角$ q嵌套承诺

Question

I have a function that needs to return a list of favorite locations. Something like this

LocationsFactory.getFavoriteLocations().then(function($favoriteLocations) { });

The getFavoriteLocations looks something like this

getFavoriteLocations: function() {
                if (favorite_locations.length == 0)
                {
                    var deff = $q.defer();
                    obj.getDeviceId().then(function(device_id) {
                    $http.get('url?token=' + device_id).then(function(response) {
                                 favorite_locations = response.data;
                                 deff.resolve(favorite_locations);
                                 return deff.promise;
                               })
                    })
                } else {
                    return favorite_locations;
                }
            }

The getDeviceId again, it's a function based on promise.

getDeviceId: function() {
  var deff = $q.defer();
  deff.resolve(Keychain.getKey());
  return deff.promise;
}

The error that I got is TypeError: Cannot read property 'then' of undefined. Please help!

Answer 1

$q in not necessary here:

if (favorite_locations.length == 0)
{
    return obj.getDeviceId() // you have to return a promise here
        .then(function(device_id) { 
            return $http.get('url?token=' + device_id) // you will access the response below
        })
        .then(function(response) {
            favorite_locations = response.data;
            return favorite_locations
        });
    })
}

Now it should work.

Answer 2

You can chain promises:

        getFavoriteLocations: function () {
            if (favorite_locations.length === 0) {
                return obj.getDeviceId().then(function (device_id) {
                    return $http.get('url?token=' + device_id).then(function (response) {
                         favorite_locations = response.data;
                         return favorite_locations;
                    });
                });
            }

            return $q.resolve(favorite_locations);
        }

And improve this:

getDeviceId: function() {
    return $q.resolve(Keychain.getKey());
}