Android提高21篇之三：SurfaceView與多線程配合使用

       上節中簡單介紹了SurfaceView的基本使用方法，本節主要講解SurfaceView與多線程的混搭。SurfaceView與多線程混搭，是為了防止動畫閃爍而實現的一種多線程應用。android的多線程用法與JAVA的多線程用法完全一樣，本文不做多線程方面的介紹了。直接講解SurfaceView與多線程的混合使用，即開一條線程專門讀取圖片，另外一條線程專門繪圖。

       本文程序運行截圖如下，左邊是開單個線程讀取並繪圖，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()。為什麼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，也就是說同一片區域這次沒畫完下次就不能畫，因此要提高動畫播放的效率，就得開一條線程專門畫圖，開另外一條線程做預處理的工作。

1. <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"   
2.         android:layout_width="fill_parent" android:layout_height="fill_parent"  
3.         android:orientation="vertical">  
4.   
5.         <linearlayout android:id="@+id/LinearLayout01"   
6.                 android:layout_width="wrap_content" android:layout_height="wrap_content">  
7.                 <button android:id="@+id/Button01" android:layout_width="wrap_content"   
8.                         android:layout_height="wrap_content" android:text="單個獨立線程">  
9.                 <button android:id="@+id/Button02" android:layout_width="wrap_content"   
10.                         android:layout_height="wrap_content" android:text="兩個獨立線程">  
11.           
12.         <surfaceview android:id="@+id/SurfaceView01"   
13.                 android:layout_width="fill_parent" android:layout_height="fill_parent">  

       本文程序的源碼：

1. package com.testSurfaceView;  
2.   
3. import java.lang.reflect.Field;  
4. import java.util.ArrayList;  
5. import android.app.Activity;  
6. import android.graphics.Bitmap;  
7. import android.graphics.BitmapFactory;  
8. import android.graphics.Canvas;  
9. import android.graphics.Paint;  
10. import android.graphics.Rect;  
11. import android.os.Bundle;  
12. import android.util.Log;  
13. import android.view.SurfaceHolder;  
14. import android.view.SurfaceView;  
15. import android.view.View;  
16. import android.widget.Button;  
17.   
18. public class testSurfaceView extends Activity {  
19.         /** Called when the activity is first created. */  
20.         Button btnSingleThread, btnDoubleThread;  
21.         SurfaceView sfv;  
22.         SurfaceHolder sfh;  
23.         ArrayList imgList = new ArrayList();  
24.         int imgWidth, imgHeight;  
25.         Bitmap bitmap;//獨立線程讀取，獨立線程繪圖  
26.   
27.         @Override  
28.         public void onCreate(Bundle savedInstanceState) {  
29.                 super.onCreate(savedInstanceState);  
30.                 setContentView(R.layout.main);  
31.   
32.                 btnSingleThread = (Button) this.findViewById(R.id.Button01);  
33.                 btnDoubleThread = (Button) this.findViewById(R.id.Button02);  
34.                 btnSingleThread.setOnClickListener(new ClickEvent());  
35.                 btnDoubleThread.setOnClickListener(new ClickEvent());  
36.                 sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01);  
37.                 sfh = sfv.getHolder();  
38.                 sfh.addCallback(new MyCallBack());// 自動運行surfaceCreated以及surfaceChanged  
39.         }  
40.   
41.         class ClickEvent implements View.OnClickListener {  
42.   
43.                 @Override  
44.                 public void onClick(View v) {  
45.   
46.                         if (v == btnSingleThread) {  
47.                                 new Load_DrawImage(0, 0).start();//開一條線程讀取並繪圖  
48.                         } else if (v == btnDoubleThread) {  
49.                                 new LoadImage().start();//開一條線程讀取  
50.                                 new DrawImage(imgWidth + 10, 0).start();//開一條線程繪圖  
51.                         }  
52.   
53.                 }  
54.   
55.         }  
56.   
57.         class MyCallBack implements SurfaceHolder.Callback {  
58.   
59.                 @Override  
60.                 public void surfaceChanged(SurfaceHolder holder, int format, int width,  
61.                                 int height) {  
62.                         Log.i("Surface:", "Change");  
63.   
64.                 }  
65.   
66.                 @Override  
67.                 public void surfaceCreated(SurfaceHolder holder) {  
68.                         Log.i("Surface:", "Create");  
69.   
70.                         // 用反射機制來獲取資源中的圖片ID和尺寸  
71.                         Field[] fields = R.drawable.class.getDeclaredFields();  
72.                         for (Field field : fields) {  
73.                                 if (!"icon".equals(field.getName()))// 除了icon之外的圖片  
74.                                 {  
75.                                         int index = 0;  
76.                                         try {  
77.                                                 index = field.getInt(R.drawable.class);  
78.                                         } catch (IllegalArgumentException e) {  
79.                                                 // TODO Auto-generated catch block  
80.                                                 e.printStackTrace();  
81.                                         } catch (IllegalAccessException e) {  
82.                                                 // TODO Auto-generated catch block  
83.                                                 e.printStackTrace();  
84.                                         }  
85.                                         // 保存圖片ID  
86.                                         imgList.add(index);  
87.                                 }  
88.                         }  
89.                         // 取得圖像大小  
90.                         Bitmap bmImg = BitmapFactory.decodeResource(getResources(),  
91.                                         imgList.get(0));  
92.                         imgWidth = bmImg.getWidth();  
93.                         imgHeight = bmImg.getHeight();  
94.                 }  
95.   
96.                 @Override  
97.                 public void surfaceDestroyed(SurfaceHolder holder) {  
98.                         Log.i("Surface:", "Destroy");  
99.   
100.                 }  
101.   
102.         }  
103.   
104.         /* 
105.          * 讀取並顯示圖片的線程 
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);// 更新屏幕顯示內容  
128.                         }  
129.                 }  
130.         };  
131.   
132.         /* 
133.          * 只負責繪圖的線程 
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);// 更新屏幕顯示內容  
152.                                 }  
153.                         }  
154.                 }  
155.         };  
156.   
157.         /* 
158.          * 只負責讀取圖片的線程 
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. }