为什么在Angular中使用服务？

>在控制器之间保持和共享数据.
IE：创建一个从数据库中获取数据的服务,如果将其存储在控制器中,一旦更改为另一个Controller,数据将被丢弃(除非您将它存储在$rootScope中,但这不是最好的方法它),但是如果您将其保留在服务(服务是单身)中,则在更改控制器时,数据将持续存在.
>抽象数据访问逻辑,通过创建一个API将被您的控制器/指令/服务使用.
将业务逻辑保持在服务内部的控制器和数据逻辑中.
> DRY(不要重复你自己).IE：你有一系列的功能需要在不同的控制器,没有服务,你不得不重复每个控制器的代码,一个服务,你可以创建一个单一的API为此功能并将其注入您需要的每个控制器/指令/服务.

这是一个例子：

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


//Here is the service Users with its functions and attributes
//You can inject it in any controller,service is a singleton and its data persist between controllers
myApp.factory('Users',function () {

    //data logic
    //fetch data from db and populate...
    var name = "John";
    var surname = "Doe" 

    function getName() { return name; }
    function getFullName() { return name + ' ' + surname; }
    function setName(newName) { name = newName; }

    //API
    return {
        getName: getName,getFullName: getFullName,setName: setName
    }
});

//An Util service with methods I will use in different controllers   
myApp.factory('Util',function () {

    //a bunch of useful functions I will need everywhere
    function daysInMonth (month,year) {
        return new Date(year,month+1,0).getDate();
    }

    return {
        daysInMonth: daysInMonth    
    };
});   

//Here I am injecting the User and Util services in the controllers   
myApp.controller('MyCtrl1',['$scope','Users','Util',function ($scope,Users,Util) {

    $scope.user = Users.getFullName(); //"John Doe";
    Users.setName('Bittle');

    //Using Util service
    $scope.days = Util.daysInMonth(05,2013);
}]);

myApp.controller('MyCtrl2',Util) {

    $scope.user = Users.getFullName(); //"Bittle Doe"; //The change that took place in MyCtrl1 hhas persisted.

}]);