validate revalidate !!

[Anne Forumer]

I am perplexed at the behavior of the following example! I am resizing a button and see it change it's size. Perplexing thing is that validate() works but not revalidate()! repaint doesn't seem to be necessary!

Also, what do I need to do have the frame resize itself to showcomplete buttons?

There seems to be a lot of confusion about use of validate, revalidate, invalidate, paint, repaint! Is there an authoritative reference on this.

 
public class SwingTest
{
 

    public static void main (String[] args)
    {
        SwingTest st = new SwingTest();
        final JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout());
        JButton button = new JButton("Test Button");
        final JButton button2 = new JButton("Test Button2");
        button.setBorder(BorderFactory.createRaisedBevelBorder());
        panel.add(button);
        panel.add(button2);
        Insets insets = button.getInsets();
        insets = panel.getInsets();
        System.out.println(""+insets);
        insets = button.getBorder().getBorderInsets(button);
        System.out.println(""+insets);
 
        f.getContentPane().add(panel);
        f.pack();
        f.show();
        System.out.println("showed the first time");
        try
        {
            Thread.currentThread().sleep(2000);
        } catch (Exception e)
        {
            // TODO: handle exception
        }
        
        Dimension dim = new Dimension(100,100);
        Dimension dim2 = new Dimension(200,200);
        //button2.setPreferredSize(dim);
        button2.setSize(dim2);
        //this worked
        //f.pack();
        // end this worked
        button2.validate(); // <---
//        f.repaint();
 
    }
}
 

[C. Alan]

I have a tough time remembering what goes with what also. Paint and repaint deal with the graphics class, so in your example, they won't do anything.

Validate makes sure that the component has a valid layout. The API's are a little vague on invalidate, but my assumption (probably incorrect) would be that it removes the layout of the component.

Revalidate, IIRC, has to do with handling component changes due to some kind of an event...as in a button says "on", and then when you click it, it says "off", etc.

Pack resizes your window to use each components preferred size. I think if you remove your validate and repaint statements, the frame should size properly so that your components fit.

I also find it useful when I get confused to use the glossary from here:
http://mindprod.com/jgloss/

It's interesting that you used show, and not set visible. I thought show was depricated, but I just discovered that JFrame inherits the show method of the Window class which is not deprecated..

[Craig Wood]

It might be easier to see the effects if you set a size for your JFrame. If you use 'pack' you'll have to call it again to properly resize the frame after each component size change.

'revalidate' is a JComponent method and works well for swing use. I call it after any changes that may affect a Containers layout, eg, adding/removing/resizing components, changing borders or fonts. 'revalidate' will also reset scrollbars on a parent JScrollPane.

'validate' is a Component method that is overridden in Container. You can use it in swing instead of 'revalidate'. It is useful in AWT apps the way 'revalidate' is in swing.

'invalidate' is not often needed, mostly (I think) just before 'validate' to mark a (changed) component for the attention of a parent ScrollPane.

'repaint' may or may not be required after 'revalidate' or 'validate', you just have to experiment to see what is needed in each situation. I try to use the minimum required.

[Craig Wood]

About the app — 'setSize' is not so useful for resizing components in swing. 'setPreferredSize' works much better in swing and, as of j2se 1.5, is now also a Component (AWT) method. It is a luxury in gui work.

I added some things to your app as a way of exploring these validation and sizing options. 'Button 1' works with 'setPreferredSize' and 'Button 2' with 'setSize'. Observe that the 'setSize' method changes the size but not the location of button2.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class ST
{
    JButton button, button2;
    JCheckBox clear, revalidate, validate, repaint;
    JPanel panel;
 
    public ST()
    {
        button  = new JButton("Button 1");
        button2 = new JButton("Button 2");
        panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weighty = 1.0;
        gbc.gridwidth = gbc.REMAINDER;
        panel.add(button, gbc);
        panel.add(button2, gbc);
 
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(getOptions(), "North");
        f.getContentPane().add(panel);
        f.getContentPane().add(getSizingPanel(), "South");
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
 
    private JPanel getOptions()
    {
        clear = new JCheckBox("neither", true);
        revalidate = new JCheckBox("revalidate");
        validate   = new JCheckBox("validate");
        repaint    = new JCheckBox("repaint");
        ButtonGroup bg = new ButtonGroup();
        bg.add(clear);
        bg.add(revalidate);
        bg.add(validate);
        JPanel p = new JPanel();
        p.setBorder(BorderFactory.createEtchedBorder());  // functional group
        p.add(clear);
        p.add(revalidate);
        p.add(validate);
        JPanel panel = new JPanel();
        panel.add(p);
        panel.add(repaint);
        return panel;
    }
 
    private JPanel getSizingPanel()
    {
        final JRadioButton
            invalidate = new JRadioButton("invalidate"),
            setBounds  = new JRadioButton("setBounds"),
            neither    = new JRadioButton("neither", true);
        setBounds.addItemListener(new RBListener());
        ButtonGroup bg = new ButtonGroup();
        bg.add(invalidate);
        bg.add(setBounds);
        bg.add(neither);
        final SpinnerNumberModel model = new SpinnerNumberModel(75, 50, 150, 1);
        JSpinner spinner = new JSpinner(model);
        spinner.addChangeListener(new ChangeListener()
        {
            Dimension d = new Dimension();
 
            public void stateChanged(ChangeEvent e)
            {
                int value = model.getNumber().intValue();
                if(setBounds.isSelected())
                {
                    int w = panel.getWidth();
                    int h = panel.getHeight();
                    int width = value;
                    int height = value/3;
                    int x    = (w - width)/2;         // one column
                    int yInc = (h - height)/3;        // two rows
                    int y = yInc;
                    button.setBounds(x, y, width, height);
                    y += yInc;
                    button2.setBounds(x, y, width, height);
                }
                else    // layout managers
                {
                    d.width = value;
                    d.height = value/3;
                    button.setPreferredSize(d);       // swing (& AWT in j2se 1.5)
                    button2.setSize(value, value/3);  // AWT
 
                    if(invalidate.isSelected())
                    {
                        button.invalidate();
                        button2.invalidate();
                    }
                    if(revalidate.isSelected())
                    {
                        button.revalidate();
                        button2.revalidate();
                    }
                    else if(validate.isSelected())
                        panel.validate();
                }
                if(repaint.isSelected())
                    panel.repaint();
            }
        });
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = gbc.REMAINDER;
        JPanel p = new JPanel();
        p.add(new JLabel("button size"));
        p.add(spinner);
        panel.add(p, gbc);
        p = new JPanel();
        p.add(invalidate);
        p.add(setBounds);
        p.add(neither);
        panel.add(p, gbc);
        return panel;
    }
 
    private class RBListener implements ItemListener
    {
        public void itemStateChanged(ItemEvent e)
        {
            JRadioButton rb = (JRadioButton)e.getSource();
            boolean show = true;
            if(e.getStateChange() == ItemEvent.SELECTED)
                show = false;
            clear.setEnabled(show);
            revalidate.setEnabled(show);
            validate.setEnabled(show);
        }
    }
 
    public static void main (String[] args)
    {
        new ST();
    }
}

[Anne Forumer]

Thanks Craig for going through this effort to help!

I'm perplexed even more now!

 setSize 

works - and

 setPreferredSize 

doesn't if you don't check

 validate or [CODE] revalidate 

. Situation gets reversed if you

 validate 

or

 revalidate 

!

I am under the impression that

 pack 

forces everything to preferredSize.

It is good to be try out different options. Can you recommend a good reference which can help to make more sense?

[Craig Wood]

This page in the tutorial may be helpful How Layout Management Works. Otherwise, I don't know of any references to recommend. This seems to be an area best learned through practice and experimentation. Curiosity and looking at how others have put things together seem to help.