AngularJS:使用异步数据初始化服务 [英] AngularJS : Initialize service with asynchronous data

问题描述

我有一个 AngularJS 服务，我想用一些异步数据对其进行初始化.像这样:

I have an AngularJS service that I want to initialize with some asynchronous data. Something like this:

myModule.service('MyService', function($http) {
    var myData = null;

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

    return {
        setData: function (data) {
            myData = data;
        },
        doStuff: function () {
            return myData.getSomeData();
        }
    };
});

显然这是行不通的，因为如果在 myData 返回之前尝试调用 doStuff()，我会得到一个空指针异常.据我从阅读此处 和 这里 我有几个选项，但似乎没有一个很干净(也许我遗漏了什么):

Obviously this won't work because if something tries to call doStuff() before myData gets back I will get a null pointer exception. As far as I can tell from reading some of the other questions asked here and here I have a few options, but none of them seem very clean (perhaps I am missing something):

使用run"设置服务

在设置我的应用时，请执行以下操作:

When setting up my app do this:

myApp.run(function ($http, MyService) {
    $http.get('data.json').success(function (data) {
        MyService.setData(data);
    });
});

然后我的服务看起来像这样:

Then my service would look like this:

myModule.service('MyService', function() {
    var myData = null;
    return {
        setData: function (data) {
            myData = data;
        },
        doStuff: function () {
            return myData.getSomeData();
        }
    };
});

这在某些时候是有效的，但是如果异步数据碰巧花费的时间比初始化所有内容所需的时间长，我在调用 doStuff()

This works some of the time but if the asynchronous data happens to take longer than it takes for everything to get initialized I get a null pointer exception when I call doStuff()

使用承诺对象

这可能会奏效.唯一的缺点是我调用 MyService 的所有地方我都必须知道 doStuff() 返回一个承诺，并且所有代码都必须让我们 then 与承诺进行交互.我宁愿等到 myData 恢复后再加载我的应用程序.

This would probably work. The only downside it everywhere I call MyService I will have to know that doStuff() returns a promise and all the code will have to us then to interact with the promise. I would rather just wait until myData is back before loading the my application.

手动引导

angular.element(document).ready(function() {
    $.getJSON("data.json", function (data) {
       // can't initialize the data here because the service doesn't exist yet
       angular.bootstrap(document);
       // too late to initialize here because something may have already
       // tried to call doStuff() and would have got a null pointer exception
    });
});

全局 Javascript 变量我可以将我的 JSON 直接发送到全局 Javascript 变量:

Global Javascript Var I could send my JSON directly to a global Javascript variable:

HTML:

<script type="text/javascript" src="data.js"></script>

data.js:

var dataForMyService = { 
// myData here
};

然后在初始化MyService时可用:

myModule.service('MyService', function() {
    var myData = dataForMyService;
    return {
        doStuff: function () {
            return myData.getSomeData();
        }
    };
});

这也可以，但是我有一个全局 javascript 变量，它闻起来很糟糕.

This would work too, but then I have a global javascript variable which smells bad.

这些是我唯一的选择吗?这些选项之一是否比其他选项更好?我知道这是一个很长的问题，但我想表明我已尝试探索所有选项.任何指导将不胜感激.

Are these my only options? Are one of these options better than the others? I know this is a pretty long question, but I wanted to show that I have tried to explore all my options. Any guidance would greatly be appreciated.

推荐答案

你有没有看过$routeProvider.when('/path',{ resolve:{...}? 它可以使 promise 方法更简洁:

Have you had a look at $routeProvider.when('/path',{ resolve:{...}? It can make the promise approach a bit cleaner:

在您的服务中公开承诺:

Expose a promise in your service:

app.service('MyService', function($http) {
    var myData = null;

    var promise = $http.get('data.json').success(function (data) {
      myData = data;
    });

    return {
      promise:promise,
      setData: function (data) {
          myData = data;
      },
      doStuff: function () {
          return myData;//.getSomeData();
      }
    };
});

将 resolve 添加到您的路由配置中:

Add resolve to your route config:

app.config(function($routeProvider){
  $routeProvider
    .when('/',{controller:'MainCtrl',
    template:'<div>From MyService:<pre>{{data | json}}</pre></div>',
    resolve:{
      'MyServiceData':function(MyService){
        // MyServiceData will also be injectable in your controller, if you don't want this you could create a new promise with the $q service
        return MyService.promise;
      }
    }})
  }):

在解决所有依赖项之前，您的控制器不会被实例化:

Your controller won't get instantiated before all dependencies are resolved:

app.controller('MainCtrl', function($scope,MyService) {
  console.log('Promise is now resolved: '+MyService.doStuff().data)
  $scope.data = MyService.doStuff();
});

我在 plnkr 做了一个例子:http://plnkr.co/edit/GKg21XH0RwCMEQGUdZKH?p=预览

I've made an example at plnkr: http://plnkr.co/edit/GKg21XH0RwCMEQGUdZKH?p=preview

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