MVVMCross IMvxGeoLocationWatcher Success Action never fires on Android

问题

I created a very simple test app to try and reverse geocode my current lat/long into an address.

Here is the code for my ViewModel:

namespace LoginProductsMVVM.Core.ViewModels
{
    public class ProductDetailViewModel
        : MvxViewModel
    {
        public void Init(Product product)
        {
            Product = product;
        }

        private Product _product;
        public Product Product
        {
            get { return _product; }
            set { _product = value;
                RaisePropertyChanged (() => Product); }
        }

        private string _latitude;
        public string Latitude{
            get { return _latitude; }
            set { _latitude = value; RaisePropertyChanged(() => Latitude); }
        }

        private string _longitude;
        public string Longitude{
            get { return _longitude; }
            set { _longitude = value; RaisePropertyChanged(() => Longitude); }
        }

        private string _address;
        public string Address{
            get { return _address; }
            set { _address = value; RaisePropertyChanged(() => Address); }
        }

        private IMvxGeoLocationWatcher _watcher;
        public IMvxGeoLocationWatcher Watcher
        {
            get 
            {
                _watcher = Mvx.Resolve<IMvxGeoLocationWatcher> ();
                return _watcher;
            }
        }

        public ProductDetailViewModel(IMvxGeoLocationWatcher watcher)
        {
            _watcher = watcher;
            _watcher.Start (new MvxGeoLocationOptions (), OnLocation, OnError);
        }

        void OnLocation (MvxGeoLocation location)
        {
            Latitude = location.Coordinates.Latitude.ToString();
            Longitude = location.Coordinates.Longitude.ToString();

            // Android Location specific stuff
            var activity = Mvx.Resolve<IMvxAndroidCurrentTopActivity> ().Activity;
            Geocoder geocdr = new Geocoder (activity.BaseContext);

            IList<Address> addresses = geocdr.GetFromLocation (double.Parse(Latitude), double.Parse(Longitude), 1);

            addresses.ToList().ForEach ((addr) => Address += addr.ToString() + "\r\n\r\n");
        }

        void OnError (MvxLocationError error)
        {
            Mvx.Error ("Seen location error {0}", error);
        }
    }
}

I have a break point in my OnLocation method but it never gets in there. Am I missing something for this to work properly on Android? It appears to work just fine for iOS...

回答1:

Per Odahan here:

Well... I investigated a bit more : The problem is known and can be seen on many devices. This is not a MvvmCross problem. Short answer : the device needs to be rebooted and all is working like a charm... It seems Google sent some updates that are causing the problem. Here is a thread speaking about this problem and a similar one concerning the GeoCode class :

https://code.google.com/p/android/issues/detail?id=38009

So : can be closed, MvvmCross is ok but others can face this bug so my explanations and the link here.

回答2:

When you say it never fires 'success', does the success actually ever occur?

There could be lots of things going wrong in the GPS code - eg your app might not have privilege, your phone might have A-GPS or GPS disabled, or you might even be running on a location-less emulator - all of this is possible from your description.

It'a also worth noting that Xamarin.Android has long standing issues with hitting breakpoints - so it's better to add trace than to rely on breakpoint hitting :/

---

Perhaps try running though N=8 from http://mvvmcross.wordpress.com/ - does that help at all? (N=9 is also worth watching as it shows one way to allow multiple viewmodels to use the geowatcher)

来源：https://stackoverflow.com/questions/17703427/mvvmcross-imvxgeolocationwatcher-success-action-never-fires-on-android