我开发一个小AngularJS应用程序，我目前正在创建一个服务中挣扎。

I'm developing a small AngularJS app and I'm currently struggling with creating a service.

我有作为用于提供触点的后端（姓名，地址...）的服务。到现在为止，他们硬codeD作为服务（ instance.contacts = [...] ）的数组，但现在我想读他们从JSON文件：

I have a service that serves as a backend for providing contacts (name, address...). Until now they were hard-coded as an array in the service (instance.contacts=[...]), but now I'm trying to read them from a json file :

myModule.factory('contactService', ['$http',function ($http) {
    var instance = {};

    $http.get('contacts.json').success(function (data) {
        instance.contacts = data;
    });

    return instance;
}]);

我看到，该文件已经被成功读取我的浏览器控制台，但我看不到屏幕上的任何变化。

所以，我想下面的，而是和它的工作：

So I tried the following instead, and it worked :

myModule.factory('contactService', ['$http',function ($http) {
    var instance = {
        contacts:[]
    };

    $http.get('contacts.json').success(function (data) {
        angular.forEach(data, function(item) {
            instance.contacts.push(item);
        });
    });

    return instance;
}]);

我不知道为什么第二code片段的作品，而不是第一个。可能有人请帮助我理解？

I don't know why the second code snippet works, and not the first. Could someone please help me understand ?

推荐答案

$ HTTP 是异步的，所以你不能返回数组，因为当你回来时，它可能不会有它的任何数据。实际上，你必须退回承诺：

$http is asynchronous, so you can't return an array because when you return it, it probably doesn't have any data in it yet. You actually have to return the promise:

var instance = $http('contacts.json');

return instance;

然后在你的控制器（或其他服务）：

And then in your controller (or in another service):

contactService.then(function(response) {
  $scope.contacts = response.data;
});

请记住，无论你在哪里访问你的服务，你必须用它作为一个承诺使用交互然后。