使用$ injector与直接注入服务 [英] Using $injector vs injecting a service directly

问题描述

我想知道您何时使用$injector.get('someService')而不是直接注入该服务.

I was wondering when would you use $injector.get('someService') vs injecting that service directly.

基本上，下面的两个代码有什么区别?

Basically, what is the difference of the two code below?

angular
    .module('myApp')
    .controller('MyController', MyController);

/** Difference of this **/
MyController.$inject = ['$rootScope', '$route']; // and more services
MyController($rootScope, $route)
{
    /* ... */
}

/** And this **/
MyController.$inject = ['$injector'];
MyController($injector)
{
    var $rootScope = $injector.get('$rootScope');
    var $route     = $injector.get('$route');
    /* and so on */
}

如果不确定控制器需要什么，或者将来会更新它，并对其进行重构，则使用$injector可以轻松添加/删除依赖项.

If you are not sure what your controller needs, or that you will update it in the future, and you have it refactored, then using $injector it is a lot easier to add/remove dependencies.

推荐答案

第一种方法使用依赖项注入，第二种方法使用服务定位器模式.依赖注入具有以下优点:

The first approach uses dependency injection while the second uses service locator pattern. Dependency injection has the following advantages:

• 它使组件的依赖关系显式化.例如，您可以查看控制器的构造函数，并立即知道它需要什么依赖关系.使用服务定位器，您通常不知道，因为控制器可以随时调用服务定位器.

• It makes a component's dependencies explicit. For example, you can look at the constructor function of a controller and immediately know what dependencies it needs. With service locator, you usually have no idea because the controller might invoke the service locator any time.

这使单元测试更加容易.例如，您可以使用$controller服务实例化控制器，并通过locals参数将其提供给模拟对象.这肯定比必须定义一堆AngularJS服务或工厂要容易得多，以便$injector可以解析它们.与#1结合使用时，情况会变得更糟:您可能不知道组件才能提供所有必需的模拟所需的所有依赖关系.

It makes unit test easier. For example you can use the $controller service to instantiate a controller and feed it with mock objects via the locals argument. That's certainly easier than having to define a bunch of AngularJS services or factories so that $injector can resolve them. It becomes worse when coupled with #1: you might not be aware of all dependencies a component needs in order to supply all the necessary mocks.

服务定位器确实提供了一些灵活性思想.例如，您的代码可能仅在服务存在时才使用它，例如:

Service locator does offer some flexibility thought. For example, your code might use a service only if it exists, like this:

if ($injector.has('serviceA')) $injector.get('serviceA').doSomething() 
else someSomethingElse()

使用依赖项注入，如果在构造组件时不存在serviceA，则会出现错误.

With dependency injection, if serviceA doesn't exist by the time your component is constructed, you'll get an error.

为了便于重构，我认为向构造函数添加/删除参数并不困难.正如您对问题的评论所指出的那样，诸如ngAnnotate之类的工具将有助于使声明DRYer.

As to ease of refactoring, I don't think it's difficult to add/remove parameters to the constructor function. As pointed out in a comment to your question, tools like ngAnnotate will help make the declaration DRYer.

因此，我只坚持依赖注入，仅在绝对必要时才使用服务定位器.

Therefore, I would just stick with dependency injection and only use service locator when absolutely necessary.

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