animation.java

Sun公司的J2ME官方例程若干

/*
 * @(#)Animation.java	1.5 01/04/04
 *
 * Copyright (c) 2000-2001 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information"). You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 */

package examples.photoalbum;

import java.io.IOException;
import java.util.Vector;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.Graphics;

/**
 * An Animation contains the set of images to display.
 * Images are read from resource files supplied in the
 * JAR file.
 * <p> 
 * This implementation keeps the Images in the heap.
 * If memory is short, a more deliberate management
 * of Image may be required.
 */
class Animation {

	/** 
	 * Location to draw the animation, set these fields to
	 * change the location where the image is drawn.
	 */
	int x, y;

	/**
	 * The width and the height of the images (max of all if they
	 * are different).
	 * They are set when images are loaded and should not be changed.
	 */
	int width, height;

	/**
	 * Vector of images in the sequence.
	 */
	private Vector images;

	/**
	 * Current index into the sequence of images.
	 */
	private int index;

	/**
	 * Size of sequence of images.
	 * Set to a large number until the last image of
	 * the sequence has been read.
	 */
	private int size;

	/**
	 * Prefix or name of the image.
	 */
	private String prefix;

	/**
	 * Create a new Animation.
	 */
	Animation() {
		images = new Vector(30);
	}

	/**
	 * Advance to the next image.
	 * If the number of images is known then just advance
	 * and wrap around if necessary.
	 * If the number of images is not known then when 
	 * advancing off the end of the known images try to
	 * create a new image using the pattern.
	 * When an attempt fails that sets the number of images.
	 */
	void next() {
		int nextindex = index + 1;
		if (nextindex >= size) {
			index = 0;
		} else if (nextindex >= images.size()) {
			// Try to read the next image
			// If that works put it into the images vector
			try {
				String name = prefix + nextindex + ".png";
				Image image = Image.createImage(name);
				images.setSize(nextindex+1);
				images.setElementAt(image, nextindex);
				index = nextindex;
			} catch (IOException ex) {
				// No more images, set the size of the sequence.
				size = nextindex;
				index = 0;
			} catch (Exception e) {
				size = nextindex;
				index = 0;
			}
		} else {
			// Index is within range of Images already read
			index = nextindex;
		}
	}

	/**
	 * Back up to the previous image.
	 * Wrap around to the end if at the beginning.
	 */
	void previous() {
		index--;
		if (index < 0) {
			index = images.size()-1;
		}
	}

	/**
	 * Paint the current image in the sequence.
	 * The image is drawn to the target graphics context
	 * at the x, and y of the Animation.
	 * @param g graphics context to which the next image is drawn.
	 */
	public void paint(Graphics g) {
		if (images.size() > 0) {
			g.drawImage((Image)images.elementAt(index), x, y, 0);
		}
	}

	/**
	 * Load Images from resource files using 
	 * <code>Image.createImage</code>.
	 * The first image is loaded to determine whether it is a
	 * single image or a sequence of images and to make sure it exists.
	 * Subsequent images are loaded on demand when they are needed.
	 * If the name given is the complete name of the image then
	 * it is a singleton.
	 * Otherwise it is assumed to be a sequence of images 
	 * with the name as a prefix. Sequence numbers (n) are
	 * 0, 1, 2, 3, .... The full resource name is the concatenation
	 * of name + n + ".png".
	 * <p>
	 * Subsequent images are loaded when they are needed. See
	 * <code>next</code> and <code>previous</code> for details.
	 * @param name the name or prefix of the resource image names
	 * @exception IOException is thrown if the image or the first
	 * of the sequence cannot be found.
	 * @exception OutOfMemoryError if no memory can be allocated for
	 * the image.
	 */
	void loadImage(String prefix) throws IOException {
		this.prefix = prefix;
		Image image = null;
		images.setSize(0);
		index = 0;
		try {
			// Try the name supplied for the single image case.
			// If it is found then do the setup and return
			image = Image.createImage(prefix);
			size = 1;
		} catch (IOException ex) {
			// Use the prefix + "0.png" to locate the first of
			// a series of images.
			String name = prefix + "0.png";
			image = Image.createImage(name);
			size = 999999999;
		} 

		width = image.getWidth();
		height = image.getHeight();
		images.addElement(image);
	}

	/**
	 * Reset the Animation to reduce memory usage.
	 * Discard all but the first image.
	 */
	void reset() {
		if (images.size() > 0) {
			for (int i = 0; i < images.size(); i++)
				images.setElementAt(null, i);
		}
	}
}