雙緩沖是為了防止動畫閃爍而實現(xiàn)的一種多線程應(yīng)用，基于SurfaceView的雙緩沖實現(xiàn)很簡單，開一條線程并在其中繪圖即可。本文介紹基于SurfaceView的雙緩沖實現(xiàn)，以及介紹類似的更高效的實現(xiàn)方法。

本文程序運(yùn)行截圖如下，左邊是開單個線程讀取并繪圖，右邊是開兩個線程，一個專門讀取圖片，一個專門繪圖：

對比一下，右邊動畫的幀速明顯比左邊的快，左右兩者都沒使用Thread.sleep()。為什么要開兩個線程一個讀一個畫，而不去開兩個線程像左邊那樣都 “邊讀邊畫”呢?因為SurfaceView每次繪圖都會鎖定Canvas,也就是說同一片區(qū)域這次沒畫完下次就不能畫，因此要提高雙緩沖的效率，就得開一條線程專門畫圖，開另外一條線程做預(yù)處理的工作。

[圖片] 程序運(yùn)行截圖

2. [代碼]main.xml

01

02

03 android:layout_width="fill_parent" android:layout_height="fill_parent"

04 android:orientation="vertical">

05

06

07 android:layout_width="wrap_content" android:layout_height="wrap_content">

08

09 android:layout_height="wrap_content" android:text="單個獨(dú)立線程">

10

11 android:layout_height="wrap_content" android:text="兩個獨(dú)立線程">

12

13

14 android:layout_width="fill_parent" android:layout_height="fill_parent">

15

3. [代碼]TestSurfaceView.java

001package com.testSurfaceView;

002

003import java.lang.reflect.Field;

004import java.util.ArrayList;

005import android.app.Activity;

006import android.graphics.Bitmap;

007import android.graphics.BitmapFactory;

008import android.graphics.Canvas;

009import android.graphics.Paint;

010import android.graphics.Rect;

011import android.os.Bundle;

012import android.util.Log;

013import android.view.SurfaceHolder;

014import android.view.SurfaceView;

015import android.view.View;

016import android.widget.Button;

017

018public class TestSurfaceView extends Activity {

019 /** Called when the activity is first created. */

020 Button btnSingleThread, btnDoubleThread;

021 SurfaceView sfv;

022 SurfaceHolder sfh;

023 ArrayList imgList = new ArrayList();

024 int imgWidth, imgHeight;

025 Bitmap bitmap;//獨(dú)立線程讀取，獨(dú)立線程繪圖

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());// 自動運(yùn)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();//開一條線程讀取并繪圖

048 } else if (v == btnDoubleThread) {

049 new LoadImage().start();//開一條線程讀取

050 new DrawImage(imgWidth + 10, 0).start();//開一條線程繪圖

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 // 用反射機(jī)制來獲取資源中的圖片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之外的圖片

074 {

[!--empirenews.page--]

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 // 保存圖片ID

086 imgList.add(index);

087 }

088 }

089 // 取得圖像大小

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 * 讀取并顯示圖片的線程

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);// 更新屏幕顯示內(nèi)容

128 }

129 }

130 };

131

132 /**

133 * 只負(fù)責(zé)繪圖的線程

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) {//如果圖像有效

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);// 更新屏幕顯示內(nèi)容

152 }

153 }

154 }

155 };

156

157 /**

158 * 只負(fù)責(zé)讀取圖片的線程

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())//如果到盡頭則重新讀取

169 imgIndex = 0;

170 }

171 }

172 };

 

173}