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 >

<?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：

 

 package  com.testSurfaceView;

 import  java.lang.reflect.Field;
 import  java.util.ArrayList;
 import  android.app.Activity;
 import  android.graphics.Bitmap;
 import  android.graphics.BitmapFactory;
 import  android.graphics.Canvas;
 import  android.graphics.Paint;
 import  android.graphics.Rect;
 import  android.os.Bundle;
 import  android.util.Log;
 import  android.view.SurfaceHolder;
 import  android.view.SurfaceView;
 import  android.view.View;
 import  android.widget.Button;

 public   class  testSurfaceView  extends  Activity {
     /** Called when the activity is first created. */
     Button btnSingleThread, btnDoubleThread;
     SurfaceView sfv;
     SurfaceHolder sfh;
     ArrayList<Integer> imgList = new  ArrayList<Integer>();
     int  imgWidth, imgHeight;
     Bitmap bitmap;//独立线程读取，独立线程绘图

     @Override
     public   void  onCreate(Bundle savedInstanceState) {
         super .onCreate(savedInstanceState);
         setContentView(R.layout.main);

         btnSingleThread = (Button) this .findViewById(R.id.Button01);
         btnDoubleThread = (Button) this .findViewById(R.id.Button02);
         btnSingleThread.setOnClickListener(new  ClickEvent());
         btnDoubleThread.setOnClickListener(new  ClickEvent());
         sfv = (SurfaceView) this .findViewById(R.id.SurfaceView01);
         sfh = sfv.getHolder();
         sfh.addCallback(new  MyCallBack()); // 自动运行surfaceCreated以及surfaceChanged
     }

     class  ClickEvent  implements  View.OnClickListener {

         @Override
         public   void  onClick(View v) {

             if  (v == btnSingleThread) {
                 new  Load_DrawImage( 0 ,  0 ).start(); //开一条线程读取并绘图
             } else   if  (v == btnDoubleThread) {
                 new  LoadImage().start(); //开一条线程读取
                 new  DrawImage(imgWidth +  10 ,  0 ).start(); //开一条线程绘图
             }

         }

     }

     class  MyCallBack  implements  SurfaceHolder.Callback {

         @Override
         public   void  surfaceChanged(SurfaceHolder holder,  int  format,  int  width,
                 int  height) {
             Log.i("Surface:" ,  "Change" );

         }

         @Override
         public   void  surfaceCreated(SurfaceHolder holder) {
             Log.i("Surface:" ,  "Create" );

             // 用反射机制来获取资源中的图片ID和尺寸
             Field[] fields = R.drawable.class .getDeclaredFields();
             for  (Field field : fields) {
                 if  (! "icon" .equals(field.getName())) // 除了icon之外的图片
                 {
                     int  index =  0 ;
                     try  {
                         index = field.getInt(R.drawable.class );
                     } catch  (IllegalArgumentException e) {
                         // TODO Auto-generated catch block
                         e.printStackTrace();
                     } catch  (IllegalAccessException e) {
                         // TODO Auto-generated catch block
                         e.printStackTrace();
                     }
                     // 保存图片ID
                     imgList.add(index);
                 }
             }
             // 取得图像大小
             Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
                     imgList.get(0 ));
             imgWidth = bmImg.getWidth();
             imgHeight = bmImg.getHeight();
         }

         @Override
         public   void  surfaceDestroyed(SurfaceHolder holder) {
             Log.i("Surface:" ,  "Destroy" );

         }

     }

     /*
      * 读取并显示图片的线程
      */
     class  Load_DrawImage  extends  Thread {
         int  x, y;
         int  imgIndex =  0 ;

         public  Load_DrawImage( int  x,  int  y) {
             this .x = x;
             this .y = y;
         }

         public   void  run() {
             while  ( true ) {
                 Canvas c = sfh.lockCanvas(new  Rect( this .x,  this .y,  this .x
                         + imgWidth, this .y + imgHeight));
                 Bitmap bmImg = BitmapFactory.decodeResource(getResources(),
                         imgList.get(imgIndex));
                 c.drawBitmap(bmImg, this .x,  this .y,  new  Paint());
                 imgIndex++;
                 if  (imgIndex == imgList.size())
                     imgIndex = 0 ;

                 sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
             }
         }
     };

     /*
      * 只负责绘图的线程
      */
     class  DrawImage  extends  Thread {
         int  x, y;

         public  DrawImage( int  x,  int  y) {
             this .x = x;
             this .y = y;
         }

         public   void  run() {
             while  ( true ) {
                 if  (bitmap !=  null ) { //如果图像有效
                     Canvas c = sfh.lockCanvas(new  Rect( this .x,  this .y,  this .x
                             + imgWidth, this .y + imgHeight));

                     c.drawBitmap(bitmap, this .x,  this .y,  new  Paint());

                     sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容
                 }
             }
         }
     };

     /*
      * 只负责读取图片的线程
      */
     class  LoadImage  extends  Thread {
         int  imgIndex =  0 ;

         public   void  run() {
             while  ( true ) {
                 bitmap = BitmapFactory.decodeResource(getResources(),
                         imgList.get(imgIndex));
                 imgIndex++;
                 if  (imgIndex == imgList.size()) //如果到尽头则重新读取
                     imgIndex = 0 ;
             }
         }
     };
 }