本人进行过模拟測试，发现AsyncTask并不适合多任务，以及长期的异步任务，由于每次仅仅能执行一个AsyncTask，假设执行多个其他任务将会等待
以下通过一个代码样例和日志打印得到证实。
以下扩展了2个AsyncTask，分别调用了2次，一共调用了四次。
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 4个异步一起运行,2个不同的实现对象
new MyTask().execute("http://www.baidu.com/img/bdlogo.png");
new MyTask2().execute("http://www.baidu.com/img/bdlogo.png");
new MyTask2().execute("http://www.baidu.com/img/bdlogo.png");
new MyTask().execute("http://www.baidu.com/img/bdlogo.png");
}
public class MyTask2 extends AsyncTask<String, Integer, Bitmap> {
public MyTask2() {
super();
}
@Override
protected void onPostExecute(Bitmap result) {
Log.d("MainActivity", "onPostExecute");
updateImageView(result);
}
@Override
protected void onPreExecute() {
Log.d("MainActivity", "onPreExecute");
}
@Override
protected Bitmap doInBackground(String... args) {
Log.e("MainActivity", "MyTask2：" + THREAD_POOL_EXECUTOR); // static对象都一样，运行的线程池
Log.e("MainActivity", "MyTask2：" + SERIAL_EXECUTOR); // static对象都一样，运行任务的
String website = args[0];
HttpURLConnection conn = null;
InputStream ins = null;
try {
for (int i = 0; i < 10; i++) {
Thread.sleep((int) (Math.random() * 100 + 800)); <span style="font-family: Arial, Helvetica, sans-serif;">//有益休眠</span>
Log.d("MainActivity", "MyTask2:" + i + " " + Thread.currentThread().getName() + " id:"
+ Thread.currentThread().getId());
}
URL url = new URL(website);
conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5000);
conn.setDoInput(true);
if (conn.getResponseCode() == 200) {
Log.d("MainActivity", "MyTask2:" + "get image is ok");
ins = conn.getInputStream();
return BitmapFactory.decodeStream(ins);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (ins != null) {
try {
ins.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return null;
}
}
public class MyTask extends AsyncTask<String, Integer, Bitmap> {
public MyTask() {
super();
}
@Override
protected void onPostExecute(Bitmap result) {
Log.d("MainActivity", "onPostExecute");
updateImageView(result);
}
@Override
protected void onPreExecute() {
Log.d("MainActivity", "onPreExecute");
}
@Override
protected Bitmap doInBackground(String... args) {
Log.e("MainActivity", "MyTask：" + THREAD_POOL_EXECUTOR);
Log.e("MainActivity", "MyTask：" + SERIAL_EXECUTOR);
for (int i = 0; i < 10; i++) {
try {
Thread.sleep((int) (Math.random() * 100 + 600));//有益休眠
} catch (InterruptedException e) {
e.printStackTrace();
}
Log.d("MainActivity", "MyTask:" + i + " " + Thread.currentThread().getName() + " id:"
+ Thread.currentThread().getId());
}
String website = args[0];
HttpURLConnection conn = null;
InputStream ins = null;
try {
URL url = new URL(website);
conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5000);
conn.setDoInput(true);
if (conn.getResponseCode() == 200) {
Log.d("MainActivity", "get image is ok");
ins = conn.getInputStream();
return BitmapFactory.decodeStream(ins);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ins != null) {
try {
ins.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return null;
}
}
boolean f = false;
public void updateImageView(Bitmap result) {
if (result != null) {
ImageView img = (ImageView) findViewById(R.id.img);
img.setImageBitmap(result);
}
}
}4个异步执行发现，第一个必须执行完才干执行下一个？ 仅仅是我理解不正确，还是使用方法有问题，假设有朋友知道请指正。
打印日志例如以下：
12-17 05:24:57.665: D/MainActivity(25755): onPreExecute
12-17 05:24:57.665: D/dalvikvm(25755): create interp thread : stack size=32KB
12-17 05:24:57.665: D/dalvikvm(25755): create new thread
12-17 05:24:57.666: D/dalvikvm(25755): new thread created
12-17 05:24:57.666: D/dalvikvm(25755): update thread list
12-17 05:24:57.666: D/dalvikvm(25755): threadid=16: interp stack at 0x5e677000
12-17 05:24:57.666: D/dalvikvm(25755): threadid=16: created from interp
12-17 05:24:57.666: D/dalvikvm(25755): start new thread
12-17 05:24:57.666: D/dalvikvm(25755): threadid=16: notify debugger
12-17 05:24:57.666: D/dalvikvm(25755): threadid=16 (AsyncTask #5): calling run()
12-17 05:24:57.666: D/MainActivity(25755): onPreExecute
<span style="color:#ff0000;">12-17 05:24:57.666: E/MainActivity(25755): MyTask：java.util.concurrent.ThreadPoolExecutor@42258eb8[Running, pool size = 5, active threads = 1, queued tasks = 0, completed tasks = 4]
12-17 05:24:57.666: E/MainActivity(25755): MyTask：android.os.AsyncTask$SerialExecutor@42258fc8</span>
12-17 05:24:57.669: D/MainActivity(25755): onPreExecute
12-17 05:24:57.669: D/MainActivity(25755): onPreExecute
12-17 05:24:57.731: V/InputMethodManager(25755): onWindowFocus: null softInputMode=288 first=true flags=#1810100
12-17 05:24:57.731: V/InputMethodManager(25755): START INPUT: com.android.internal.policy.impl.PhoneWindow$DecorView{422f7c58 V.E..... R.....ID 0,0-1080,1920} ic=null tba=android.view.inputmethod.EditorInfo@422fe938 controlFlags=#104
12-17 05:24:57.733: V/InputMethodManager(25755): Starting input: Bind result=InputBindResult{com.android.internal.view.IInputMethodSession$Stub$Proxy@42301bb0 com.android.inputmethod.latin/.LatinIME #609}
12-17 05:24:58.281: D/MainActivity(25755): MyTask:0 AsyncTask #5 id:4784
12-17 05:24:58.966: D/MainActivity(25755): MyTask:1 AsyncTask #5 id:4784
12-17 05:24:59.643: D/MainActivity(25755): MyTask:2 AsyncTask #5 id:4784
12-17 05:25:00.276: D/MainActivity(25755): MyTask:3 AsyncTask #5 id:4784
12-17 05:25:00.946: D/MainActivity(25755): MyTask:4 AsyncTask #5 id:4784
12-17 05:25:01.589: D/MainActivity(25755): MyTask:5 AsyncTask #5 id:4784
12-17 05:25:02.224: D/MainActivity(25755): MyTask:6 AsyncTask #5 id:4784
12-17 05:25:02.842: D/MainActivity(25755): MyTask:7 AsyncTask #5 id:4784
12-17 05:25:03.464: D/MainActivity(25755): MyTask:8 AsyncTask #5 id:4784
12-17 05:25:04.120: D/MainActivity(25755): MyTask:9 AsyncTask #5 id:4784
12-17 05:25:04.123: I/System.out(25755): [CDS]rx timeout:0
12-17 05:25:04.125: I/System.out(25755): [CDS]close[48692]
12-17 05:25:04.126: I/System.out(25755): close [socket][/0.0.0.0:48692]
12-17 05:25:04.430: D/libc-netbsd(25755): getaddrinfo: www.baidu.com get result from proxy >>
12-17 05:25:04.430: I/System.out(25755): propertyValue:true
12-17 05:25:04.431: I/System.out(25755): [socket][1] connection www.baidu.com/180.97.33.107:80;LocalPort=38503(5000)
12-17 05:25:04.431: I/System.out(25755): [CDS]connect[www.baidu.com/180.97.33.107:80] tm:5
12-17 05:25:04.432: D/Posix(25755): [Posix_connect Debug]Process com.example.asynctaskdemo :80
12-17 05:25:04.547: I/System.out(25755): [socket][/192.168.2.122:38503] connected
12-17 05:25:04.547: I/System.out(25755): [CDS]rx timeout:0
12-17 05:25:04.613: D/MainActivity(25755): get image is ok
12-17 05:25:04.643: D/dalvikvm(25755): GC_FOR_ALLOC freed 677K (925), 32% free 3736K/5484K, paused 23ms, total 28ms
12-17 05:25:04.646: D/skia(25755): Flag is not 10
12-17 05:25:04.647: D/MainActivity(25755): onPostExecute
<span style="color:#ff0000;">12-17 05:25:04.648: E/MainActivity(25755): MyTask2：java.util.concurrent.ThreadPoolExecutor@42258eb8[Running, pool size = 5, active threads = 1, queued tasks = 0, completed tasks = 5]
12-17 05:25:04.648: E/MainActivity(25755): MyTask2：android.os.AsyncTask$SerialExecutor@42258fc8</span>
12-17 05:25:04.668: I/SurfaceTextureClient(25755): [STC::queueBuffer] (this:0x5eee0028) fps:0.14, dur:6910.24, max:6910.24, min:6910.24
12-17 05:25:04.668: I/SurfaceTextureClient(25755): [STC::queueBuffer] this:0x5eee0028, api:1, last queue time elapsed:6910.24
12-17 05:25:05.485: D/MainActivity(25755): MyTask2:0 AsyncTask #5 id:4784
12-17 05:25:06.323: D/MainActivity(25755): MyTask2:1 AsyncTask #5 id:4784
12-17 05:25:07.217: D/MainActivity(25755): MyTask2:2 AsyncTask #5 id:4784
12-17 05:25:08.107: D/MainActivity(25755): MyTask2:3 AsyncTask #5 id:4784
12-17 05:25:09.002: D/MainActivity(25755): MyTask2:4 AsyncTask #5 id:4784
12-17 05:25:09.881: D/MainActivity(25755): MyTask2:5 AsyncTask #5 id:4784
12-17 05:25:10.771: D/MainActivity(25755): MyTask2:6 AsyncTask #5 id:4784
12-17 05:25:11.579: D/MainActivity(25755): MyTask2:7 AsyncTask #5 id:4784
12-17 05:25:12.445: D/MainActivity(25755): MyTask2:8 AsyncTask #5 id:4784
12-17 05:25:13.299: D/MainActivity(25755): MyTask2:9 AsyncTask #5 id:4784
12-17 05:25:13.300: I/System.out(25755): [CDS]rx timeout:0
12-17 05:25:13.586: D/MainActivity(25755): MyTask2:get image is ok
12-17 05:25:13.610: D/dalvikvm(25755): GC_FOR_ALLOC freed 688K (1136), 33% free 3689K/5484K, paused 21ms, total 21ms
12-17 05:25:13.613: D/skia(25755): Flag is not 10
12-17 05:25:13.613: D/MainActivity(25755): onPostExecute
<span style="color:#ff6666;">12-17 05:25:13.615: E/MainActivity(25755): MyTask2：java.util.concurrent.ThreadPoolExecutor@42258eb8[Running, pool size = 5, active threads = 1, queued tasks = 0, completed tasks = 6]
12-17 05:25:13.615: E/MainActivity(25755): MyTask2：android.os.AsyncTask$SerialExecutor@42258fc8</span>
12-17 05:25:13.630: I/SurfaceTextureClient(25755): [STC::queueBuffer] (this:0x5eee0028) fps:0.11, dur:8961.83, max:8961.83, min:8961.83
12-17 05:25:13.630: I/SurfaceTextureClient(25755): [STC::queueBuffer] this:0x5eee0028, api:1, last queue time elapsed:8961.83
12-17 05:25:14.455: D/MainActivity(25755): MyTask2:0 AsyncTask #5 id:4784
12-17 05:25:15.304: D/MainActivity(25755): MyTask2:1 AsyncTask #5 id:4784
12-17 05:25:16.104: D/MainActivity(25755): MyTask2:2 AsyncTask #5 id:4784
12-17 05:25:17.008: D/MainActivity(25755): MyTask2:3 AsyncTask #5 id:4784
12-17 05:25:17.887: D/MainActivity(25755): MyTask2:4 AsyncTask #5 id:4784
12-17 05:25:18.737: D/MainActivity(25755): MyTask2:5 AsyncTask #5 id:4784
12-17 05:25:19.584: D/MainActivity(25755): MyTask2:6 AsyncTask #5 id:4784
12-17 05:25:20.399: D/MainActivity(25755): MyTask2:7 AsyncTask #5 id:4784
12-17 05:25:21.281: D/MainActivity(25755): MyTask2:8 AsyncTask #5 id:4784
12-17 05:25:22.130: D/MainActivity(25755): MyTask2:9 AsyncTask #5 id:4784
12-17 05:25:22.132: I/System.out(25755): [CDS]rx timeout:0
12-17 05:25:22.178: D/MainActivity(25755): MyTask2:get image is ok
12-17 05:25:22.202: D/dalvikvm(25755): GC_FOR_ALLOC freed 641K (300), 33% free 3689K/5484K, paused 21ms, total 22ms
12-17 05:25:22.208: D/skia(25755): Flag is not 10
12-17 05:25:22.209: D/MainActivity(25755): onPostExecute
<span style="color:#ff0000;">12-17 05:25:22.211: E/MainActivity(25755): MyTask：java.util.concurrent.ThreadPoolExecutor@42258eb8[Running, pool size = 5, active threads = 1, queued tasks = 0, completed tasks = 7]
12-17 05:25:22.211: E/MainActivity(25755): MyTask：android.os.AsyncTask$SerialExecutor@42258fc8</span>
12-17 05:25:22.219: I/SurfaceTextureClient(25755): [STC::queueBuffer] (this:0x5eee0028) fps:0.12, dur:8589.36, max:8589.36, min:8589.36
12-17 05:25:22.219: I/SurfaceTextureClient(25755): [STC::queueBuffer] this:0x5eee0028, api:1, last queue time elapsed:8589.36
12-17 05:25:22.839: D/MainActivity(25755): MyTask:0 AsyncTask #5 id:4784
12-17 05:25:23.519: D/MainActivity(25755): MyTask:1 AsyncTask #5 id:4784
12-17 05:25:24.176: D/MainActivity(25755): MyTask:2 AsyncTask #5 id:4784
12-17 05:25:24.786: D/MainActivity(25755): MyTask:3 AsyncTask #5 id:4784
12-17 05:25:25.440: D/MainActivity(25755): MyTask:4 AsyncTask #5 id:4784
12-17 05:25:26.134: D/MainActivity(25755): MyTask:5 AsyncTask #5 id:4784
12-17 05:25:26.740: D/MainActivity(25755): MyTask:6 AsyncTask #5 id:4784
12-17 05:25:27.367: D/MainActivity(25755): MyTask:7 AsyncTask #5 id:4784
12-17 05:25:27.988: D/MainActivity(25755): MyTask:8 AsyncTask #5 id:4784
12-17 05:25:28.617: D/MainActivity(25755): MyTask:9 AsyncTask #5 id:4784
12-17 05:25:28.618: I/System.out(25755): [CDS]rx timeout:0
12-17 05:25:28.658: D/MainActivity(25755): get image is ok
12-17 05:25:28.681: D/dalvikvm(25755): GC_FOR_ALLOC freed 641K (299), 33% free 3689K/5484K, paused 20ms, total 21ms
12-17 05:25:28.683: D/skia(25755): Flag is not 10
12-17 05:25:28.684: D/MainActivity(25755): onPostExecute
12-17 05:25:28.694: I/SurfaceTextureClient(25755): [STC::queueBuffer] (this:0x5eee0028) fps:0.15, dur:6474.71, max:6474.71, min:6474.71
12-17 05:25:28.694: I/SurfaceTextureClient(25755): [STC::queueBuffer] this:0x5eee0028, api:1, last queue time elapsed:6474.71发现ThreadPool每次仅仅有1个线程在执行，一个时刻仅仅能执行一次。上面执行的情况是线程被反复利用了，
手机上执行线程NAME和ID都是一样，在模拟器上执行ID和NAME即便是不一样 也是顺序执行的，并没有同一时候执行多个任务的情况发现。
个人经过測试发现，AsyncTask 仅仅能用一次，假设实例化多个AsyncTask 并不能提高执行效率，不能利用多任务的情况。不知道是不是这样，google设计这个AsyncTask的目的仅仅是用来执行一次异步任务，和UI更新？ 如有朋友知道详细理由请指出,，谢谢。