android - AsyncTask onCancelled() 和 AsyncTask.doInBackground() 的执行时机

Question

根据 AsyncTask.cancel method 的 Android 引用, onCancelled() 和 doInBackground() 之间的时间是明确定义的:

Calling this method will result in onCancelled(Object) being invoked on the UI thread after doInBackground(Object[]) returns. Calling this method guarantees that onPostExecute(Object) is never invoked

但是，查看我的 logcat，我可以看到 onCancelled() 方法在 doInBackground() 方法返回之前执行。

07-10 12:38:57.000: VERBOSE/AsyncTask(7473): doInBackground entered
07-10 12:38:57.000: VERBOSE/AsyncTask(7473): AsyncTask attempting to take the lock
07-10 12:38:57.000: VERBOSE/AsyncTask(7473): AsyncTask got the lock
07-10 12:38:57.420: VERBOSE/AsyncTask(7473): Start Item[0].state = 0
07-10 12:38:57.933: VERBOSE/AsyncTask(7473): onProgressUpdate entered
07-10 12:38:57.940: VERBOSE/AsyncTask(7473): onProgressUpdate exited
07-10 12:38:58.320: VERBOSE/(7473): onCancelListener cancelling AsyncTask
07-10 12:38:58.400: VERBOSE/AsyncTask(7473): onCancelled entered
07-10 12:38:58.400: VERBOSE/AsyncTask(7473): onCancelled exited
07-10 12:38:58.560: VERBOSE/AsyncTask(7473): Started checking file URL
07-10 12:38:58.601: VERBOSE/FileHost(7473): checkFile entered
07-10 12:38:58.641: VERBOSE/FileHost(7473): checkFile checking URI
07-10 12:38:58.691: DEBUG/dalvikvm(7473): threadid=19 wakeup: interrupted
07-10 12:38:58.710: VERBOSE/AsyncTask(7473): AsyncTask released the lock
07-10 12:38:58.710: VERBOSE/AsyncTask(7473): doInBackground exited

使用调试器并在 onCancelled() 方法和 doInBackground() 方法结束处设置断点，我还可以看到在 doInBackground() 结束之前调用了 onCancelled()。

是否有某种方式导致我在 AsyncTask 中错误编码某些内容，导致 Android 引用和我的应用程序行为之间存在这种行为差异？

编辑为 Gallal 添加一些代码:

@Gallal，Activity 包含这段代码。

private class OnCancelListener implements AddUrlDialog.CancelListener {
  @Override
  public void cancel() {
    if (addUrlInProgress == true) {
      addUrlInProgress = false;
      Log.v(TAG, "onCancelListener cancelling AsyncTask");
      addUrlControl.stopUpdates(true);
      AddUrlDialog.dismiss();
    }
  } 
}

AsyncTask.cancel 在 addUrlControl.stopUpdates() 方法中调用。

public void stopUpdates(boolean cleanupLists) {
  if (asyncTaskExited != true) {
      cancelRequest = true; 
        addUrlAsyncTask.cancel(true);
        //TEST httpRequest.abort(); // Also sends an abort to the HTTP request
  }
}

AsyncTask doInBackground 方法如下所示。

@Override
protected Void doInBackground(Void... v) {
  Log.v(TAG, "doInBackground entered");

    netConn = addUrlControl.myApp.getNetConn();
    client = netConn.getHttpClient();

    try {
      doInBackgroundBody();
  } catch (Throwable t) {
      Log.e(TAG, "doInBackgroundBody threw an exception: ", t);
  } finally {
      addUrlControl.myApp.releaseNetConn();
  }

    Log.v(TAG, "doInBackground exited");        
    return null;
}

Answer 1

我可以确认(正如你们中的一些人已经说过的那样)有一个 bug in the Android source for 2.x versions这使得 onCancelled() 在 cancel() 之后和 doInBackground() 完成之前被调用。

因此，如果您在 onCancelled() 中进行清理，您实际上会在 AsyncTask 运行的同时执行此操作，这会使您的应用程序崩溃!这让我们改变设计...

希望对您有所帮助!