对于那些像我一样只是寻找一个简单的解决方案，这几乎完全是你所期望的在控制器中使用正常的$watch。 唯一的区别是，它在javascript上下文中计算字符串，而不是在特定的作用域上。您必须将$rootScope注入到您的服务中，尽管它只用于正确地钩子到摘要周期中。

function watch(target, callback, deep) {
    $rootScope.$watch(function () {return eval(target);}, callback, deep);
};

当我面对一个非常相似的问题时，我观察了一个作用域中的函数，并让函数返回服务变量。我已经创建了一个js小提琴。您可以在下面找到代码。

    var myApp = angular.module("myApp",[]);

myApp.factory("randomService", function($timeout){
    var retValue = {};
    var data = 0;

    retValue.startService = function(){
        updateData();
    }

    retValue.getData = function(){
        return data;
    }

    function updateData(){
        $timeout(function(){
            data = Math.floor(Math.random() * 100);
            updateData()
        }, 500);
    }

    return retValue;
});

myApp.controller("myController", function($scope, randomService){
    $scope.data = 0;
    $scope.dataUpdated = 0;
    $scope.watchCalled = 0;
    randomService.startService();

    $scope.getRandomData = function(){
        return randomService.getData();    
    }

    $scope.$watch("getRandomData()", function(newValue, oldValue){
        if(oldValue != newValue){
            $scope.data = newValue;
            $scope.dataUpdated++;
        }
            $scope.watchCalled++;
    });
});

如果您想避免$watch的暴政和开销，您总是可以使用老式的观察器模式。

在服务中:

factory('aService', function() {
  var observerCallbacks = [];

  //register an observer
  this.registerObserverCallback = function(callback){
    observerCallbacks.push(callback);
  };

  //call this when you know 'foo' has been changed
  var notifyObservers = function(){
    angular.forEach(observerCallbacks, function(callback){
      callback();
    });
  };

  //example of when you may want to notify observers
  this.foo = someNgResource.query().$then(function(){
    notifyObservers();
  });
});

在控制器中:

function FooCtrl($scope, aService){
  var updateFoo = function(){
    $scope.foo = aService.foo;
  };

  aService.registerObserverCallback(updateFoo);
  //service now in control of updating foo
};

您可以在工厂内部观察更改，然后广播更改

angular.module('MyApp').factory('aFactory', function ($rootScope) {
    // Define your factory content
    var result = {
        'key': value
    };

    // add a listener on a key        
    $rootScope.$watch(function () {
        return result.key;
    }, function (newValue, oldValue, scope) {
        // This is called after the key "key" has changed, a good idea is to broadcast a message that key has changed
        $rootScope.$broadcast('aFactory:keyChanged', newValue);
    }, true);

    return result;
});

然后在你的控制器中:

angular.module('MyApp').controller('aController', ['$rootScope', function ($rootScope) {

    $rootScope.$on('aFactory:keyChanged', function currentCityChanged(event, value) {
        // do something
    });
}]);

通过这种方式，您将所有相关的工厂代码放在其描述中，然后您只能依赖来自外部的广播

没有手表或观察者回调(http://jsfiddle.net/zymotik/853wvv7s/):

JavaScript:

angular.module("Demo", [])
    .factory("DemoService", function($timeout) {

        function DemoService() {
            var self = this;
            self.name = "Demo Service";

            self.count = 0;

            self.counter = function(){
                self.count++;
                $timeout(self.counter, 1000);
            }

            self.addOneHundred = function(){
                self.count+=100;
            }

            self.counter();
        }

        return new DemoService();

    })
    .controller("DemoController", function($scope, DemoService) {

        $scope.service = DemoService;

        $scope.minusOneHundred = function() {
            DemoService.count -= 100;
        }

    });

HTML

<div ng-app="Demo" ng-controller="DemoController">
    <div>
        <h4>{{service.name}}</h4>
        <p>Count: {{service.count}}</p>
    </div>
</div>

这个JavaScript在我们从服务返回一个对象而不是一个值时工作。当一个JavaScript对象从服务返回时，Angular会向它的所有属性中添加手表。

还要注意，我使用'var self = this'，因为我需要在$timeout执行时保持对原始对象的引用，否则'this'将引用窗口对象。

有点丑，但我已经为切换添加了范围变量的注册到我的服务:

myApp.service('myService', function() {
    var self = this;
    self.value = false;
    self.c2 = function(){};
    self.callback = function(){
        self.value = !self.value; 
       self.c2();
    };

    self.on = function(){
        return self.value;
    };

    self.register = function(obj, key){ 
        self.c2 = function(){
            obj[key] = self.value; 
            obj.$apply();
        } 
    };

    return this;
});

然后在控制器中:

function MyCtrl($scope, myService) {
    $scope.name = 'Superhero';
    $scope.myVar = false;
    myService.register($scope, 'myVar');
}