javascript - 连接 promise ，或者一个 promise 触发另一个 promise

Question

我正在构建一个天气应用程序，我首先必须获取用户位置，然后发出获取天气的请求。

所以我有一个 GeolocationService 和一个 WeatherService。我的 WeatherService 当前正在调用 Geolocation 服务。如何让 WeatherService 等到收到 GeolocationService 的结果后才发出 HTTP 请求？

  app.factory('GeolocationService',function($q,$window,$rootScope){        return {            getLatLon: function(){                var deferred = $q.defer();                if(!window.navigator){                    $rootScope.$apply(function(){                        deferred.reject(new Error("Geolocation not available"));                    });                } else {                    $window.navigator.geolocation.getCurrentPosition(function(position){                        $rootScope.$apply(function(){                            deferred.resolve(position);                        });                    }, function(error){                        $rootScope.$apply(function(){                            deferred.reject(error);                        });                    });                }                return deferred.promise;            }        };    });    app.factory("WeatherService", function ($q,$http,$rootScope, GeolocationService) {        return {            getWeather: function(){                var weather;                var loc = new GeolocationService.getLatLon();                 var  lat= loc.lat || 37.4568202221774,                 lon= loc.lon || -122.201366838789 ;                var units = '';                var url = 'http://api.openweathermap.org/data/2.5/forecast/daily?lat='+lat+'&lon='+lon+'&units='+units+'&callback=JSON_CALLBACK';                $http.jsonp(url)                    .success(function(data) {                        weather=data;                        return weather;                    })                    .error(function(err){                        weather=err;                        return err;                    });            }        };    });

Answer 1

您只需要在服务中使用 promise ，然后链接 promise 。例如，我有一个带有 user.company_id 的用户，如果我想获取公司名称，我必须等待用户加载。跟你的情况是一样的。

这是我的服务:

    angular.module('UserService', []) 
.factory('UserService', function($q , $http, $rootScope,$timeout) {
var currentUserPromise = null;
var currentCompanyPromise = null;
return {
    getCurrentUser: function() {
        if (currentUserPromise === null) {
            var config = {};
            config.cache = true;
            config.method = "GET"; 
            config.url = "users/get_current_user";
            currentUserPromise = $http(config)
                .then(function(response) {
                    if (typeof response.data === 'object') {
                        return response.data.user;
                    } else {
                        // invalid response
                        return $q.reject(response.data);
                    }  
                }, function(response) {
                    // something went wrong
                    return $q.reject(response.data);
                });
        }
        return currentUserPromise;
    },

    getCurrentCompany: function(company_id) {
        if (currentCompanyPromise === null){
            var config = {};
            var company = {};
            company.id = company_id; 
            config.cache = true;
            config.method = "GET"; 
            config.url = "/companies/show";
            config.params = company;
            currentCompanyPromise = $http(config)
                .then(function(response) {
                    if (typeof response.data === 'object') {
                        return response.data.company;
                    } else {
                        // invalid response
                        return $q.reject(response.data);
                    }

                }, function(response) {
                    // something went wrong
                    return $q.reject(response.data);
                });
            }
            return currentCompanyPromise;

        }
    };     
});

在我的 Controller 中我这样使用:

Controller :

var promiseCurrentUser = UserService.getCurrentUser();
promiseCurrentUser.then(function(user) {
    $scope.currentUser = user;
    UserService.getCurrentCompany(user.company_id).then(function(company){
        $scope.companyName = company.name;
    });
});

Promise 的最酷之处在于它一次性解决。

希望这对您有帮助。