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的一種多線程應用，基于SurfaceView的雙緩沖實現很簡單，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，以及介紹類似的更高效的實現方法。
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處理的工作。
main.xml的源碼：
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android:orientation="vertical">
android:orientation="vertical">
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
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);// 更新屏幕顯示內容
}
}
};
/*
* 只負責繪圖的線程
*/
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);// 更新屏幕顯示內容
}
}
}
};
/*
* 只負責讀取圖片的線程
*/
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;
}
}
};
}