AngularJS - 依赖注入( Dependency Injection)
依赖注入是一种软件设计，其中组件被赋予其依赖性，而不是在组件内对它们进行硬编码。 它减轻了组件定位依赖关系并使依赖关系可配置。 它还有助于使组件可重用，可维护和可测试。
AngularJS提供了一种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互相注入。
- Value
- Factory
- Service
- Provider
- Constant
Value
Value是一个简单的JavaScript对象，在配置阶段需要将值传递给控制器（配置阶段是AngularJS引导自身时）。
//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);
}
});
Factory
Factory是一个用于返回值的函数。 只要服务或控制器需要，它就会按需创建值。 它通常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);
}
});
...
Service
Service是一个单独的JavaScript对象，包含一组用于执行某些任务的函数。 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);
}
});
Provider
AngularJS内部使用Provider在配置阶段创建服务，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，使用get（）方法返回值/ service/factory。
//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;
};
});
});
Constant
考虑到在配置阶段不能使用值这一事实，常量用于在配置阶段传递值。
mainApp.constant("configParam", "constant value");
例子 (Example)
以下示例显示了使用上述所有指令 -
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>
输出 (Output)
在Web浏览器中打开testAngularJS.htm并查看结果。
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