双缓冲是为了防止动画闪烁而实现的一种多线程应用，基于SurfaceView的双缓冲实现很简单，开一条线程并在其中绘图即可。本文介绍基于SurfaceView的双缓冲实现，以及介绍类似的更高效的实现方法。
本文程序运行截图如下，左边是开单个线程读取并绘图，右边是开两个线程，一个专门读取图片，一个专门绘图：
对比一下，右边动画的帧速明显比左边的快，左右两者都没使用Thread.sleep()。为什么要开两个线程一个读一个画，而不去开两个线程像左边那样都 “边读边画”呢？因为SurfaceView每次绘图都会锁定Canvas,也就是说同一片区域这次没画完下次就不能画，因此要提高双缓冲的效率，就得开一条线程专门画图，开另外一条线程做预处理的工作。
main.xml
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01 <?xml version="1.0" encoding="utf-8"?>
02 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
03 android:layout_width="fill_parent" android:layout_height="fill_parent"
04 android:orientation="vertical">
05
06 <LinearLayout android:id="@+id/LinearLayout01"
07 android:layout_width="wrap_content" android:layout_height="wrap_content">
08 <Button android:id="@+id/Button01" android:layout_width="wrap_content"
09 android:layout_height="wrap_content" android:text="单个独立线程"></Button>
10 <Button android:id="@+id/Button02" android:layout_width="wrap_content"
11 android:layout_height="wrap_content" android:text="两个独立线程"></Button>
12 </LinearLayout>
13 <SurfaceView android:id="@+id/SurfaceView01"
14 android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView>
15 </LinearLayout>
[代码] TestSurfaceView.java
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001 package com.testSurfaceView;
002
003 import java.lang.reflect.Field;
004 import java.util.ArrayList;
005 import android.app.Activity;
006 import android.graphics.Bitmap;
007 import android.graphics.BitmapFactory;
008 import android.graphics.Canvas;
009 import android.graphics.Paint;
010 import android.graphics.Rect;
011 import android.os.Bundle;
012 import android.util.Log;
013 import android.view.SurfaceHolder;
014 import android.view.SurfaceView;
015 import android.view.View;
016 import android.widget.Button;
017
018 public class TestSurfaceView extends Activity {
019 /** Called when the activity is first created. */
020 Button btnSingleThread, btnDoubleThread;
021 SurfaceView sfv;
022 SurfaceHolder sfh;
023 ArrayList<Integer> imgList = new ArrayList<Integer>();
024 int imgWidth, imgHeight;
025 Bitmap bitmap;//独立线程读取，独立线程绘图
026
027 @Override
028 public void onCreate(Bundle savedInstanceState) {
029 super.onCreate(savedInstanceState);
030 setContentView(R.layout.main);
031
032 btnSingleThread = (Button) this.findViewById(R.id.Button01);
033 btnDoubleThread = (Button) this.findViewById(R.id.Button02);
034 btnSingleThread.setOnClickListener(new ClickEvent());
035 btnDoubleThread.setOnClickListener(new ClickEvent());
036 sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01);
037 sfh = sfv.getHolder();
038 sfh.addCallback(new MyCallBack());// 自动运行surfaceCreated以及surfaceChanged
039 }
040
041 class ClickEvent implements View.OnClickListener {
042
043 @Override
044 public void onClick(View v) {
045
046 if (v == btnSingleThread) {
047 new Load_DrawImage(0, 0).start();//开一条线程读取并绘图
048 } else if (v == btnDoubleThread) {
049 new LoadImage().start();//开一条线程读取
050 new DrawImage(imgWidth + 10, 0).start();//开一条线程绘图
051 }
052
053 }
054
055 }
056
057 class MyCallBack implements SurfaceHolder.Callback {
058
059 @Override
060 public void surfaceChanged(SurfaceHolder holder, int format, int width,
061 int height) {
062 Log.i("Surface:", "Change");
063
064 }
065
066 @Override
067 public void surfaceCreated(SurfaceHolder holder) {
068 Log.i("Surface:", "Create");
069
070 // 用反射机制来获取资源中的图片ID和尺寸
071 Field[] fields = R.drawable.class.getDeclaredFields();
072 for (Field field : fields) {
073 if (!"icon".equals(field.getName()))// 除了icon之外的图片
074 {
075 int index = 0;
076 try {
077 index = field.getInt(R.drawable.class);
078 } catch (IllegalArgumentException e) {
079 // TODO Auto-generated catch block
080 e.printStackTrace();
081 } catch (IllegalAccessException e) {
082 // TODO Auto-generated catch block
083 e.printStackTrace();
084 }
085 // 保存图片ID
086 imgList.add(index);
087 }
088 }
089 // 取得图像大小
090 Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
091 imgList.get(0));
092 imgWidth = bmImg.getWidth();
093 imgHeight = bmImg.getHeight();
094 }
095
096 @Override
097 public void surfaceDestroyed(SurfaceHolder holder) {
098 Log.i("Surface:", "Destroy");
099
100 }
101
102 }
103
104 /**
105 * 读取并显示图片的线程
106 */
107 class Load_DrawImage extends Thread {
108 int x, y;
109 int imgIndex = 0;
110
111 public Load_DrawImage(int x, int y) {
112 this.x = x;
113 this.y = y;
114 }
115
116 public void run() {
117 while (true) {
118 Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x
119 + imgWidth, this.y + imgHeight));
120 Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
121 imgList.get(imgIndex));
122 c.drawBitmap(bmImg, this.x, this.y, new Paint());
123 imgIndex++;
124 if (imgIndex == imgList.size())
125 imgIndex = 0;
126
127 sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
128 }
129 }
130 };
131
132 /**
133 * 只负责绘图的线程
134 */
135 class DrawImage extends Thread {
136 int x, y;
137
138 public DrawImage(int x, int y) {
139 this.x = x;
140 this.y = y;
141 }
142
143 public void run() {
144 while (true) {
145 if (bitmap != null) {//如果图像有效
146 Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x
147 + imgWidth, this.y + imgHeight));
148
149 c.drawBitmap(bitmap, this.x, this.y, new Paint());
150
151 sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
152 }
153 }
154 }
155 };
156
157 /**
158 * 只负责读取图片的线程
159 */
160 class LoadImage extends Thread {
161 int imgIndex = 0;
162
163 public void run() {
164 while (true) {
165 bitmap = BitmapFactory.decodeResource(getResources(),
166 imgList.get(imgIndex));
167 imgIndex++;
168 if (imgIndex == imgList.size())//如果到尽头则重新读取
169 imgIndex = 0;
170 }
171 }
172 };
173 }