AsyncTask 不会停止

Question

I've created an AsyncTask that loads messaging history from a database and then shows it on the device screen:

private void loadHistoryFromDB(Date lastUpdateDate)
    {
    final class DBAsyncTask extends AsyncTask<Void, Void, List<XMPPMessage>>
    {
        @Override
        protected List<XMPPMessage> doInBackground(Void... arg0) 
        {
            List<XMPPMessage> messages = null;
            try 
            {
                messages = PersistenceManager.getXMPPMessagesFromDB(userInfo, 0, messagingActivity);
            }
            catch (SQLException e) 
            {
                e.printStackTrace();
            } 
            catch (LetsDatabaseException e)
            {
                e.printStackTrace();
            }
            return messages;
        }

It seems to work fine, but after being executed, it leaves 2 running threads and I can't finish the activity because of that. How can I fix it?

Answer 1

As long as your tasks are executing properly (exits from onPostExecute ), this shouldn't be something you have to worry about. Once executed, AsyncTask thread(s) will stick around for possible reuse in the form of a thread pool or single thread, depending on platform version. This is normal behaviour - they will eventually be cleaned-up/reused.

Answer 2

This problem is most likely due to confusion surrounding the cancel method of AsyncTask.

You need to break down your background task into loopable segments, then Before each loop iteration starts doing your task,you need to check if the task is cancelled and if it is you need to break the loop. There doesn't seem to be any other way to stop an AsyncTask from executing.

I've posted a detailed guide to this problem with code examples here:

http://tpbapp.com/android-development/android-asynctask-stop-running-cancel-method/

Answer 3

First off, make sure you are calling super.doInBackGround() at the top of your overridden method call.

If that isn't it, it's likely because you are maintaining the connecting to the database.

That is, you still have a lock established on the database.

See if you can explicitly unlock the database, that may fix your problem.

You could put it in the onPostExecute() method.