這次介紹SurfaceView的雙緩沖使用。雙緩沖是為了防止動(dòng)畫(huà)閃爍而實(shí)現(xiàn)的一種多線程應(yīng)用，基于SurfaceView的雙緩沖實(shí)現(xiàn)很簡(jiǎn)單，開(kāi)一條線程并在其中繪圖即可。本文介紹基于SurfaceView的雙緩沖實(shí)現(xiàn)，以及介紹類似的更高效的實(shí)現(xiàn)方法。
本文程序運(yùn)行截圖如下，左邊是開(kāi)單個(gè)線程讀取并繪圖，右邊是開(kāi)兩個(gè)線程，一個(gè)專門讀取圖片，一個(gè)專門繪圖：
對(duì)比一下，右邊動(dòng)畫(huà)的幀速明顯比左邊的快，左右兩者都沒(méi)使用Thread.sleep()。為什么要開(kāi)兩個(gè)線程一個(gè)讀一個(gè)畫(huà)，而不去開(kāi)兩個(gè)線程像左邊那樣都“邊讀邊畫(huà)”呢？因?yàn)镾urfaceView每次繪圖都會(huì)鎖定Canvas,也就是說(shuō)同一片區(qū)域這次沒(méi)畫(huà)完下次就不能畫(huà)，因此要提高雙緩沖的效率，就得開(kāi)一條線程專門畫(huà)圖，開(kāi)另外一條線程做預(yù)處理的工作。
main.xml的源碼：
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<?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="單個(gè)獨(dú)立線程"></Button>
<Button android:id="@+id/Button02" android:layout_width="wrap_content"
android:layout_height="wrap_content" android:text="兩個(gè)獨(dú)立線程"></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="單個(gè)獨(dú)立線程"></Button>
<Button android:id="@+id/Button02" android:layout_width="wrap_content"
android:layout_height="wrap_content" android:text="兩個(gè)獨(dú)立線程"></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<Integer> imgList = new ArrayList<Integer>();
int imgWidth, imgHeight;
Bitmap bitmap;//獨(dú)立線程讀取，獨(dú)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(dòng)運(yùn)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(kāi)一條線程讀取并繪圖
} else if (v == btnDoubleThread) {
new LoadImage().start();//開(kāi)一條線程讀取
new DrawImage(imgWidth + 10, 0).start();//開(kāi)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(jī)制來(lái)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(fù)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(fù)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;
}
}
};
}
(審核編輯: 智匯小新)
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