Swing Hacks

Animate Your JList Selections #18

Chapter 2, Lists and Combos

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HACK

H A C K

#18

Animate Your JList Selections

Hack #18

Fading in and catching the eye.

Not every GUI involves windows and mouse pointers, and the visual lan-

guage of a GUI can be very different depending on what is provided by the

environment. Typically, GUIs for things like console video games and set-

top boxes don’t use a mouse metaphor, so there’s no onscreen pointer that

the user is tracking. As a result, these systems often give the user more pro-

found feedback when they move around a list—highlights slide from one

item to another, selected items fade in while deselected items fade out, etc.—

so there’s something the eye can track. You can do the same thing in Swing,

with more cell-rendering hackery. You might not need it now, but it’ll be

handy if you ever design a kiosk with Swing.

One way to show a changed selection is to show a brief animation of the cell

selection. Instead of just being highlighted instantly, you fade the selected

cell from its unselected background and foreground colors to its selected

colors over the course of a short time (really short, like a half-second, so it

isn’t annoying).

To do this, you’ll need to create an animator thread that kicks off every time

the selection changes. This short-lived thread repeatedly updates a high-

light color and calls

repaint( ). The cell renderer can then use the updated

highlight color as it redraws the cells in the list. Example 2-18 shows this

technique.

Figure 2-10. Item dropped into new position in a JList

Example 2-18. Animating the JList cell selection

import java.awt.*;

import javax.swing.*;

import javax.swing.event.*;

import java.util.*;

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Chapter 2, Lists and Combos

#18 Animate Your JList Selections

HACK

public class AnimatedJList extends JList

implements ListSelectionListener {

static java.util.Random rand = new java.util.Random( );

static Color listForeground, listBackground,

listSelectionForeground, listSelectionBackground;

static float[] foregroundComps, backgroundComps,

foregroundSelectionComps, backgroundSelectionComps;

static {

UIDefaults uid = UIManager.getLookAndFeel().getDefaults( );

listForeground = uid.getColor ("List.foreground");

listBackground = uid.getColor ("List.background");

listSelectionForeground = uid.getColor ("List.selectionForeground");

listSelectionBackground = uid.getColor ("List.selectionBackground");

foregroundComps =

listForeground.getRGBColorComponents(null);

foregroundSelectionComps =

listSelectionForeground.getRGBColorComponents(null);

backgroundComps =

listBackground.getRGBColorComponents(null);

backgroundSelectionComps =

listSelectionBackground.getRGBColorComponents(null);

}

public Color colorizedSelectionForeground,

colorizedSelectionBackground;

public static final int ANIMATION_DURATION = 1000;

public static final int ANIMATION_REFRESH = 50;

public AnimatedJList( ) {

super( );

addListSelectionListener (this);

setCellRenderer (new AnimatedCellRenderer( ));

}

public void valueChanged (ListSelectionEvent lse) {

if (! lse.getValueIsAdjusting( )) {

HashSet selections = new HashSet( );

for (int i=0; i < getModel().getSize( ); i++) {

if (getSelectionModel( ).isSelectedIndex(i))

selections.add (new Integer(i));

}

CellAnimator animator = new CellAnimator (selections.toArray( ));

animator.start( );

}

}

Example 2-18. Animating the JList cell selection (continued)

Animate Your JList Selections #18

Chapter 2, Lists and Combos

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HACK

public static void main (String[] args) {

JList list = new AnimatedJList ( );

DefaultListModel defModel = new DefaultListModel( );

list.setModel (defModel);

String[] listItems = {

"Chris", "Joshua", "Daniel", "Michael",

"Don", "Kimi", "Kelly", "Keagan"

};

Iterator it = Arrays.asList(listItems).iterator( );

while (it.hasNext( ))

defModel.addElement (it.next( ));

// show list

JScrollPane scroller =

new JScrollPane (list,

ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,

ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);

JFrame frame = new JFrame ("Checkbox JList");

frame.getContentPane( ).add (scroller);

frame.pack( );

frame.setVisible(true);

}

class CellAnimator extends Thread {

Object[] selections;

long startTime;

long stopTime;

public CellAnimator (Object[] s) {

selections = s;

}

public void run( ) {

startTime = System.currentTimeMillis( );

stopTime = startTime + ANIMATION_DURATION;

while (System.currentTimeMillis( ) < stopTime) {

colorizeSelections( );

repaint( );

try { Thread.sleep (ANIMATION_REFRESH); }

catch (InterruptedException ie) {}

}

// one more, at 100% selected color

colorizeSelections( );

repaint( );

}

// colorizeSelections( ) listing below

// AnimatedCellRenderer listing below

}

Example 2-18. Animating the JList cell selection (continued)