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Android應(yīng)用之SurfaceView的雙緩沖使用
摘要: 這次介紹SurfaceView的雙緩沖使用。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。
關(guān)鍵詞: 存儲器 Android SurfaceView 雙緩沖
Abstract:
Key words :

這次介紹SurfaceView雙緩沖使用。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。

main.xml的源碼:

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android="http://schemas.android.com/apk/res/android" />    android:layout_width="fill_parent" android:layout_height="fill_parent" 
    android:orientation="vertical"> 
 
            android:layout_width="wrap_content" android:layout_height="wrap_content"> 
        
        
     
            android:layout_width="fill_parent" android:layout_height="fill_parent"> 
 

 android:layout_width="fill_parent" android:layout_height="fill_parent"
 android:orientation="vertical">

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

 

本文程序的源碼:

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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 imgList = new ArrayList();  
    int imgWidth, imgHeight;  
    Bitmap bitmap;//獨立線程讀取,獨立線程繪圖  
 
    @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());// 自動運行surfaceCreated以及surfaceChanged  
    }  
 
    class ClickEvent implements View.OnClickListener {  
 
        @Override 
        public void onClick(View v) {  
 
            if (v == btnSingleThread) {  
                new Load_DrawImage(0, 0).start();//開一條線程讀取并繪圖  
            } else if (v == btnDoubleThread) {  
                new LoadImage().start();//開一條線程讀取  
                new DrawImage(imgWidth + 10, 0).start();//開一條線程繪圖  
            }  
 
        }  
 
    }  
 
    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");  
 
            // 用反射機制來獲取資源中的圖片ID和尺寸  
            Field[] fields = R.drawable.class.getDeclaredFields();  
            for (Field field : fields) {  
                if (!"icon".equals(field.getName()))// 除了icon之外的圖片  
                {  
                    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();  
                    }  
                    // 保存圖片ID  
                    imgList.add(index);  
                }  
            }  
            // 取得圖像大小  
            Bitmap bmImg = BitmapFactory.decodeResource(getResources(),  
                    imgList.get(0));  
            imgWidth = bmImg.getWidth();  
            imgHeight = bmImg.getHeight();  
        }  
 
        @Override 
        public void surfaceDestroyed(SurfaceHolder holder) {  
            Log.i("Surface:", "Destroy");  
 
        }  
 
    }  
 
    /* 
     * 讀取并顯示圖片的線程 
     */ 
    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);// 更新屏幕顯示內(nèi)容  
            }  
        }  
    };  
 
    /* 
     * 只負責(zé)繪圖的線程 
     */ 
    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) {//如果圖像有效  
                    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);// 更新屏幕顯示內(nèi)容  
                }  
            }  
        }  
    };  
 
    /* 
     * 只負責(zé)讀取圖片的線程 
     */ 
    class LoadImage extends Thread {  
        int imgIndex = 0;  
 
        public void run() {  
            while (true) {  
                bitmap = BitmapFactory.decodeResource(getResources(),  
                        imgList.get(imgIndex));  
                imgIndex++;  
                if (imgIndex == imgList.size())//如果到盡頭則重新讀取  
                    imgIndex = 0;  
            }  
        }  
    };  

 

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