AngularJS 依赖注入
依赖注入是一种软件设计，在这种设计中，组件被赋予了依赖关系，而不是在组件内对其进行硬编码。它使组件免于定位依赖项并使依赖项可配置。它还有助于使组件可重用、可维护和可测试。
AngularJS 提供了最高的依赖注入机制。它提供了以下核心组件，这些组件可以作为依赖项相互注入。
Value
Factory
Service
Provider
Constant
Value 是一个简单的 JavaScript 对象，需要在配置阶段将值传递给控制器（配置阶段是 AngularJS 引导自身的时候）。
//define a module
var mainApp = angular.module("mainApp", []);
//create a value object as "defaultInput" and pass it a data.
mainApp.value("defaultInput", 5);
...
//inject the value in the controller using its name "defaultInput"
mainApp.controller('CalcController', function($scope, CalcService, defaultInput) {
$scope.number = defaultInput;
$scope.result = CalcService.square($scope.number);
$scope.square = function() {
$scope.result = CalcService.square($scope.number);
}
});
工厂
Factory 是一个用于返回值的函数。只要服务或控制器需要它，它就会按需创造价值。它一般使用工厂函数来计算和返回值。
//define a module
var mainApp = angular.module("mainApp", []);
//create a factory "MathService" which provides a method multiply to return multiplication of two numbers
mainApp.factory('MathService', function() {
var factory = {};
factory.multiply = function(a, b) {
return a * b
}
return factory;
});
//inject the factory "MathService" in a service to utilize the multiply method of factory.
mainApp.service('CalcService', function(MathService) {
this.square = function(a) {
return MathService.multiply(a,a);
}
});
...
服务
Service 是一个单例 JavaScript 对象，包含一组执行特定任务的函数。使用 service() 函数定义服务，然后将其注入控制器。
//define a module
var mainApp = angular.module("mainApp", []);
...
//create a service which defines a method square to return square of a number.
mainApp.service('CalcService', function(MathService) {
this.square = function(a) {
return MathService.multiply(a,a);
}
});
//inject the service "CalcService" into the controller
mainApp.controller('CalcController', function($scope, CalcService, defaultInput) {
$scope.number = defaultInput;
$scope.result = CalcService.square($scope.number);
$scope.square = function() {
$scope.result = CalcService.square($scope.number);
}
});
供应商
Provider 在配置阶段被 AngularJS 内部用来创建服务、工厂等。以下脚本可用于创建我们之前创建的 MathService。 Provider 是一个特殊的工厂方法，带有 get() 方法，用于返回值/服务/工厂。
//define a module
var mainApp = angular.module("mainApp", []);
...
//create a service using provider which defines a method square to return square of a number.
mainApp.config(function($provide) {
$provide.provider('MathService', function() {
this.$get = function() {
var factory = {};
factory.multiply = function(a, b) {
return a * b;
}
return factory;
};
});
});
常数
考虑到无法在配置阶段使用值，常量用于在配置阶段传递值。
mainApp.constant("configParam", "constant value");
示例
以下示例显示了上述所有指令的使用-
testAngularJS.htm
<html>
<head>
<title>AngularJS Dependency Injection</title>
</head>
<body>
<h2>AngularJS Sample Application</h2>
<div ng-app = "mainApp" ng-controller = "CalcController">
<p>Enter a number: <input type = "number" ng-model = "number" /></p>
<button ng-click = "square()">X<sup>2</sup></button>
<p>Result: {{result}}</p>
</div>
<script src = "https://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js">
</script>
<script>
var mainApp = angular.module("mainApp", []);
mainApp.config(function($provide) {
$provide.provider('MathService', function() {
this.$get = function() {
var factory = {};
factory.multiply = function(a, b) {
return a * b;
}
return factory;
};
});
});
mainApp.value("defaultInput", 5);
mainApp.factory('MathService', function() {
var factory = {};
factory.multiply = function(a, b) {
return a * b;
}
return factory;
});
mainApp.service('CalcService', function(MathService) {
this.square = function(a) {
return MathService.multiply(a,a);
}
});
mainApp.controller('CalcController', function($scope, CalcService, defaultInput) {
$scope.number = defaultInput;
$scope.result = CalcService.square($scope.number);
$scope.square = function() {
$scope.result = CalcService.square($scope.number);
}
});
</script>
</body>
</html>
