Android: "Calling thread must be a prepared Looper thread" error when I use AsyncTask

Question

I've created a AsyncTask to retrieve a GPS position with a 20-meter accuracy. I would like to execute a while do cycle until accuracy is accetable.

The problem is that I got an exception when I request an update of position.

java.lang.NullPointerException: Calling thread must be a prepared Looper thread.

This is the piece of code that goes in error

@Override
protected String doInBackground(Void... params) {
if (ActivityCompat.checkSelfPermission(activity, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(activity, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                return null;
            }
            mLocationRequest.setInterval(100);
            mLocationRequest.setPriority(100);
            mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
            while (mLastLocation == null || (mLastLocation.getAccuracy()>Float.parseFloat("20.0") && mLastLocation.hasAccuracy())){
                try {
                    LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,activity);
                    mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
                } catch (SecurityException secex) {

                }
            }

            return null;
        }

Answer 1

I had troubles with this a full work day. I have the FusedLocationApi running in background within a Service.

What I a did -I read it somewhere else- is add Looper.getMainLooper() as the last parameter of requestLocationUpdates().

So, instead of this

LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,activity);

You'll have

LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this, Looper.getMainLooper());

If your read the whole FusedLocationProviderApi page, you will see that the method will do different thing depending on the parameters.