详解angularjs利用ui-route异步加载组件

ui-route相比于angularjs的原生视图路由更好地支持了路由嵌套，状态转移等等。随着视图不断增加，打包的js体积也会越来越大，比如我在应用里面用到了wangeditor里面单独依赖的jquery就300多k。异步加载各个组件就很有必要。在这里我就以ui-route为框架来进行异步加载说明。

首先看一下路由加载文件

angular.module('webtrn-sns').config(['$stateProvider', function ($stateProvider) {
  $stateProvider.state({
      name: 'home.message',
      url: '/message',
      abstract: true,
      templateProvider: ['resources', function (resources) {
        return resources.template
      }],
      controllerProvider: ['resources', (resources)=> {
        return resources.controller
      }],
      onEnter: ['resources', (resources)=>resources.css.use()],
      onExit: ['resources', (resources)=>resources.css.unuse()],
      resolve: {
        resources: ()=> {
          return new Promise(
            resolve => {
              require([], () => {
                resolve({
                  css: require('./css/message_box.css'),
                  template: require('./html/message_box.html'),
                  controller: require('./js/message_box.js')
                })
              })
            }
          );
        }
      }
    }
  ).state({
      name: 'home.message.add_message',
      url: '/add_message?isReply&toUid&title',
      params: {isReply: null, toUid: null, title: null},
      templateProvider: ['resources', function (resources) {
        return resources.template
      }],
      controllerProvider: ['resources', (resources)=> {
        return resources.controller
      }],
      onEnter: ['resources', (resources)=>resources.css.use()],
      onExit: ['resources', (resources)=>resources.css.unuse()],
      resolve: {
        resources: ()=> {
          return new Promise(
            resolve => {
              require(['./js/message.js'], () => {
                resolve({
                  css: require('./css/add_message.css'),
                  template: require('./html/add_message.html'),
                  controller: require('./js/add_message.js')
                })
              })
            }
          );
        }
      }
    }
  )
}])

这个是路由状态的一个声明文件，name,url,param字段的方式不变，关键是看resolve这个部分。根据ui-route的resolve文档,resolve是为了给state或者controller进行自定义注入对象的。

下面是举出文档中关于resolve的例子：

$stateProvider.state('myState', {
   resolve:{
     // Example using function with simple return value.
     // Since it's not a promise, it resolves immediately.
     simpleObj: function(){
      return {value: 'simple!'};
     },
     // Example using function with returned promise.
     // This is the typical use case of resolve.
     // You need to inject any services that you are
     // using, e.g. $http in this example
     promiseObj: function($http){
      // $http returns a promise for the url data
      return $http({method: 'GET', url: '/someUrl'});
     },
     // Another promise example. If you need to do some
     // processing of the result, use .then, and your
     // promise is chained in for free. This is another
     // typical use case of resolve.
     promiseObj2: function($http){
      return $http({method: 'GET', url: '/someUrl'})
        .then (function (data) {
          return doSomeStuffFirst(data);
        });
     },
     // Example using a service by name as string.
     // This would look for a 'translations' service
     // within the module and return it.
     // Note: The service could return a promise and
     // it would work just like the example above
     translations: "translations",
     // Example showing injection of service into
     // resolve function. Service then returns a
     // promise. Tip: Inject $stateParams to get
     // access to url parameters.
     translations2: function(translations, $stateParams){
       // Assume that getLang is a service method
       // that uses $http to fetch some translations.
       // Also assume our url was "/:lang/home".
       return translations.getLang($stateParams.lang);
     },
     // Example showing returning of custom made promise
     greeting: function($q, $timeout){
       var deferred = $q.defer();
       $timeout(function() {
         deferred.resolve('Hello!');
       }, 1000);
       return deferred.promise;
     }
   },
   // The controller waits for every one of the above items to be
   // completely resolved before instantiation. For example, the
   // controller will not instantiate until promiseObj's promise has
   // been resolved. Then those objects are injected into the controller
   // and available for use.
   controller: function($scope, simpleObj, promiseObj, promiseObj2, translations, translations2, greeting){
     $scope.simple = simpleObj.value;
     // You can be sure that promiseObj is ready to use!
     $scope.items = promiseObj.data.items;
     $scope.items = promiseObj2.items;
     $scope.title = translations.getLang("english").title;
     $scope.title = translations2.title;
     $scope.greeting = greeting;
   }
  })

我们可以看到resolve的对象是支持Promise的。

再回到我们之前的代码templateProvider和controllerProvider我们注入了resources的模板对象和controller对象，onEnter和onExit注入了css模块。

如果controller中依赖了服务怎么办的？

resolve: {
  resources: ()=> {
    return new Promise(
      resolve => {
        require(['./js/message.js'], () => {
          resolve({
            css: require('./css/add_message.css'),
            template: require('./html/add_message.html'),
            controller: require('./js/add_message.js')
          })
        })
      }
    );
  }
}

可以在require里面将服务注入，如代码中的message.js。而为了将服务进行异步加载我们不能用普通的.factory或者.service。而需要调用$provide.factory或者$provide.service

如果采用webpack进行编译打包的话就需要webpack.optimize.CommonsChunkPlugin的支持，这样可以对js进行拆分打包，达到异步加载js的目的。

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