Start AsyncTask in TimerTask

Question

I have a timer that I want to start an AsyncTask when the countdown is done. If I put the execution of it in a handler it loops it and starts it many times. And if I dont put it in a Handler I get the following crash: can't create handler inside thread that has not called looper.prepare()

timer.schedule(new ListUpdate(), helper.nextListUpdate.get(0));

class ListUpdate extends TimerTask {
    private Handler mHandler = new Handler(Looper.getMainLooper());
    public void run() {
        mHandler.post(new Runnable() {
            public void run() {
                AsyncTask<Integer, Void, Boolean> task = new updateList();
                task.execute();
            }
        });
    }
}

Any suggestions of how I can solve this?

Check [this one](http://stackoverflow.com/questions/6922561/how-to-update-listview-after-calling-asynctask-to-call-webservice/6922652#6922652) and get it working — Lalit Poptani, May 08 '12 at 10:22
The part that updates UI should be put inside `runOnUiThread()` — Lalit Poptani, May 08 '12 at 11:01
Same thing happens as before, it loads, and loads, and loads, and loads the AsyncTask. — just_user, May 08 '12 at 11:39
[come here as ask you will get your answer](http://chat.stackoverflow.com/rooms/1278/android-discussion) — Lalit Poptani, May 08 '12 at 11:44
you got this error because u can not update ur UI in Thread.u need to update UI from handler — Richa, May 08 '12 at 10:26
Yeah, but I need suggestions of how I can solve it, not why it happens! — just_user, May 08 '12 at 10:57

waqaslam · Answer 1 · 2012-05-08T10:28:43.817

5

AsyncTask is supposed to run on UI thread only. In your case, seems like you are not running it properly on a UI thread.

Perhaps try it like this:

timer.schedule(new ListUpdate(), helper.nextListUpdate.get(0));

class ListUpdate extends TimerTask {
    Looper looper = Looper.getMainLooper();
    looper.prepareMainLooper();

    private Handler mHandler = new Handler(looper);
    public void run() {
        mHandler.post(new Runnable() {
            public void run() {
                AsyncTask<Integer, Void, Boolean> task = new updateList();
                task.execute();
            }
        });
    }
}

edited May 08 '12 at 10:28

answered May 08 '12 at 10:22

waqaslam

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This results in the following error. But its the closest to make it work so far:Only the original thread that created a view hierarchy can touch its views. – just_user May 08 '12 at 10:54
then i would suggest you to skip `looper.prepareMainLooper();` and in Async's **doInBackground** method, call `Looper.prepare(); Looper.loop();` and see if it works. For more info read [this](http://stackoverflow.com/questions/6766002/android-difference-between-getmainlooper-and-looper-mylooper) – waqaslam May 08 '12 at 11:07
why use a timertask for this ? You have a handler, use it ! – njzk2 Nov 23 '12 at 11:10
timertask is for initiating something at some point in future and he was using handler. But the problem was that his handler wasn't attached to a looper that is looping on a UI thread and that is the reason he couldn't execute AsyncTask (because AsyncTasks only run on UI thread). I know its a little messy solution but the idea is to inform OP that you need a looper that loops on a UI thread :) – waqaslam Nov 23 '12 at 11:22

score 0 · Accepted Answer · answered May 09 '12 at 07:40

By adding a handler outside of the TimerTask which I call from the TimerTask I could make it work!

final Handler handler = new Handler() {
    public void handleMessage(Message msg) {
        RelativeLayout rl_header = (RelativeLayout)findViewById(R.id.rl_header);
        Desktop desktop = helper.getDesktop();
        try {
            desktop.inflate(ll, rl_header, banners, DesktopApp.this);
            Collections.sort(helper.nextListUpdate);
            helper.nextListUpdate.remove(0);
            timer = new Timer();
            if (helper.nextListUpdate.size() > 0) timer.schedule(new ListUpdate(), helper.nextListUpdate.get(0));
        } catch (Exception e) {
            e.printStackTrace();
        }
     }

};

class ListUpdate extends TimerTask {
    public void run() {
        DesktopApp.this.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                handler.sendEmptyMessage(0);
            }
        });
    }
}

why does everyone keeps using both timertasks and handlers ? — njzk2, Nov 23 '12 at 11:11

Start AsyncTask in TimerTask

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