0, 0, zoom);
    }

}

private JScrollPane scrollPane;
private JPanel scrollPanel;
public ImagePanel imagePanel;

public Image image;

public ImageView(Image image) {
    setLayout(new BorderLayout());
    setDoubleBuffered(true);

    this.image = image;

    imagePanel = new ImagePanel();
    imagePanel.setDoubleBuffered(true);

    scrollPanel = new JPanel(new GridBagLayout());
    scrollPanel.add(imagePanel);

    scrollPane = new JScrollPane(scrollPanel);
    add(scrollPane, BorderLayout.CENTER);
}

public void zoom(int zoom) {
    imagePanel.setZoom(zoom);
    scrollPanel.revalidate();
    scrollPanel.repaint();
}

[Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?](http://stackoverflow.com/questions/7229226/should-i-avoid-the-use-of-setpreferredmaximumminimumsize-methods-in-java-swi) — MadProgrammer, Dec 01 '14 at 00:00

score 3 · Accepted Answer · answered Nov 30 '14 at 23:51

Don't invoke setPreferredSize().

You should override the getPreferredSize() method of your class to do the size calculation. So basically the zoom logic should be defined in that method.

Then in the zoom(..) method you invoke:

revalidate();
repaint();

The zoom() method should be part of the panel that paints the image since the zoom factor is a property of this panel. This will cause the layout manager to be invoked and your new preferred size will be used in the layout of the component.

Also, you should be overriding the paintComponent(...) method, not the paint(...) method to draw the image.

score 0 · Answer 2 · answered Nov 30 '14 at 23:44

0

According to this link: http://www.coderanch.com/t/333435/GUI/java/Whats-exact-difference-paint-repaint you may need to call validate after calling setPreferedSize

answered Nov 30 '14 at 23:44

Zack Newsham

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setPreferredSize changed after the fact but GridBagLayout not updating

2 Answers2