Android提高第三篇之SurfaceView(下)

简单介绍了SurfaceView的使用，这次就介绍SurfaceView的双缓冲使用。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的源码：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="fill_parent" android:layout_height="fill_parent"android:orientation="vertical"><LinearLayout android:id="@+id/LinearLayout01"android:layout_width="wrap_content" android:layout_height="wrap_content"><Button android:id="@+id/Button01" android:layout_width="wrap_content"android:layout_height="wrap_content" android:text="单个独立线程"></Button><Button android:id="@+id/Button02" android:layout_width="wrap_content"android:layout_height="wrap_content" android:text="两个独立线程"></Button></LinearLayout><SurfaceView android:id="@+id/SurfaceView01"android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView></LinearLayout>

本文程序的源码：

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1. package?com.testSurfaceView;????
2. import?java.lang.reflect.Field;??import?java.util.ArrayList;??
3. import?android.app.Activity;??import?android.graphics.Bitmap;??
4. import?android.graphics.BitmapFactory;??import?android.graphics.Canvas;??
5. import?android.graphics.Paint;??import?android.graphics.Rect;??
6. import?android.os.Bundle;??import?android.util.Log;??
7. import?android.view.SurfaceHolder;??import?android.view.SurfaceView;??
8. import?android.view.View;??import?android.widget.Button;??
9. ??public?class?testSurfaceView?extends?Activity?{??
10. ????/**?Called?when?the?activity?is?first?created.?*/??????Button?btnSingleThread,?btnDoubleThread;??
11. ????SurfaceView?sfv;??????SurfaceHolder?sfh;??
12. ????ArrayList<Integer>?imgList?=?new?ArrayList<Integer>();??????int?imgWidth,?imgHeight;??
13. ????Bitmap?bitmap;//独立线程读取，独立线程绘图????
14. ????@Override??????public?void?onCreate(Bundle?savedInstanceState)?{??
15. ????????super.onCreate(savedInstanceState);??????????setContentView(R.layout.main);??
16. ??????????btnSingleThread?=?(Button)?this.findViewById(R.id.Button01);??
17. ????????btnDoubleThread?=?(Button)?this.findViewById(R.id.Button02);??????????btnSingleThread.setOnClickListener(new?ClickEvent());??
18. ????????btnDoubleThread.setOnClickListener(new?ClickEvent());??????????sfv?=?(SurfaceView)?this.findViewById(R.id.SurfaceView01);??
19. ????????sfh?=?sfv.getHolder();??????????sfh.addCallback(new?MyCallBack());//?自动运行surfaceCreated以及surfaceChanged??
20. ????}????
21. ????class?ClickEvent?implements?View.OnClickListener?{????
22. ????????@Override??????????public?void?onClick(View?v)?{??
23. ??????????????if?(v?==?btnSingleThread)?{??
24. ????????????????new?Load_DrawImage(0,?0).start();//开一条线程读取并绘图??????????????}?else?if?(v?==?btnDoubleThread)?{??
25. ????????????????new?LoadImage().start();//开一条线程读取??????????????????new?DrawImage(imgWidth?+?10,?0).start();//开一条线程绘图??
26. ????????????}????
27. ????????}????
28. ????}????
29. ????class?MyCallBack?implements?SurfaceHolder.Callback?{????
30. ????????@Override??????????public?void?surfaceChanged(SurfaceHolder?holder,?int?format,?int?width,??
31. ????????????????int?height)?{??????????????Log.i("Surface:",?"Change");??
32. ??????????}??
33. ??????????@Override??
34. ????????public?void?surfaceCreated(SurfaceHolder?holder)?{??????????????Log.i("Surface:",?"Create");??
35. ??????????????//?用反射机制来获取资源中的图片ID和尺寸??
36. ????????????Field[]?fields?=?R.drawable.class.getDeclaredFields();??????????????for?(Field?field?:?fields)?{??
37. ????????????????if?(!"icon".equals(field.getName()))//?除了icon之外的图片??????????????????{??
38. ????????????????????int?index?=?0;??????????????????????try?{??
39. ????????????????????????index?=?field.getInt(R.drawable.class);??????????????????????}?catch?(IllegalArgumentException?e)?{??
40. ????????????????????????//?TODO?Auto-generated?catch?block??????????????????????????e.printStackTrace();??
41. ????????????????????}?catch?(IllegalAccessException?e)?{??????????????????????????//?TODO?Auto-generated?catch?block??
42. ????????????????????????e.printStackTrace();??????????????????????}??
43. ????????????????????//?保存图片ID??????????????????????imgList.add(index);??
44. ????????????????}??????????????}??
45. ????????????//?取得图像大小??????????????Bitmap?bmImg?=?BitmapFactory.decodeResource(getResources(),??
46. ????????????????????imgList.get(0));??????????????imgWidth?=?bmImg.getWidth();??
47. ????????????imgHeight?=?bmImg.getHeight();??????????}??
48. ??????????@Override??
49. ????????public?void?surfaceDestroyed(SurfaceHolder?holder)?{??????????????Log.i("Surface:",?"Destroy");??
50. ??????????}??
51. ??????}??
52. ??????/*?
53. ?????*?读取并显示图片的线程??????*/??
54. ????class?Load_DrawImage?extends?Thread?{??????????int?x,?y;??
55. ????????int?imgIndex?=?0;????
56. ????????public?Load_DrawImage(int?x,?int?y)?{??????????????this.x?=?x;??
57. ????????????this.y?=?y;??????????}??
58. ??????????public?void?run()?{??
59. ????????????while?(true)?{??????????????????Canvas?c?=?sfh.lockCanvas(new?Rect(this.x,?this.y,?this.x??
60. ????????????????????????+?imgWidth,?this.y?+?imgHeight));??????????????????Bitmap?bmImg?=?BitmapFactory.decodeResource(getResources(),??
61. ????????????????????????imgList.get(imgIndex));??????????????????c.drawBitmap(bmImg,?this.x,?this.y,?new?Paint());??
62. ????????????????imgIndex++;??????????????????if?(imgIndex?==?imgList.size())??
63. ????????????????????imgIndex?=?0;????
64. ????????????????sfh.unlockCanvasAndPost(c);//?更新屏幕显示内容??????????????}??
65. ????????}??????};??
66. ??????/*?
67. ?????*?只负责绘图的线程??????*/??
68. ????class?DrawImage?extends?Thread?{??????????int?x,?y;??
69. ??????????public?DrawImage(int?x,?int?y)?{??
70. ????????????this.x?=?x;??????????????this.y?=?y;??
71. ????????}????
72. ????????public?void?run()?{??????????????while?(true)?{??
73. ????????????????if?(bitmap?!=?null)?{//如果图像有效??????????????????????Canvas?c?=?sfh.lockCanvas(new?Rect(this.x,?this.y,?this.x??
74. ????????????????????????????+?imgWidth,?this.y?+?imgHeight));????
75. ????????????????????c.drawBitmap(bitmap,?this.x,?this.y,?new?Paint());????
76. ????????????????????sfh.unlockCanvasAndPost(c);//?更新屏幕显示内容??????????????????}??
77. ????????????}??????????}??
78. ????};????
79. ????/*??????*?只负责读取图片的线程?
80. ?????*/??????class?LoadImage?extends?Thread?{??
81. ????????int?imgIndex?=?0;????
82. ????????public?void?run()?{??????????????while?(true)?{??
83. ????????????????bitmap?=?BitmapFactory.decodeResource(getResources(),??????????????????????????imgList.get(imgIndex));??
84. ????????????????imgIndex++;??????????????????if?(imgIndex?==?imgList.size())//如果到尽头则重新读取??
85. ????????????????????imgIndex?=?0;??????????????}??
86. ????????}??????};??
87. }?