Re: cobbling a ComboBox

  To: comp.lang.java.gui
On 2008-06-25 13:07 +0100, Albretch Mueller allegedly wrote:


Do you use an IDE? If you do (and you probably should), I strongly
suggest you have a look at the library source code (of Swing, in this
case). With Netbeans, for instance, I right-click on any method or field
name and select "Go To" -> "Source" and it opens the relevant class. Why
am I telling you this? Because for your current problem, I simply opened
the source code for javax.swing.plaf.basic.BasicComboBoxUI and
javax.swing.plaf.metal.MetalComboBoxUI, looked how they did things, and
thence knew which parts I could and should interfere with. I suggest you
do the same. The library source code is, in my humble opinion, the most
valuable well of insight.

Here, I simply copy/pasted the method BasicComboBoxUI#paintCurrentValue,
and made a few modifications (no other way to do what you want to
achieve, I'm afraid).

<sscce>
package scratch;

import java.util.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.plaf.*;
import javax.swing.plaf.basic.*;
import javax.swing.plaf.metal.*;

public class Test {

     public static void main(String[] ss) throws Exception {

         UIManager.put("ComboBoxUI", "scratch.Test$CustomMetalComboBoxUI");

         UIManager.put("ComboBox.editorBackground", new
ColorUIResource(0xfff0c0c0));
         UIManager.put("ComboBox.editorForeground", new ColorUIResource(0));

         EventQueue.invokeLater( new Runnable(){
             public void run(){
                 JComboBox jcb = new JComboBox(new Object[]{"One",
"Two", "Three", "Four", "Five", "Six"});

                 System.out.println(jcb.getUI().getClass().toString());

                 jcb.setBorder( BorderFactory.createEmptyBorder(40, 60,
40, 60) );

                 JFrame f = new JFrame();
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                 f.getContentPane().add(jcb, BorderLayout.CENTER);

                 f.pack();
                 f.setLocationRelativeTo(null);

                 f.setVisible(true);
             }
         });
     }

     public static class CustomMetalComboBoxUI
     extends MetalComboBoxUI
     {
         public static ComponentUI createUI(JComponent c) {
             return new CustomMetalComboBoxUI();
         }

         @Override
         public void paintCurrentValue(Graphics g,Rectangle
bounds,boolean hasFocus) {
             ListCellRenderer renderer = comboBox.getRenderer();
             Component c;

             if ( hasFocus && !isPopupVisible(comboBox) ) {
                 c = renderer.getListCellRendererComponent( listBox,
 
comboBox.getSelectedItem(),
                                                            -1,
                                                            true,
                                                            false );
             }
             else {
                 c = renderer.getListCellRendererComponent( listBox,
 
comboBox.getSelectedItem(),
                                                            -1,
                                                            false,
                                                            false );
                 c.setBackground(UIManager.getColor("ComboBox.background"));
             }
             c.setFont(comboBox.getFont());
             if ( hasFocus && !isPopupVisible(comboBox) ) {
// c.setForeground(listBox.getSelectionForeground());
// c.setBackground(listBox.getSelectionBackground());
                 c.setForeground(
UIManager.getColor("ComboBox.editorForeground") );
                 c.setBackground(
UIManager.getColor("ComboBox.editorBackground") );
             }
             else {
                 if ( comboBox.isEnabled() ) {
                     c.setForeground(comboBox.getForeground());
                     c.setBackground(comboBox.getBackground());
                 }
                 else {
                     c.setForeground(sun.swing.DefaultLookup.getColor(
                              comboBox, this,
"ComboBox.disabledForeground", null));
                     c.setBackground(sun.swing.DefaultLookup.getColor(
                              comboBox, this,
"ComboBox.disabledBackground", null));
                 }
             }

             // Fix for 4238829: should lay out the JPanel.
             boolean shouldValidate = false;
             if (c instanceof JPanel) {
                 shouldValidate = true;
             }

             currentValuePane.paintComponent(g,c,comboBox,bounds.x,bounds.y,
                                             bounds.width,bounds.height,
shouldValidate);
         }
     }
}
</sscce>

(Note: you'll get two warnings when trying to compile this, because of
the two calls to sun.swing.DefaultLookup. I wouldn't bother about those
for the time being, but keep them in mind, as they may create problems
in future releases)


Because, as I told you, the UIManager loads the UI delegate
*reflectively*. In other words, it makes a call to Class.forName()
(essentially) with that String. So the String you put as the value must
be on the classpath. If the class "CustomMetalComboBoxUI" were not an
inner class, as I wrote it, but a class in the same package as my "Test"
class, the String ought to be "scratch.CustomMetalComboBoxUI". If it
were in another package, say package x.y.z, the String ought to be
"x.y.z.CustomMetalComboBoxUI". And so on. Google for "Java swing custom
UI delegate".

--
DF.
to reply privately, change the top-level domain
in the FROM address from "invalid" to "net"

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