translatecanvas.java

Java ME手机应用开发大全一书的配套光盘上的源码

package com.j2medev.translate;

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;

class TranslateCanvas extends Canvas implements CommandListener {
    private Command cmExit;
    private Translate midlet;
    private Image im = null;
    private int translatex = 0, translatey = 0;
    public TranslateCanvas(Translate midlet) {
        this.midlet = midlet;
        cmExit = new Command("Exit", Command.EXIT, 1);
        addCommand(cmExit);
        setCommandListener(this);
        
        try {
            //创建图片
            im = Image.createImage("/img.png");
        } catch (java.io.IOException e) {
            System.err.println("Unable to locate or read .png file");
        }
    }
    
    protected void paint(Graphics g) {
        if (im != null) {
            //清屏
            g.setColor(255, 255, 255);
            g.fillRect(0, 0, getWidth(), getHeight());
            //变换坐标，请参考Graphics.translate(x,y)方法说明
            g.translate(translatex, translatey);
            //总是在原点处画图片，由于前面变换了坐标 看起来同样图片会动起来
            g.drawImage(im, 0, 0, Graphics.LEFT | Graphics.TOP);
        }
    }
    
    public void commandAction(Command c, Displayable d) {
        if (c == cmExit)
            midlet.exitMIDlet();
    }
    protected void keyPressed(int keyCode) {
        switch (getGameAction(keyCode)) {
            case UP:
                break;
            case DOWN:
                break;
            case LEFT:
                // 图片右边缘已经到达屏幕最右边
                System.out.println(translatex);
                System.out.println(im.getWidth());
                if (translatex + im.getWidth() < getWidth())
                    return;//直接返回
                else
                    translatex -= 2;
                break;
                
            case RIGHT:
                // 滚动到图片的左边缘
                if (translatex>getWidth()-2)
                    return;
                else
                    translatex += 2;
                break;
        }
        repaint();
    }
}