Question

我试图找到答案并开始阅读承诺/延期，但是当从其他地方开始时，我不知道如何处理这个问题。

    angular.module('myapp.utilities').factory('codetabelService', ['Restangular', function(Restangular) {
    var initialized = false;
    var listtopopulate1 = [];
    var listtopopulate2 = [];

    var update = function() {
        Restangular.all('codeTabel').getList()
            .then(function(codetabellen) {
                codetabellen.forEach(function(entry) {
                    //do some processing on return values 
                    listtopopulate1.push(entry);
                    listtopopulate2.push(entry);
                });
                initialized=true;
            });
    };

    return {
        initialize: function() {
            if (!initialized) {
                update();
            }
        },
        getListValuesType1: function() {
            //How do I wait here for initialized to become true?
            return listtopopulate1;
        },
        getListValuesType2: function() {
            //How do I wait here for initialized to become true?
            return listtopopulate2;
        }
    };
}]);

因此，我尝试做的是在单页应用启动时缓存一些值。在我的根控制器上，我调用initialize方法，该方法启动对后端的异步调用。当我的视图被加载并且控制器将范围值设置为getListValuesType1（）的结果时，异步调用有时尚未完成。

因为调用方法getListValuesType1（）的控制器没有触发异步加载，所以我不确定promises是否适用于此（我承认，我还是新手）

我发现了you can put a timer on it，但这似乎并不合适。只是觉得那里有更好的解决方案。

Answer 1

是的，您可以有效地使用承诺和承诺缓存来实现此目的，通过以下方式实现此目的： -

angular.module('myapp.utilities').factory('codetabelService', ['Restangular', '$q', function(Restangular, $q) {

    var initialized;//Use this to cache the promise
    var listtopopulate1 = [];
    var listtopopulate2 = [];

    var _initialize = function() {
       //If already initialized just return it which is nothing but the promise. This will make sure initialization call is not made
       return initialized || (initialized= Restangular.all('codeTabel').getList()
            .then(function(codetabellen) {
                codetabellen.forEach(function(entry) {
                   listtopopulate1.push(entry);
                   listtopopulate2.push(entry);
                });
              //Note- You could even return the data here
            }, function(){
                //Just clean up incase call is a failure.
                initialized = null;
                //Just reject with something if you want to:-
                //return $q.reject("SomeError")
            }));
    };

    return {
        initialize: function() {
            return _initialize(); //Just return promise incase you want to do somthing after initialization
        },
        getListValuesType1: function() {
         return _initialize().then(function(){  //return promise with a chain that resolves to the list
            return listtopopulate1;
         });
        },
        getListValuesType2: function() {
         return _initialize().then(function(){ //return promise with a chain that resolves to the list
            return listtopopulate2;
         });
        }
    };
}]);

使用它时，您可以： -

codetabelService.getListValuesType1().then(function(list){
      $scope.list1 = list;
});

有了这个，您甚至可以从合同中删除initialize调用，并仅在首次使用getListX方法时进行ajax调用。

Answer 2

承诺将为此工作。你可能需要重构一些东西。

angular.module('myapp.utilities').factory('codetabelService', ['Restangular', function(Restangular) {
    var initialized = false;
    var listtopopulate1 = [];
    var listtopopulate2 = [];

    var update = function() {
        return Restangular.all('codeTabel').getList()
            .then(function(codetabellen) {
                codetabellen.forEach(function(entry) {
                    //do some processing on return values 
                    listtopopulate1.push(entry);
                    listtopopulate2.push(entry);
                });
                initialized=true;
            });
    };

    return {
        initialize: function() {
            if (!initialized) {
                this.updatePromise = update();
            }
        },
        getListValuesType1: function() {
            //How do I wait here for initialized to become true?
            return this.updatePromise.then(function() {
              // you'll want to refactor the callee to handle a promise here
              return listtopopulate1;              
            });
        },
        getListValuesType2: function() {
            return this.updatePromise.then(function(){
              // you'll want to refactor the callee to handle a promise here
              //How do I wait here for initialized to become true?
              return listtopopulate2;
            });
            //How do I wait here for initialized to become true?

        }
    };
}]);

等待异步调用在其他地方启动时返回

2 个答案: