推箱子游戏开发（一） surfaceView 实现动画效果
SurfaceView是View的子类，常用于实现游戏中的动画效果。SurfaceView最大的特点就是：从主线程中，把具体的绘图线程独立出来。这样做的好处在于：当绘图任务比较繁重时，避免主线程的阻塞，从而提高主线程的反应速度。
废话少说，言归正传，下面用几个例子说明surfaceview的使用。
(一) 基本功能：用SurfaceView显示一副背景图片。 运行后的效果很简单，就是在屏幕上显示一副图片。 
(二) 初露锋芒：用SurfaceView显示一个动态打开的门。运行后的效果，左右两扇门缓缓打开。
如果只用SurfaceView显示一副背景图片，那绝对是“大炮打蚊子”------大材小用。从主线程中拉出一个单独的线程，就是为了处理动态效果。这里具体实现的时候有两个线程：welcomeViewGoThread和welcomeViewDrawThread。welcomeViewGoThread只负责修改图片显示的坐标，welcomeViewDrawThread负责在具体的位置显示图片。这种进一步分离，使得各模块的功能更加独立和明确。
package com.pushBox;import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.os.Bundle;import android.view.SurfaceHolder;import android.view.SurfaceView;public class PushBoxActivity extends Activity {//欢迎界面WelcomeView welcomeView = null;//欢迎界面的动画线程WelcomeViewGoThread welcomeViewGoThread = null; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //显示欢迎界面 welcomeView = new WelcomeView( this ); setContentView( welcomeView ); welcomeViewGoThread = new WelcomeViewGoThread( welcomeView ); //启动动画线程 welcomeViewGoThread.start(); } //内部类，欢迎界面 class WelcomeView extends SurfaceView implements SurfaceHolder.Callback { private SurfaceHolder holder; private WelcomeViewDrawThread welcomeViewDrawThread; //背景图片，大小640 * 480 Bitmap background; //左边的木门，大小180 * 450 Bitmap leftWood; Bitmap rightWood; //图片显示的位置 int backgroundX = 0; int backgroundY = 0; int leftWoodX = 10; int leftWoodY = 15; int rightWoodX = 150; int rightWoodY = 15; public WelcomeView( Context context ) { super( context ); holder = this.getHolder(); holder.addCallback( this ); background = BitmapFactory.decodeResource( getResources(), R.drawable.background ); leftWood = BitmapFactory.decodeResource( getResources(), R.drawable.image33 ); rightWood = BitmapFactory.decodeResource( getResources(), R.drawable.image3 ); //创建一个绘图线程 welcomeViewDrawThread = new WelcomeViewDrawThread( this, holder ); } //自定义的绘图函数，具体的绘图在这里完成 public void onDraw( Canvas c ) { c.drawBitmap( background, backgroundX, backgroundY, null ); c.drawBitmap( leftWood, leftWoodX, leftWoodY, null ); c.drawBitmap( rightWood, rightWoodX, rightWoodY, null ); } @Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {// TODO Auto-generated method stub}@Overridepublic void surfaceCreated(SurfaceHolder holder) {// TODO Auto-generated method stub//启动绘图线程welcomeViewDrawThread.setFlag( true );welcomeViewDrawThread.start();}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {// TODO Auto-generated method stubwelcomeViewDrawThread.setFlag( false );} } //内部类，欢迎界面的动画线程，只修改坐标，不负责具体显示 class WelcomeViewGoThread extends Thread { private WelcomeView welcomeView; private int sleepSpan = 200; private boolean isRun; public WelcomeViewGoThread( WelcomeView welcomeView ) { this.welcomeView = welcomeView; isRun = true; } public void setFlag( boolean flag ) { isRun = flag; } @Override public void run() { // TODO Auto-generated method stub while( isRun ) { // 修改木门坐标 welcomeView.leftWoodX -= 2; welcomeView.rightWoodX += 2; if( welcomeView.leftWoodX < -90 ) { welcomeView.leftWoodX = 10; welcomeView.rightWoodX = 150; } try{ //睡眠200毫秒 Thread.sleep( sleepSpan ); } catch(Exception e){ e.printStackTrace(); } } } } //内部类，欢迎界面的绘图线程 class WelcomeViewDrawThread extends Thread { private WelcomeView welcomeView; private SurfaceHolder holder; private boolean isRun; private int sleepSpan = 200; public WelcomeViewDrawThread( WelcomeView welcomeView, SurfaceHolder holder ) { this.welcomeView = welcomeView; this.holder = holder; isRun = true; } public void setFlag( boolean flag ) { isRun = flag; }@Overridepublic void run() {// TODO Auto-generated method stubwhile( isRun ){Canvas c = null;try{c = holder.lockCanvas();synchronized( holder ){//调用绘图函数welcomeView.onDraw( c );}}finally{if( c != null ){holder.unlockCanvasAndPost( c );}}try{//睡眠200毫秒Thread.sleep( sleepSpan );}catch(Exception e){e.printStackTrace();}}} }}(三) 脱胎换骨：修改程序框架。
上述的程序框架有问题，所有代码都放在一个文件里。下面要做的就是把相关的class都独立出来。代码改起来也很简单，只要把几个内部类单独写到一个文件即可。
(四) 重出江湖：用SurfaceView实现一个完整的欢迎界面
