blocks|key|2031545|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2031546|是否可以创建另一个异步任务并从第一个异步任务开始执行？|blockquote|2031547|2031548|2031549|是的，但只能在onProgressUpdate()或onPostExecute()内部，因为这些方法在UI线程上运行。因此，通过选择上面列出的两种方法之一，在UI线程上启动第二个AsyncTask。|offset|length|style|CODE|2031550|我想知道第二个任务中的publishProgress()会做什么……因为它不是从活动开始的？|2031551|2031552|它做的是完全相同的事情，因为您是从UI线程启动它的。|2031553|entityMap^0|0|0|0|0|7|I|Q|F|2H|9|0|0|0|0^^$0|@$1|2|3|-4|4|5|6|S|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|T|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|U|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|V|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|W|7|@$H|X|I|Y|J|K]|$H|Z|I|10|J|K]|$H|11|I|12|J|K]]|8|@]|9|$]]|$1|L|3|M|4|5|6|13|7|@]|8|@]|9|$]]|$1|N|3|-4|4|5|6|14|7|@]|8|@]|9|$]]|$1|O|3|P|4|5|6|15|7|@]|8|@]|9|$]]|$1|Q|3|-4|4|5|6|16|7|@]|8|@]|9|$]]]|R|$]]

<blockquote>
 Is it acceptable to create another
 asynctask &amp; execute it from the first
 one?
</blockquote>

Yes, but only inside <code>onProgressUpdate()</code> or <code>onPostExecute()</code> since these methods runs on the UI thread. Therefore, start the second <code>AsyncTask</code> on the UI thread by choosing one of the two methods listed above.

<blockquote>
 I'm wondering what publishProgress()
 from the second task would even do...
 since it was not started from an
 Activity?
</blockquote>

It does exactly the same thing, since you are starting it from the UI thread.

blocks|key|2373153|text|如果你正在寻找一种执行多个异步任务的机制，从3.0开始，它支持一种名为executeOnExecutor的方法，该方法允许你在异步任务管理的线程池中并行调度任务。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2373154|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.android.com/reference/android/os/AsyncTask.html#executeOnExecutor%2528java.util.concurrent.Executor,%2520Params...%2529^0|Z|H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

If you are looking for a mechanism of executing multiple async tasks, from 3.0 and above it supports a method called <a href="http://developer.android.com/reference/android/os/AsyncTask.html#executeOnExecutor%28java.util.concurrent.Executor,%20Params...%29" rel="noreferrer">executeOnExecutor</a> which will allow you to schedule tasks in parallel on a pool of thread managed by Async Task.

blocks|key|411720|text|在与主线程通信以处理UI更改时，AsyncTask对于执行一些后台工作很有用。看起来这不是你的情况。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|411721|此外，必须从主线程执行AsyncTask。从AsyncTask参考中：|411722|411723|要使该类正常工作，必须遵循以下几条线程规则：|blockquote|411724|411725|411726|必须在UI+thread.|411727|execute(Params...)上创建|unordered-list-item|411728|任务实例必须在UI线程上调用。|411729|411730|411731|你可以看看这个article，看看什么最适合你。|offset|length|411732|entityMap|0|LINK|mutability|MUTABLE|url|http://techtej.blogspot.com/2011/03/android-thread-constructspart-4.html^0|0|0|0|0|0|0|0|0|0|0|0|7|7|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|17|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|19|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1A|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|N|7|1C|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1F|8|@]|9|@$U|1G|V|1H|1|1I]]|A|$]]|$1|W|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|X|$Y|$5|Z|10|11|A|$12|13]]]]

An AsyncTask is useful for doing some background work while communicating with the main thread to handle UI changes. It appears that this is not your case.

Besides, an AsyncTask must be executed from the main thread. From the AsyncTask reference:

<blockquote>
 There are a few threading rules that
 must be followed for this class to
 work properly:
 
 <ul>
 <li>The task instance must be created on the UI thread.</li>
 <li>execute(Params...) must be invoked on the UI thread.</li>
 </ul>
</blockquote>

You can a take a look at this <a href="http://techtej.blogspot.com/2011/03/android-thread-constructspart-4.html" rel="nofollow">article</a> and see what fits you best.

blocks|key|2031603|text|这可以使用消息传递并发和单个处理程序来完成。概念证明代码如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2031604|private+Handler+myHandler=+new+Handler(){
++++@Override
++++public+void++handleMessage(Message+msg){+++++++++
++++++++switch(msg.what){
++++++++++++case+0:
++++++++++++++++Toast.makeText(Main.this,"Message0",+Toast.LENGTH_SHORT).show();
++++++++++++++++Thread+thread=+new+Thread(+new+Runnable()+{
++++++++++++++++++++public+void+run()+{
++++++++++++++++++++++++try+{
++++++++++++++++++++++++++++Thread.sleep(3000);
++++++++++++++++++++++++}
++++++++++++++++++++++++catch(Exception+e){}
++++++++++++++++++++++++myHandler.sendEmptyMessage(2);
++++++++++++++++++++}+++++++
++++++++++++++++});
++++++++++++++++thread.setDaemon(true);+//+<==+I+am+a+service+provider.+KILL+ME+if+the+non-daemon+thread+ConfuseText+quits
++++++++++++++++thread.start();+++

++++++++++++break;
++++++++++++case+1:
++++++++++++++++Toast.makeText(Main.this,"Message1",+Toast.LENGTH_SHORT).show();
++++++++++++++++break;
++++++++++++case+2:
++++++++++++++++Toast.makeText(Main.this,"Message2",+Toast.LENGTH_SHORT).show();
++++++++++++++++break;
++++++++++++default:
++++++++++++++++super.handleMessage(msg);
++++++++++++++++break;
++++++++}
++++}
};|code-block|syntax|javascript|2031605|我在单击按钮时启动了第一个线程，如下所示：|2031606|+ON+CLICK+HANDLER
++++++++++++threadButton.setOnClickListener(new+View.OnClickListener()+{
++++++++++++@Override
++++++++++++public+void+onClick(View+arg0)+{
++++++++++++++++//+TODO+Auto-generated+method+stub
++++++++++++++++Thread+thread=+new+Thread(+new+Runnable()+{
++++++++++++++++++++public+void+run()+{
++++++++++++++++++++++++try+{
++++++++++++++++++++++++Thread.sleep(1000);
++++++++++++++++++++++++}
++++++++++++++++++++++++catch(Exception+e){+
++++++++++++++++++++++++}
++++++++++++++++++++++++myHandler.sendEmptyMessage(0);
++++++++++++++++++++++++try+{
++++++++++++++++++++++++Thread.sleep(3000);
++++++++++++++++++++++++}
++++++++++++++++++++++++catch(Exception+e){+
++++++++++++++++++++++++}
++++++++++++++++++++++++myHandler.sendEmptyMessage(1);
++++++++++++++++++++}
++++++++++++++++});
++++++++++++++++thread.setDaemon(true);+//+<==+I+am+a+service+provider.+KILL+ME+if+the+non-daemon+thread+ConfuseText+quits
++++++++++++++++thread.start();
++++++++++++}
});|2031607|对线程睡眠的调用是为了模拟时间密集型任务。|2031608|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

This can be done using message passing concurrency and a single handler. Proof of concept code follows: 

<pre><code>private Handler myHandler= new Handler(){
 @Override
 public void handleMessage(Message msg){ 
 switch(msg.what){
 case 0:
 Toast.makeText(Main.this,"Message0", Toast.LENGTH_SHORT).show();
 Thread thread= new Thread( new Runnable() {
 public void run() {
 try {
 Thread.sleep(3000);
 }
 catch(Exception e){}
 myHandler.sendEmptyMessage(2);
 } 
 });
 thread.setDaemon(true); // &lt;== I am a service provider. KILL ME if the non-daemon thread ConfuseText quits
 thread.start(); 

 break;
 case 1:
 Toast.makeText(Main.this,"Message1", Toast.LENGTH_SHORT).show();
 break;
 case 2:
 Toast.makeText(Main.this,"Message2", Toast.LENGTH_SHORT).show();
 break;
 default:
 super.handleMessage(msg);
 break;
 }
 }
};
</code></pre>

I launched the first thread on a button click as in:

<pre><code> ON CLICK HANDLER
 threadButton.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View arg0) {
 // TODO Auto-generated method stub
 Thread thread= new Thread( new Runnable() {
 public void run() {
 try {
 Thread.sleep(1000);
 }
 catch(Exception e){ 
 }
 myHandler.sendEmptyMessage(0);
 try {
 Thread.sleep(3000);
 }
 catch(Exception e){ 
 }
 myHandler.sendEmptyMessage(1);
 }
 });
 thread.setDaemon(true); // &lt;== I am a service provider. KILL ME if the non-daemon thread ConfuseText quits
 thread.start();
 }
});
</code></pre>

The calls to thread sleep is to mimic a time intensive task.

At a certain point of my AsyncTask, after some validations have been done, I need to spawn off another thread to do some other work. So I'd like two background threads at this point, each doing it's own thing (approx 2-3 seconds to execute each). The idea is to maximize performance on dual core processors like Atrix.

Is it acceptable to create another asynctask &amp; execute it from the first one? Can anyone suggest a better way of doing this?

Thanks!

EDIT: I'm wondering what publishProgress() from the second task would even do... since it was not started from an Activity?

Calling an AsyncTask from another AsyncTask

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在我的AsyncTask的某个点上，在完成一些验证之后，我需要产生另一个线程来做一些其他工作。因此，我希望在这一点上有两个后台线程，每个线程都做自己的事情(大约2-3秒来执行)。这个想法是为了最大化像Atrix这样的双核处理器的性能。是否可以创建另一个异步任务并从第一个异步任务开始执行？有没有人能推荐一种更好的方法呢？谢谢!编辑:我想知道第二个任务的publishProgress()会做什么……因

问从另一个AsyncTask调用AsyncTask
EN

回答 4

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