从doInBackground()中调用AsyncTask.cancel(true)后,Android调用onPostExecute(),而不是调用onCancelled().但是
as per the documentation：
文档.
>从UI任务调用cancel(true)不会调用onPostExecute(),也不会抛出下面的logcat跟踪中看到的InterruptedException.
>甚至在doInBackground()返回之前,从任何线程调用cancel(false / true)有时会调用onCancelled().这显然违反了文档which states：
@H_404_3@Calling this method will result in@H_404_3@这是Android中的错误吗？ @H_404_3@更多观察： @H_404_3@>从任一线程调用cancel(false)按照中的规定工作onCancelled(Object)being invoked
on the UI thread afterdoInBackground(Object[])returns. Calling this
method guarantees thatonPostExecute(Object)is never invoked.
文档.
>从UI任务调用cancel(true)不会调用onPostExecute(),也不会抛出下面的logcat跟踪中看到的InterruptedException.
>甚至在doInBackground()返回之前,从任何线程调用cancel(false / true)有时会调用onCancelled().这显然违反了文档which states：
@H_404_3@Calling this method will result in onCancelled(Object) being invoked@H_404_3@代码:(在Android 2.2设备上测试过)
on the UI thread afterdoInBackground(Object[])returns.
protected Void doInBackground(Void... params) {
Log.d(TAG,"started doInBackground()");
while (!isCancelled()) {
boolean ret = cancel(true);
Log.d(TAG,"cancel() returned: " + ret);
}
Log.d(TAG,"returning from doInBackground()");
return null;
}
@H_404_3@Logcat输出
04-15 21:38:55.519: D/MyTask(27597): started doInBackground() 04-15 21:38:55.589: W/AsyncTask(27597): java.lang.InterruptedException 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1254) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:219) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask.get(FutureTask.java:82) 04-15 21:38:55.589: W/AsyncTask(27597): at android.os.AsyncTask$3.done(AsyncTask.java:196) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask$Sync.innerCancel(FutureTask.java:293) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask.cancel(FutureTask.java:75) 04-15 21:38:55.589: W/AsyncTask(27597): at android.os.AsyncTask.cancel(AsyncTask.java:325) 04-15 21:38:55.589: W/AsyncTask(27597): at com.example.test.TestActivity$MyTask.doInBackground(TestActivity.java:31) 04-15 21:38:55.589: W/AsyncTask(27597): at com.example.test.TestActivity$MyTask.doInBackground(TestActivity.java:1) 04-15 21:38:55.589: W/AsyncTask(27597): at android.os.AsyncTask$2.call(AsyncTask.java:185) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.FutureTask.run(FutureTask.java:137) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068) 04-15 21:38:55.589: W/AsyncTask(27597): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561) 04-15 21:38:55.589: W/AsyncTask(27597): at java.lang.Thread.run(Thread.java:1096) 04-15 21:38:55.589: D/MyTask(27597): cancel() returned: true 04-15 21:38:55.589: D/MyTask(27597): returning from doInBackground() 04-15 21:38:55.659: D/MyTask(27597): onPostExecute()
解决方法
>有一个例外,因为你调用cancel(true),它向运行doInBackground()的线程发送一个中断 – 但是,在这种情况下,你从doInBackground()中调用cancel(true),从而导致线程立即发送对自己的中断.
>您的代码在Android 2上运行,但您引用的是Android 4的文档.问题是在Android 2和Android 4之间,cancel()上的行为发生了变化. @H_404_3@Android 2.3.7 onPostExecute：
>您的代码在Android 2上运行,但您引用的是Android 4的文档.问题是在Android 2和Android 4之间,cancel()上的行为发生了变化. @H_404_3@Android 2.3.7 onPostExecute：
@H_404_3@Runs on the UI thread after doInBackground. The specified result is@H_404_3@Android 4.0.1 onPostExecute：
the value returned by doInBackground or null if the task was cancelled
or an exception occured.
@H_404_3@Runs on the UI thread after doInBackground. The specified result is the value returned by doInBackground. This method won’t be invoked if the task was cancelled.
