We Keep Coding

more efficiently load images for JList, presumably with SwingWorker

I have a problem in which I hope SwingWorker can help me, but I am not quite sure how to integrate it in my program.
The problem:
In a CardLayout I have a button on Card1 that opens Card2.
Card2 has a JList with a custom renderer(extending JLabel) which will display on average 1 to 6 images which are:
PNGs
around 500kb in size
loaded via imageIO with the change of cards
the renderer applies heavy operations such as image scaling or blurring and than sets the image as JLabel icon.
This can almost take up to a second if around 6 images have to be rendered, which is does not happen frequently but even that occasional split second of unresponsiveness feels bad.
Now I thought a SwingWorker might help here, but I'm thoroughly confused as to how I would have to integrate it.
Assuming we had this Code snippet
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class Example {
private JPanel mainPanel = new JPanel();
private JList<Product> list = new JList();
private JScrollPane scroll = new JScrollPane();
private Map<String, Color> colorMap = new HashMap<>();
public Example() {
colorMap.put("red", Color.red);
colorMap.put("blue", Color.blue);
colorMap.put("cyan", Color.cyan);
colorMap.put("green", Color.green);
colorMap.put("yellow", Color.yellow);
mainPanel.setBackground(new Color(129, 133, 142));
scroll.setViewportView(list);
scroll.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
scroll.setPreferredSize(new Dimension(80,200));
list.setCellRenderer(new CustomRenderer());
DefaultListModel model = new DefaultListModel();
model.addElement(new Product("red"));
model.addElement(new Product("yellow"));
model.addElement(new Product("blue"));
model.addElement(new Product("red"));
model.addElement(new Product("cyan"));
list.setModel(model);
mainPanel.add(scroll);
}
public static void main(String[] args) throws IOException {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("WorkerTest");
frame.setContentPane(new Example().mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(300, 300);
frame.setMinimumSize(new Dimension(160, 255));
frame.setVisible(true);
}
});
}
class CustomRenderer extends JLabel implements ListCellRenderer<Product> {
private Product product;
public CustomRenderer() {
setOpaque(false);
}
#Override
public Component getListCellRendererComponent(JList<? extends Product> list, Product product, int index, boolean isSelected, boolean cellHasFocus) {
this.product = product;
/**
* in the actual code image is png with alpha channel respectively named to the productID of the JList object
*
* String id = product.getId();
* image = ImageIO.read(getClass().getResource("../../resources/images/" + id + ".png"));
*/
BufferedImage image1 = new BufferedImage(80, 50, BufferedImage.TYPE_INT_RGB);
BufferedImage image2 = new BufferedImage( 80, 75, BufferedImage.TYPE_INT_RGB);
Graphics g = image2.getGraphics();
/**
* this is only an example, in the actual code I might also apply gaussian blurs or rescale several time
*/
g.drawImage(image1,0,0,null);
setIcon(new ImageIcon(image2));
return this;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(colorMap.get(product.getColor()));
g.fillRect(0,0,80,75);
}
}
class Product {
String productID;
String color;
public Product(String color) {
this.color = color;
}
public String getColor() {
return color;
}
public String getProductID() {
return productID;
}
}
}
would I have to call a SwingWorker from every getListCellRendererComponent call
to take over the image operations ?
Is SwingWorker even the right tool for this problem?
any help as to how I can make this part of my GUI faster would be greatly appreciated.
EDIT:
Hovercraft Full Of Eels mentioned that preloading the images could help and that loading the images from the renderer is fundamentally wrong.
This leads me to another Question:
I have a list(let's call it list1) with around 3000 objects each object has a 8kb jpg thumbnail which is load via object ID (also during the rendering)
The list displays around 6 to 12 of these thumbnail at the same time (due to the List's Dimension)
when the user selects an object he can press a button to display Card2 from the Cardlayout mentioned in the original question and it's list(list2) with the Object
and all it's related Object in non thumbnail view (500kb png + heavy image operation). Now I think it would be feasible to preload the non thumbnail image of the Object and it's relations selected in the first list which would be around 1-6 images. If I understood correctly what Hovercraft Full Of Eels said, then I could use a SwingWorker to load these Images after the selection of an Object from list1.
But what about the around 3000 images from list1, the program seemingly is not slowed down or becomes unresponsive because they are rather small in size and there are no heavy operations on the thumbnails, but they are still load form the list1's renderer. Would it make sense to preload the several thousand thumbnails ?
btw. feel free to tell me if this kind of question edit is not wished for and if it should be made into a question of itself.

One approach might be the following:
Whenever a cell renderer component for a certain element (Product) is requested, you check whether the matching image is already loaded. If not, you start a Swing worker that does the work of loading and processing the image in the background. When the worker is done, the image is placed into a cache for later lookup. In the meantime, you let the renderer just say "Loading..." or something.
A very quick implementation is here:
And as an MCVE:
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Collections;
import java.util.Map;
import java.util.Objects;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import javax.swing.DefaultListModel;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ListCellRenderer;
import javax.swing.SwingWorker;
public class LazyImageLoadingCellRendererTest
{
private JPanel mainPanel = new JPanel();
private JList<Product> list = new JList<Product>();
private JScrollPane scroll = new JScrollPane();
public LazyImageLoadingCellRendererTest()
{
mainPanel.setBackground(new Color(129, 133, 142));
scroll.setViewportView(list);
scroll.setHorizontalScrollBarPolicy(
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
scroll.setPreferredSize(new Dimension(80, 200));
list.setCellRenderer(new LazyImageLoadingCellRenderer<Product>(list,
LazyImageLoadingCellRendererTest::loadAndProcessImage));
DefaultListModel<Product> model = new DefaultListModel<Product>();
for (int i=0; i<1000; i++)
{
model.addElement(new Product("id" + i));
}
list.setModel(model);
mainPanel.add(scroll);
}
public static void main(String[] args) throws IOException
{
EventQueue.invokeLater(new Runnable()
{
#Override
public void run()
{
JFrame frame = new JFrame("WorkerTest");
frame.setContentPane(
new LazyImageLoadingCellRendererTest().mainPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(300, 300);
frame.setMinimumSize(new Dimension(160, 255));
frame.setVisible(true);
}
});
}
private static final Random random = new Random(0);
private static BufferedImage loadAndProcessImage(Product product)
{
String id = product.getProductID();
int w = 100;
int h = 20;
BufferedImage image =
new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = image.createGraphics();
g.setColor(Color.GREEN);
g.fillRect(0, 0, w, h);
g.setColor(Color.BLACK);
g.drawString(id, 10, 16);
g.dispose();
long delay = 500 + random.nextInt(3000);
try
{
System.out.println("Load time of " + delay + " ms for " + id);
Thread.sleep(delay);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
return image;
}
class Product
{
String productID;
public Product(String productID)
{
this.productID = productID;
}
public String getProductID()
{
return productID;
}
}
}
class LazyImageLoadingCellRenderer<T> extends JLabel
implements ListCellRenderer<T>
{
private final JList<?> owner;
private final Function<? super T, ? extends BufferedImage> imageLookup;
private final Set<T> pendingImages;
private final Map<T, BufferedImage> loadedImages;
public LazyImageLoadingCellRenderer(JList<?> owner,
Function<? super T, ? extends BufferedImage> imageLookup)
{
this.owner = Objects.requireNonNull(
owner, "The owner may not be null");
this.imageLookup = Objects.requireNonNull(imageLookup,
"The imageLookup may not be null");
this.loadedImages = new ConcurrentHashMap<T, BufferedImage>();
this.pendingImages =
Collections.newSetFromMap(new ConcurrentHashMap<T, Boolean>());
setOpaque(false);
}
class ImageLoadingWorker extends SwingWorker<BufferedImage, Void>
{
private final T element;
ImageLoadingWorker(T element)
{
this.element = element;
pendingImages.add(element);
}
#Override
protected BufferedImage doInBackground() throws Exception
{
try
{
BufferedImage image = imageLookup.apply(element);
loadedImages.put(element, image);
pendingImages.remove(element);
return image;
}
catch (Exception e)
{
e.printStackTrace();
return null;
}
}
#Override
protected void done()
{
owner.repaint();
}
}
#Override
public Component getListCellRendererComponent(JList<? extends T> list,
T value, int index, boolean isSelected, boolean cellHasFocus)
{
BufferedImage image = loadedImages.get(value);
if (image == null)
{
if (!pendingImages.contains(value))
{
//System.out.println("Execute for " + value);
ImageLoadingWorker worker = new ImageLoadingWorker(value);
worker.execute();
}
setText("Loading...");
setIcon(null);
}
else
{
setText(null);
setIcon(new ImageIcon(image));
}
return this;
}
}
Note:
This is really just a quick example showing the general approach. Of course, this could be improved in many ways. Although the actual loading process is already pulled out into a Function (thus making it generically applicable for any sort of image, regardless of where it comes from), one major caveat is that: It will try to load all images. A nice extension would be to add some smartness here, and make sure that it only loads the images for which the cells are currently visible. For example, when you have a list of 1000 elements, and want to see the last 10 elements, then you should not have to wait for 990 elements to be loaded. The last elements should be priorized higher and loaded first. However, for this, a slightly larger infrastructure (mainly: an own task queue and some stronger connection to the list and its scroll pane) may be necessary. (I'll possibly tackle this one day, because it might be a nice and interesting thing to have, but until then, the example above might do it...)

would I have to call a SwingWorker from every getListCellRendererComponent call to take over the image operations ?
No, you would in fact never call a background thread from within a key rendering method. In fact this appears to be the main problem with the code above -- you're reading in images from within a rendering method, significantly reducing the perceived responsiveness of your program.
Is SwingWorker even the right tool for this problem?
Perhaps, but not where you're thinking about using it. A SwingWorker will not speed anything up, but by performing long-running tasks in the background, it would avoid blocking the Swing event thread, freezing the GUI. Best would be to read the images, once, perhaps in a SwingWorker if not done during program initiation, and save them to a variable. Do not re-read the image every time you want to render it, if this can be avoided. And again, do not read in the image from within your rendering code as this will significantly reduce the perceived responsiveness of the program.

grid layout with JPanels java

I am trying to create a program in Java that is sort of like a board game. I have gameTiles, currently with only one color as I try to get the layout right. I want the tiles to appear about halfway of the width of the window and extend to the bottom, maybe anywhere from 9x9 or 11x11 different tiles. I have tried to use the grid layout to get these to be close together, not necessarily touching but close enough to look like a board game. However, no matter what I try, the tiles are space so far apart, and change shape when I resize window. I have been using the GridLayout manager to try to achieve this. Here is my code.
import java.awt.GridLayout;
import javax.swing.JFrame;
public class GameWindow extends JFrame {
public GameWindow(String title){
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(1200,400);
}
/**
* #param args
*/
public static void main(String[] args) {
GameWindow gameWindow = new GameWindow("Game");
gameWindow.setLayout(new GridLayout(0,2));
GameTile greenTile = new GameTile(0,true,0,10);
GameTile greenTile2 = new GameTile(0,true,0,10);
gameWindow.add(greenTile);
gameWindow.add(greenTile2);
gameWindow.setVisible(true);
}
}
This is the GameWindow.java file. The GameTile.java I have so far (which is still mainly not finished just for testing) is as follows:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
/**
* #author Zachary Parks
*
*/
public class GameTile extends JPanel {
private Color color;
private Color[] colors = {Color.BLUE, Color.YELLOW, Color.BLACK};
private int score, multiplier,initialX,initialY;
private boolean positiveEffect;
public GameTile(int colorTile, boolean effect, int initX, int initY){
color = colors[colorTile];
score = getScore(color);
multiplier = getMultiplier(color);
positiveEffect = effect;
initialX = initX;
initialY = initY;
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Image image = null;
try {
image = ImageIO.read(new File("greentile.png"));
} catch (IOException e) {
e.printStackTrace();
}
g.drawImage(image,initialX,initialY,this);
}
private int getMultiplier(Color color2) {
return 0;
}
private int getScore(Color color2) {
return 0;
}
/**
* Method that returns the data from the tile in
* array of int. 0 index = added score, 1 index = tile effect score
* #return
*/
public int[] getData() {
int [] scoreData = null;
scoreData[0] = score*multiplier;
return null;
}
}
A lot of the code is still in progress, like the GameTile's properties, all I'm trying at this point is get the tiles next to each other.
This is what I am getting:

To add tiles like a grid. A tileSize variable is great to have. Let's say the image/tile is 32 pixels.
public static final tileSize = 32;
With this, we can now add tiles using a for loop:
for(int x = 0; x < SCREEN_WIDTH / GameTile.tileSize; x++) { // loop through as many tiles fit the x-axis.
for(int y = 0; y < SCREEN_HEIGHT / GameTile.tileSize; y++) { // do the same with y-axis
GameTile greenTile = new GameTile(0,true, x * GameTile.tileSize , y * GameTile.tileSize);
gameWindow.add(greenTile);
}
}
SCREEN_WIDTH and SCREEN_HEIGHT is the size of your JFrame.
Keep in mind this loops through the whole screen, you wanted the half but it's easily configurable.
Please format your code next time (tab in), much easier to read and help you.
I highly recommend moving image = ImageIO.read(new File("greentile.png")); into the constructor, right now you're loading the image every framerate for every gameTile which will cause performance drop.
Also do not have a JPanel for every GameTile. Instead keep it in your main drawing class and loop through all GameTiles using an ArrayList
public static ArrayList<GameTile> gameTiles = new ArrayList<GameTile>();
protected void paintComponent(Graphics g) {
for(int i = 0; i < gameTiles.size(); i++) {
gameTiles.get(i).draw(g);
}
So instead of adding a JPanel to the JFrame for every gameTile, we draw gameTiles at the specified coordinates. Good luck!
To answer your question in the comment field: the code will look similar to this
public class GameWindow extends JPanel {
public static ArrayList<GameTile> gameTiles = new ArrayList<GameTile>();
public static void main(String[] args) {
new GameWindow();
}
public GameWindow() {
JFrame frame = new JFrame();
frame.setSize(300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(this);
frame.setVisible(true);
// add all the tiles (I just use x and y as parameters here)
gameTiles.add(new GameTile(10, 10));
gameTiles.add(new GameTile(50, 10));
}
public void paintComponent(Graphics g) {
for(int i = 0; i < gameTiles.size(); i++) {
gameTiles.get(i).draw(g);
}
}
}
And inside your GameTile class, remove the extends JPanel. And rename the paintComponent as draw or something alike.

However, no matter what I try, the tiles are space so far apart, and change shape when I resize window
A GridLayout expands each cell to fill the space available to the component. If you only have two cells each cell will take up half the width of the frame.
So the solution is to wrap your tile panel into another panel that will respect the preferred size of the tiles. So don't set the layout of the frame, set the layout of a panel holding the tiles:
Something like:
JPanel tilePanel = new JPane( new GridLayout(0, 2, 5, 5) );
tilePanel.add( new GameTile(...) );
tilePanel.add( new GameTile(...) );
JPanel wrapper = new JPanel( new GridBagLayout() );
wrapper.add(tilePanel, new GridBagConstraints() );
frame.add(wrapper, BorderLayout.CENTER );
The above code will cause the tiles to be centered in the frame.
frame.add(wrapper, BorderLayout.LINE_END);
The above will cause the tiles to display on the right of the frame vertically centered.

Components in JList are Hidden by White Square Thing Until Clicked

In a project I've been working on, I noticed that all the JList items in my JScrollPane are hidden until the JScrollPane/JList has been clicked. The weird part is it's not completely covered. There's this white box with a transparent border that spreads out over the whole thing, covering all but a few pixels on all edges.
Pictures:
As you can see, there is this white block in the middle - notice the pink "border":
Now, once I click that white box, it goes away:
I know the magenta looks horrible, but I'm using it for contrast.
Which leads me to my question: how do I get rid of that obnoxious white box?
Here is my code:
public static void listJars(File f)
{
JCheckBox firstBox = null;
DefaultListModel<JCheckBox> model = new DefaultListModel<>();
if(mainGUI.checkList != null)
{
//System.out.println("Already exists lol: " + mainGUI.checkList.getName());
mainGUI.pluginList.remove(mainGUI.checkList);
}
//mainGUI.pluginList.repaint();
File[] files = new File(f.getPath()).listFiles();
if (files != null)
{
for (File file : files)
{
if (file.getName().endsWith(".jar") || file.getName().endsWith("._jar"))
{
JCheckBox cb = new JCheckBox(file.getName());
if(firstBox == null)
{
firstBox = cb;
}
cb.setSelected(file.getName().endsWith(".jar"));
cb.setVisible(true);
cb.setText(file.getName());
model.addElement(cb);
cb.repaint();
}
}
}
JCheckBoxList jCheckBoxList = new JCheckBoxList(model, mainGUI.textField1.getText());
jCheckBoxList.setName("pluginCheckboxList");
jCheckBoxList.setSize(mainGUI.pluginList.getSize());
mainGUI.pluginList.add(jCheckBoxList);
mainGUI.checkList = jCheckBoxList;
jCheckBoxList.setVisible(true);
jCheckBoxList.setVisibleRowCount(10);
}
And ten there's my JCheckBoxList class.
package Components;
import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.File;
#SuppressWarnings("serial")
public class JCheckBoxList extends JList<JCheckBox>
{
protected static Border noFocusBorder = new EmptyBorder(1, 1, 1, 1);
protected String lastPath;
public JCheckBoxList(final String lastPath)
{
this.lastPath = lastPath;
setCellRenderer(new CellRenderer());
setBackground(Color.magenta);
addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent e)
{
int index = locationToIndex(e.getPoint());
if (index != -1)
{
JCheckBox checkBox = getModel().getElementAt(index);
checkBox.setSelected(!checkBox.isSelected());
repaint();
final String oldname = checkBox.getText();
if (!checkBox.isSelected())
{
checkBox.setName(checkBox.getText().substring(0, checkBox.getText().length() - 4) + "._jar");
}
else
{
checkBox.setName(checkBox.getText().substring(0, checkBox.getText().length() - 5) + ".jar");
}
System.out.println("Changed! Sel: " + checkBox.isSelected() + ", Name: " + checkBox.getName());
checkBox.setText(checkBox.getName());
String base = new File(lastPath).getParent() + "/plugins/";
boolean rename = new File(base + oldname).renameTo(new File(base + checkBox.getText()));
}
}
});
setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
public JCheckBoxList(ListModel<JCheckBox> model, String lastPath)
{
this(lastPath);
setModel(model);
}
protected class CellRenderer implements ListCellRenderer<JCheckBox>
{
public Component getListCellRendererComponent(
JList<? extends JCheckBox> list, JCheckBox value, int index,
boolean isSelected, boolean cellHasFocus)
{
//Drawing checkbox, change the appearance here
value.setBackground(isSelected ? getSelectionBackground()
: getBackground());
value.setForeground(isSelected ? getSelectionForeground()
: getForeground());
value.setEnabled(isEnabled());
value.setFont(getFont());
value.setFocusPainted(false);
value.setBorderPainted(true);
value.setBorder(BorderFactory.createEmptyBorder(0, 10, 5, 0));
return value;
}
}
}
And then there's my scroll pane, which has these settings (using the Intelliji IDEA UI designer):
Any ideas?

mainGUI.pluginList.add(jCheckBoxList);
mainGUI.checkList = jCheckBoxList;
jCheckBoxList.setVisible(true);
jCheckBoxList.setVisibleRowCount(10);
Looks to me like you are dynamically adding components to a visible GUI.
When you do this the basic code is:
panel.add(...);
panel.revalidate();
panel.repaint();
You should set the visibleRowCount() before the above code is executed.
Also:
Swing components are visible by default so you don't need the setVisible(true).
You may want to consider using a one column JTable since it already supports a checkbox renderer and editor.
Edit:
The solution I gave you above is the general solution. A scroll pane is different, you should only ever add a component to the viewport.
Based on your incorrect solution you should be using:
//mainGUI.pluginList.add(jCheckBoxList);
mainGUI.pluginList.setViewportView(jCheckBoxList);
The problem with posting only a few random lines of code is that we don't know the full context of the code. I did not realize "pluginList" was actually a scrollpane. Usually the variable name will have scroll or scrollpane in the name.

mainGUI.pluginList.setViewportView(mainGUI.checkList); // pluginList is the JScrollPane.
Do that, and it fixes everything! Put it in with my listJars method.

Java Swing countrycombobox with icons

I hope someone can help me out. Iam trying to create a "countrycombobox" with icons in Java Swing. I found some stuff, but nothing did work for me. Maybe the problem is, that Iam still "new" to Java.
I just want it simple like this: http://www.zomex.com/libs/images/layout/whmcs-template-language-select-w-flags-eco.jpg
Just the flags in front of the countrys.
I would really appreciate a working example. I really wonder, that there is no standard option or a good code snippet(used Google a lot to find help here) for stuff like this.

I found a better example and wanna share my stuff with you. There is just one problem left, that I dont get it sized.
package view;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CountryComboBox extends JPanel {
ImageIcon[] images;
String[] imgStrings = {"de"};
/*
* Despite its use of EmptyBorder, this panel makes a fine content
* pane because the empty border just increases the panel's size
* and is "painted" on top of the panel's normal background. In
* other words, the JPanel fills its entire background if it's
* opaque (which it is by default); adding a border doesn't change
* that.
*/
public CountryComboBox() {
super(new BorderLayout());
//Load the images and create an array of indexes.
images = new ImageIcon[imgStrings.length];
Integer[] intArray = new Integer[imgStrings.length];
for (int i = 0; i < imgStrings.length; i++) {
intArray[i] = new Integer(i);
images[i] = createImageIcon("/res/" + imgStrings[i] + ".png");
if (images[i] != null) {
images[i].setDescription(imgStrings[i]);
}
}
//Create the combo box.
JComboBox imgList = new JComboBox(intArray);
ComboBoxRenderer renderer= new ComboBoxRenderer();
imgList.setRenderer(renderer);
imgList.setMaximumRowCount(3);
//Lay out the demo.
add(imgList, BorderLayout.PAGE_START);
//setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
}
/** Returns an ImageIcon, or null if the path was invalid. */
protected static ImageIcon createImageIcon(String path) {
java.net.URL imgURL = CountryComboBox.class.getResource(path);
if (imgURL != null) {
return new ImageIcon(imgURL);
} else {
System.err.println("Couldn't find file: " + path);
return null;
}
}
class ComboBoxRenderer extends JLabel
implements ListCellRenderer {
private Font uhOhFont;
public ComboBoxRenderer() {
setOpaque(true);
setHorizontalAlignment(CENTER);
setVerticalAlignment(CENTER);
}
/*
* This method finds the image and text corresponding
* to the selected value and returns the label, set up
* to display the text and image.
*/
#Override
public Component getListCellRendererComponent(
JList list,
Object value,
int index,
boolean isSelected,
boolean cellHasFocus) {
//Get the selected index. (The index param isn't
//always valid, so just use the value.)
int selectedIndex = ((Integer)value).intValue();
if (isSelected) {
setBackground(list.getSelectionBackground());
setForeground(list.getSelectionForeground());
} else {
setBackground(list.getBackground());
setForeground(list.getForeground());
}
//Set the icon and text. If icon was null, say so.
ImageIcon icon = images[selectedIndex];
String img = imgStrings[selectedIndex];
setIcon(icon);
if (icon != null) {
setText(img);
setFont(list.getFont());
} else {
setUhOhText(img + " (no image available)",
list.getFont());
}
return this;
}
//Set the font and text when no image was found.
protected void setUhOhText(String uhOhText, Font normalFont) {
if (uhOhFont == null) { //lazily create this font
uhOhFont = normalFont.deriveFont(Font.ITALIC);
}
setFont(uhOhFont);
setText(uhOhText);
}
}
}
I call it in a JPanel with absolute layout:
JComponent newContentPane = new CountryComboBox();
newContentPane.setOpaque(true); //content panes must be opaque
newContentPane.setBounds(10, 75, 50, 26);
contentPane.add(newContentPane);
setBounds isnt working, just to get the right position. I cant size it with this.
Best regards
Acanis

Why does a fireContentsChanged call of a JList freezes the entire GUI?

I had some problems with freezing SWING GUIs when re-rendering a JTable with a custom cell renderer in Java. So I asked the question "Why does a JTable view update block the entire GUI?". The answers pointed to the fact, that a JList without modifying JTable and overwriting doLayout might be a better choice. So I implemented the example with a JList and ran into the same problem: while generating data, everything works fine and the progress bar moves. But when the view is updated, the program freezes and the progress bar stops moving.
Please note, that the sleep statement is there only to let the generation take a longer, more realistic time (reading thousands of data sets via JDBC and create objects out of them takes a lot time). One could remove it and increment the number of generated items. But you can clearly see, that the HTML rendering is quite slow. But I need this colors and the two lines (if not necessarily so many different colors).
So could you please tell me, where my mistake is? I think, that EDT and other work is separated through separate threads and I cannot see any mistke.
Update: I looked around at SO and found this question "https://stackoverflow.com/a/20813122/2429611". There is said:
The more interesting question would be how to avoid that UI blocking, but I don't think that's possible with just Swing, you'll have to implement some lazy loading, or rendering in batches.
This would mean, that I cannot solve my problem. Is this correct?
package example;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.AbstractListModel;
import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.ListCellRenderer;
import javax.swing.SwingUtilities;
public class ListExample extends AbstractListModel {
static List<DemoObject> internalList = new ArrayList<>();
#Override
public int getSize() {
return internalList.size();
}
#Override
public DemoObject getElementAt(int index) {
return internalList.get(index);
}
public void fireContentsChanged() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
fireContentsChanged(this, 0, -1);
}
});
}
static class MyCellRenderer extends JLabel implements ListCellRenderer<ListExample.DemoObject> {
public MyCellRenderer() {
setOpaque(true);
}
#Override
public Component getListCellRendererComponent(JList<? extends ListExample.DemoObject> list,
ListExample.DemoObject value,
int index,
boolean isSelected,
boolean cellHasFocus) {
setText("<html>" + value.toString()
+ "<br/>"
+ "<span bgcolor=\"#ff0000\">Line 2; Color = " + value.c + "</span>");
Color background;
Color foreground;
// check if this cell represents the current DnD drop location
JList.DropLocation dropLocation = list.getDropLocation();
if (dropLocation != null
&& !dropLocation.isInsert()
&& dropLocation.getIndex() == index) {
background = Color.BLUE;
foreground = Color.WHITE;
// check if this cell is selected
} else if (isSelected) {
background = Color.RED;
foreground = Color.WHITE;
// unselected, and not the DnD drop location
} else {
background = value.c; //Color.WHITE;
foreground = Color.BLACK;
};
setBackground(background);
setForeground(foreground);
return this;
}
}
static class DemoObject {
String str;
Color c;
public DemoObject(String str, int color) {
this.str = str;
this.c = new Color(color);
}
#Override
public String toString() {
return str;
}
}
static JPanel overlay;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("Example");
frame.setLayout(new BorderLayout(4, 4));
// Add JTable
final ListExample model = new ListExample();
JList list = new JList(model);
list.setCellRenderer(new MyCellRenderer());
frame.add(new JScrollPane(list), BorderLayout.CENTER);
// Add button
Box hBox = Box.createHorizontalBox();
hBox.add(new JButton(new AbstractAction("Load data") {
#Override
public void actionPerformed(ActionEvent e) {
new Thread(new Runnable() {
#Override
public void run() {
overlay.setVisible(true);
internalList.clear();
System.out.println("Generating data ...");
SecureRandom sr = new SecureRandom();
for (int i = 0; i < 10000; i++) {
internalList.add(
new DemoObject(
"String: " + i + " (" + sr.nextFloat() + ")",
sr.nextInt(0xffffff)
)
);
// To create the illusion, that data are
// fetched via JDBC (which takes a little
// while), this sleep statement is embedded
// here. In a real world scenario, this wait
// time is caused by talking to the database
// via network
if (i%10 == 0) {
try {
Thread.sleep(1);
} catch (Exception e) {
}
}
}
System.out.println("Updating view ...");
model.fireContentsChanged();
overlay.setVisible(false);
System.out.println("Finished.");
}
}).start();
}
}));
hBox.add(Box.createHorizontalGlue());
frame.add(hBox, BorderLayout.NORTH);
// Create loading overlay
overlay = new JPanel(new FlowLayout(FlowLayout.CENTER)) {
#Override
protected void paintComponent(Graphics g) {
g.setColor(new Color(0, 0, 0, 125));
g.fillRect(0, 0, getWidth(), getHeight());
super.paintComponent(g);
}
};
overlay.setOpaque(false);
overlay.setBackground(new Color(0, 0, 0, 125));
JProgressBar bar = new JProgressBar();
bar.setIndeterminate(true);
overlay.add(bar);
frame.setGlassPane(overlay);
frame.getGlassPane().setVisible(false);
// Create frame
frame.setSize(600, 400);
frame.setVisible(true);
}
});
}
}

there are three problems (recreating, reseting the model, and custom Renderer stoped to works)
JList (JComboBox hasn't) has an issue by removing more than 999 items, you have to set a new model to JList
see important for ComboBoxModel extends AbstractListModel implements MutableComboBoxModel for setElementAt(to hold current selection)
usage of public void fireContentsChanged() { is wrong, don't see reason to use this way, again is about to replace current, reset the model
. e.g. with success atr runtime and by recrusive testing for/if event (fired)
setModel(new DefaultListModel(list.toArray()) {
protected void fireContentsChanged(Object obj, int i, int j) {
if (!isFired)
super.fireContentsChanged(obj, i, j);
}
});