AsyncTask and Looper.prepare() error

问题

I have the following code

class OverlayTask extends AsyncTask<Void, Void, Void> {
    @Override
    public void onPreExecute() {

        if (sites != null) {
            myMapView.getOverlays().remove(sites);
            myMapView.invalidate();
            sites = null;
        }
    }

    @Override
    public Void doInBackground(Void... unused) {
            grabShipsWithLocation();
            return (null);
    }

    @Override
    public void onPostExecute(Void unused) {
        myMapView.getOverlays().add(sites);
        myMapView.invalidate();
        isLoading = false;
    }
}

That seems to work fine on a few test devices but I am seeing a lot of errors appearing on the dev console. I can\'t seem to work out why and where to put this Looper.prepare(). Is it needed?

java.lang.ExceptionInInitializerError
at com.test.appname.FinderMain$1.gotLocation(FinderMain.java:286)
at com.test.appname.MyLocation$GetLastLocation.run(MyLocation.java:89)
at java.util.Timer$TimerImpl.run(Timer.java:289)
Caused by: java.lang.RuntimeException: Can\'t create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:121)
at android.os.AsyncTask$InternalHandler.<init>(AsyncTask.java:421)
at android.os.AsyncTask$InternalHandler.<init>(AsyncTask.java:421)
at android.os.AsyncTask.<clinit>(AsyncTask.java:152)

As requested MyLocation.java

    class GetLastLocation extends TimerTask {
    @Override
    public void run() {
         lm.removeUpdates(locationListenerGps);
         lm.removeUpdates(locationListenerNetwork);

         Location net_loc=null, gps_loc=null;
         if(gps_enabled)
             gps_loc=lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
         if(network_enabled)
             net_loc=lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

         //if there are both values use the latest one
         if(gps_loc!=null && net_loc!=null){
             if(gps_loc.getTime()>net_loc.getTime())
                 locationResult.gotLocation(gps_loc);
             else
                 locationResult.gotLocation(net_loc);
             return;
         }

         if(gps_loc!=null){
             locationResult.gotLocation(gps_loc); //Line 89
             return;
         }
         if(net_loc!=null){
             locationResult.gotLocation(net_loc);
             return;
         }
         locationResult.gotLocation(null);
    }
}

回答1:

Long story:

AsyncTask internally uses a Handler. A handler basically allows you to post Runnables from another thread on the thread the handler was assigned to, which in the case of AsyncTask is always the thread from which it is called. This only works for threads that have a Looper prepared, though.

For more information see http://developer.android.com/reference/android/os/Handler.html

Short story:

Simply wrap every call to FinderMain$1.gotLocation or the creation of AsyncTask within it in a Runnable, and post it to a Handler bound to the UI thread, like this:

class GetLastLocation extends TimerTask {
    private Handler mHandler = new Handler(Looper.getMainLooper());

    @Override
    public void run() {
       // ...
       mHandler.post(new Runnable() {
          public void run() {
              locationResult.gotLocation(null);
          }
       });
       // ...
     }
}

回答2:

I tried this...It worked,hope it will help you..

protected class Asyctast extends AsyncTask<String, Integer, Integer>
{

    @Override
    protected Integer doInBackground(String... params) {
        // TODO Auto-generated method stub


        Log.d("Asynctask", ""+params);  
Looper.prepare();   

         ImageThumbnailsActivity m = new ImageThumbnailsActivity();

            Toast.makeText(ImageThumbnailsActivity.this,""+params ,Toast.LENGTH_SHORT).show();
            final Dialog dialog_options = new Dialog(ImageThumbnailsActivity.this);
            dialog_options.setContentView(R.layout.option);
            dialog_options.show();
        Looper.loop();
        return null;
    }       
}

来源：https://stackoverflow.com/questions/4187960/asynctask-and-looper-prepare-error

标签

android

android-asynctask

looper