GUI Tutorial
Post on 30-Dec-2015
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GUI Tutorial
Images
Images
Useful Info – not on final exam
Images and Icons Image class
Abstract class – why? Superclass of all graphical image classes
Icon interface Represents a fixed-sized picture Methods getIconHeight, getIconWidth, paintIcon Can be used to decorate buttons, labels, tabbed
panes ImageIcon class
Implementation of the Icon interface Creates an icon from a GIF, JPEG, or PNG image.
*
Where’s the image? Common issue: Eclipse must be able to find the
images For compatibility with jar files, store under src How can Eclipse find the image?
1. Create images folder under the [Project]/src2. Drag your file into Eclipse (DO NOT just copy in
Windows, Eclipse won’t know about it.)
Need to find the imageURL url = getClass().getResource("/images/sm_crazybird.gif");
URL = uniform resource locator getClass() returns a Class object. Stores details about the class, such
as methods, fields etc. getResource(String) finds a resource with a given name. First creates
absolute name of resource. If the String begins with ‘/’, absolute name is String (minus the ‘/’). Otherwise, the package name is appended to the front. In the package name, . are converted to ‘/’ (e.g. package one.two.three would be one/two/three. Important in order to match directory structure.
Toolkit - abstract superclass of all actual implementations of the Abstract Window Toolkit. Subclasses of Toolkit are used to bind the various components to particular native toolkit implementations.
Toolkit.getDefaultToolkit() – gets appropriate toolkit for this platform Toolkit.getDefaultToolkit().getImage(url) – reads gif, png or jpg pixel
data, creates an Image
Potential Issue Images have to be loaded from disk, can take
time Might have code to draw image on JPanel, but
image isn’t loaded when app displays Solution: MediaTracker
Create a MediaTracker object Add image(s) Wait for image(s) to load Must use try/catch, in case process is interrupted
Put it in codepublic class ImagePanel extends JPanel {
private Image thumbnail;
public ImagePanel() {
MediaTracker tracker = new MediaTracker(this);
URL url = getClass().getResource("/images/crazy_cat.gif");
Image original = Toolkit.getDefaultToolkit().getImage(url);
tracker.addImage(original, 0);
try {
tracker.waitForID(0);
} catch (InterruptedException e) { return; }
thumbnail = original.getScaledInstance(64, 64, Image.SCALE_FAST);
}
public void paintComponent(Graphics g) {
int PADDING = 20;
g.drawImage(thumbnail, PADDING, PADDING, 64, 64, null);
}
}
CHANGE image name as needed
Images and Buttonspublic class ButtonPanel extends JPanel {
private JButton myButton;
private ImageIcon myImage;
public ButtonPanel() {
myButton = new JButton();
URL url = getClass().getResource("/images/crazycat.gif");
myImage = new ImageIcon(Toolkit.getDefaultToolkit().getImage(url));
myButton.setIcon(myImage);
add(myButton);
}
}
Put it all togetherpublic class ImageFrame extends JFrame {
public ImageFrame() {
setTitle("Image Play");
setSize(180, 250);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ImagePanel imagePanel = new ImagePanel();
add(imagePanel, BorderLayout.CENTER);
ButtonPanel buttonPanel = new ButtonPanel();
add(buttonPanel, BorderLayout.SOUTH);
}
public static void main(String[] args) {
// Puts GUI on regular event queue, will update as soon as possible
SwingUtilities.invokeLater(new Runnable() {
public void run() {
ImageFrame frame = new ImageFrame();
frame.setVisible(true);
} });
}
}
Quick Info: Threads Threads are covered in detail in CSCI400 and CSCI442 For now, it’s good to know that there are potentially 3
threads: Initial threads, the threads that execute initial application
code. The main method runs in this thread The event dispatch thread, where all event-handling code
is executed. Most code that interacts with the Swing framework must also execute on this thread.
Worker threads, also known as background threads, where time-consuming background tasks are executed. We won’t deal with these.
http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html
Correct way to start a GUIpublic static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
ImageFrame frame = new ImageFrame();
frame.setVisible(true);
}
});
}
http://javarevisited.blogspot.com/2011/09/invokeandwait-invokelater-swing-example.htmlhttp://www.javamex.com/tutorials/threads/invokelater.shtmlhttp://www2.sys-con.com/itsg/virtualcd/Java/archives/0605/ford/index.html
More Images
Draw on a panel, MediaTracker
MediaTracker Images that are created from a URL,
filename or byte array are preloaded using MediaTracker to monitor the loaded state of the image.
You can also draw imagesimport javax.swing.*;
import java.net.*;
import java.awt.*;
public class ImagePanel extends JPanel {
private Image original;
private MediaTracker tracker;
public static final int PADDING = 20;
public ImagePanel()
{
tracker = new MediaTracker(this);
original = getImage("/images/crazycat.gif");
tracker.addImage(original, 0);
try {
tracker.waitForID(0);
} catch (InterruptedException e) {
return;
}
}
Use MediaTracker to control timing – without this, the panel may display before the image is loaded.
Drawing images, continuedpublic void paintComponent(Graphics g) {
g.drawImage(original, PADDING, PADDING, 64, 64, null);
}
private Image getImage(String pathName) {
URL url = getClass().getResource(pathName);
Image image = Toolkit.getDefaultToolkit().getImage(url);
return image;
}
public static void main(String[] args) {
JFrame frame = new JFrame("Image Play");
ImagePanel panel = new ImagePanel();
frame.add(panel);
frame.setSize(200, 200);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
Advanced Topics
Image in a jar
Jar File In Eclipse, highlight project Right-click, Export, Jar. Pick location for jar file On the last dialog, identify the class
containing main
Complete program for reference - Image
import java.awt.*;
import javax.swing.*;
import java.net.*;
public class ImageGUI extends JPanel {
private ImageIcon myImage;
public ImageGUI()
{
JButton button = new JButton();
add(button);
myImage = new ImageIcon(getImage("/images/crazycat.gif"));
Image original = myImage.getImage();
button.setIcon(myImage);
}
public Image getImage(String pathName)
{
URL url = getClass().getResource(pathName);
Image image = Toolkit.getDefaultToolkit().getImage(url);
return image;
}
public static void main(String[] args) {
JFrame frame = new JFrame("Image Play");
ImageGUI panel = new ImageGUI();
frame.add(panel, BorderLayout.CENTER);
frame.setSize(200, 200);
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
} // end of class
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