If the AsyncTask finishes executing, the thread on which the asynctask
was run just waits (Object.wait()).
The AsyncTask is based upon the ExecutorService and FutureTask classes
from the java.util.concurrent packages.
Creating a new AsyncTask does not create a new thread. An AsyncTask is
executed on one thread selected from a pool of threads (internally it
uses ExecutorService from java.util.concurrent)
If you want to have ONE thread that continuously runs in the
background (e.g. wait 5 mins, see if there's data, if so notify the
main app, start over again), use a Thread, not an AsyncTask. When you
have a 'while(true)' or some similar loop in your background-task
code, it may be a sign that you need a Thread instead.
Then in that Thread you can have a reference to your activity (e.g.
mActivity) and call runOnUiThread() on your activity. Here is a code-
example snippet from that Thread:
public void run() {
while (!mStopped) {
sleep(fiveMinutes);
final Result result = getSomeDataFromSomehwere();
if (result.isNotEmpty()) {
mActivity.runOnUiThread(new Runnable() {
public void run() {
mActivity.hereIsResult(result);
}
});
}
}
}
(above is pseudo-code... it won't compile :-))
(and i assume that mActivity is still around and kicking when
hereIsResult is called... if not, you have to use a static reference
to your currently running activity instead)
On Jan 22, 6:38 pm, Flapjack <millerhugg...@gmail.com> wrote:
> Streets of Boston, please forgive my ignorance. If I use AsyncTask
> within a service to retrieve data once, can I destroy the AsyncTask
> after? Or would I have to destroy the entire Service?
>
> Additionally, if I want to poll, say, every 5 minutes, wouldn't having
> AsyncTask in the service be a good idea, instead of tying up the
> Service, which might be needed for other operations?
>
> Finally, what do you mean when you said to use a regular Thread that
> calls 'post' on the owning Activity?
>
> On Jan 21, 10:37 pm, Streets Of Boston <flyingdutc...@gmail.com>
> wrote:
>
>
>
> > A Service, like an Activity, has a main thread with a message-loop.
> > You can create an AsyncTask in the onXXXXX() callbacks of Services,
> > just like in an Activity. The onPostExecute can do your handling of
> > the results, as you described.
>
> > However, AsyncTask is more geared towards the one-time executing of a
> > background process. E.g. retrieve some data from the internet now, or
> > create/process a bitmap. It is not really meant to stay in the
> > background forever in a loop polling for some data to come in. When
> > you have something like 'while (true)' or 'while (!mStopped)' or
> > something like it, you should not use a AsyncTask. Use a regular
> > Thread instead that calls 'post' on the owning Activity that will
> > consume the results generated by the thread.
>
> > On Jan 21, 6:22 pm, Flapjack <millerhugg...@gmail.com> wrote:
>
> > > According to my research, which includes reputable sources (Mark
> > > Murphy et al), the most preferred way of polling a remote source and
> > > presenting said data to the user is by creating a service and using
> > > AsyncTask within that service to do the polling. I have done that.
>
> > > But, when I read the docs (http://developer.android.com/reference/
> > > android/os/AsyncTask.html), there seem to be several "Threading Rules"
> > > that conflict with this way of doing things: "The task instance must
> > > be created on the UI thread." and "execute(Params...) must be invoked
> > > on the UI thread." As stated, I have created the task instance on the
> > > Service thread (not the UI thread). Am I missing something?
>
> > > Also, when the AsyncTask finished, I sent out a Broadcast on
> > > onPostExecute, which is then picked up by the Activity, telling it to
> > > retrieve the final value again from the service (since I couldn't
> > > obviously update the UI from the service). I couldn't figure out any
> > > other way to return the result of the AsyncTask. Is this the correct
> > > practice?
>
> > > Java is not my native language so please bear with my ignorance.
> > > Thanks!- Hide quoted text -
>
> - Show quoted text -
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