在Image的静态方法中，只有Image.createImage(width,height)方法创建的图片是可以修改的。本列介绍了如何在Canvas上绘制可修改的Image。
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/*--------------------------------------------------
* MutableImage.java
*
* Draw mutable image on a canvas
*
* Example from the book: Core J2ME Technology
* Copyright John W. Muchow http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class MutableImageWithCanvas extends MIDlet
{
private Display display; // The display
private ImageCanvas canvas; // Canvas
public MutableImageWithCanvas()
{
display = Display.getDisplay(this);
canvas = new ImageCanvas(this);
}
protected void startApp()
{
display.setCurrent( canvas );
}
protected void pauseApp()
{ }
protected void destroyApp( boolean unconditional )
{ }
public void exitMIDlet()
{
destroyApp(true);
notifyDestroyed();
}
}
/*--------------------------------------------------
* Class ImageCanvas
*
* Draw mutable image
*-------------------------------------------------*/
class ImageCanvas extends Canvas implements CommandListener
{
private Command cmExit; // Exit midlet
private MutableImage midlet;
private Image im = null;
private String message = "Core J2ME";
public ImageCanvas(MutableImage midlet)
{
this.midlet = midlet;
// Create exit command & listen for events
cmExit = new Command("Exit", Command.EXIT, 1);
addCommand(cmExit);
setCommandListener(this);
try
{
// Create mutable image
im = Image.createImage(80, 20);
// Get graphics object to draw onto the image
Graphics graphics = im.getGraphics();
// Specify a font face, style and size
Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_PLAIN, Font.SIZE_MEDIUM);
graphics.setFont(font);
// Draw a filled (black) rectangle
graphics.setColor(0, 0, 0);
graphics.fillRoundRect(0,0, im.getWidth()-1, im.getHeight()-1, 20, 20);
// Center text horizontally in the image. Draw text in white
graphics.setColor(255, 255, 255);
graphics.drawString(message,
(im.getWidth() / 2) - (font.stringWidth(message) / 2), 0,
Graphics.TOP | Graphics.LEFT);
}
catch (Exception e)
{
System.err.println("Error during image creation");
}
}
/*--------------------------------------------------
* Draw mutable image
*-------------------------------------------------*/
protected void paint(Graphics g)
{
// Center the image on the display
if (im != null)g.drawImage(im, getWidth() / 2, getHeight() / 2, Graphics.VCENTER
| Graphics.HCENTER);
}
public void commandAction(Command c, Displayable d)
{
if (c == cmExit)
midlet.exitMIDlet();
}
}
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