你能在返回之前解决一个 angularjs 承诺吗？

Question

我正在尝试编写一个返回承诺的函数。但有时要求的信息会立即可用。我想把它包装在一个承诺中，这样消费者就不需要做出决定了。

function getSomething(id) {
    if (Cache[id]) {
        var deferred = $q.defer();
        deferred.resolve(Cache[id]); // <-- Can I do this?
        return deferred.promise;
    } else {
        return $http.get('/someUrl', {id:id});
    }
}

并像这样使用它：

somethingService.getSomething(5).then(function(thing) {
    alert(thing);
});

问题是回调没有为预先解决的承诺执行。这是合法的做法吗？有没有更好的方法来处理这种情况？

Answer 1

如何在 Angular 1.x 中简单地返回一个预先解决的承诺

已解决的承诺：

return $q.when( someValue );    // angular 1.2+
return $q.resolve( someValue ); // angular 1.4+, alias to `when` to match ES6

被拒绝的承诺：

return $q.reject( someValue );

Answer 2

简短回答：是的，您可以在返回 AngularJS 承诺之前解决它，它的行为会如您所愿。

来自JB Nizet's Plunkr，但经过重构以在最初询问的内容（即对服务的函数调用）和实际在现场的上下文中工作。

服务内部...

function getSomething(id) {
    // There will always be a promise so always declare it.
    var deferred = $q.defer();
    if (Cache[id]) {
        // Resolve the deferred $q object before returning the promise
        deferred.resolve(Cache[id]); 
        return deferred.promise;
    } 
    // else- not in cache 
    $http.get('/someUrl', {id:id}).success(function(data){
        // Store your data or what ever.... 
        // Then resolve
        deferred.resolve(data);               
    }).error(function(data, status, headers, config) {
        deferred.reject("Error: request returned status " + status); 
    });
    return deferred.promise;

}

在控制器内部....

somethingService.getSomething(5).then(    
    function(thing) {     // On success
        alert(thing);
    },
    function(message) {   // On failure
        alert(message);
    }
);

我希望它对某人有所帮助。我没有发现其他答案很清楚。

Answer 3

我喜欢使用工厂从我的资源中获取数据。

.factory("SweetFactory", [ "$http", "$q", "$resource", function( $http, $q, $resource ) {
    return $resource("/sweet/app", {}, {
        "put": {
            method: "PUT",
            isArray: false
        },"get": {
            method: "GET",
            isArray: false
        }
    });
}]);

然后在这里像这样在服务中公开我的模型

 .service("SweetService",  [ "$q", "$filter",  "$log", "SweetFactory",
    function ($q, $filter, $log, SweetFactory) {

        var service = this;

        //Object that may be exposed by a controller if desired update using get and put methods provided
        service.stuff={
            //all kinds of stuff
        };

        service.listOfStuff = [
            {value:"", text:"Please Select"},
            {value:"stuff", text:"stuff"}];

        service.getStuff = function () {

            var deferred = $q.defer();

          var promise = SweetFactory.get().$promise.then(
                function (response) {
                    if (response.response.result.code !== "COOL_BABY") {
                        deferred.reject(response);
                    } else {
                        deferred.resolve(response);
                        console.log("stuff is got", service.alerts);
                        return deferred.promise;
                    }

                }
            ).catch(
                function (error) {
                    deferred.reject(error);
                    console.log("failed to get stuff");
                }
            );

            promise.then(function(response){
                //...do some stuff to sett your stuff maybe fancy it up
                service.stuff.formattedStuff = $filter('stuffFormatter')(service.stuff);

            });


            return service.stuff;
        };


        service.putStuff = function () {
            console.log("putting stuff eh", service.stuff);

            //maybe do stuff to your stuff

            AlertsFactory.put(service.stuff).$promise.then(function (response) {
                console.log("yep yep", response.response.code);
                service.getStuff();
            }).catch(function (errorData) {
                alert("Failed to update stuff" + errorData.response.code);
            });

        };

    }]);

然后我的控制器可以简单地通过引用注入的 Service.whatever 来包含它并公开它或在其上下文中做正确的事情

似乎工作正常。但我对角度有点陌生。 *为了清晰起见，大部分都省略了错误处理

Answer 4

如果我想在数组或对象中实际缓存数据，我通常会这样做

app.factory('DataService', function($q, $http) {
  var cache = {};
  var service= {       
    getData: function(id, callback) {
      var deffered = $q.defer();
      if (cache[id]) {         
        deffered.resolve(cache[id])
      } else {            
        $http.get('data.json').then(function(res) {
          cache[id] = res.data;              
          deffered.resolve(cache[id])
        })
      }
      return deffered.promise.then(callback)
    }
  }

  return service

})

DEMO

Answer 5

你忘记初始化缓存元素

function getSomething(id) {
    if (Cache[id]) {
        var deferred = $q.defer();
        deferred.resolve(Cache[id]); // <-- Can I do this?
        return deferred.promise;
    } else {
        Cache[id] = $http.get('/someUrl', {id:id});
        return Cache[id];
    }
}