AngularJS - 为什么$所适用需要妥善解决$ Q承诺？ [英] AngularJS - why is $apply required to properly resolve a $q promise?

问题描述

我试着写在我的角度应用程序的小服务，这将使我去接全球JavaScript对象指定的配置参数。我不想尝试访问全局配置对象，除非该文件已准备好（因为我不能保证在脚本元素将在HTML中插入的顺序）。

不过，我不明白为什么我需要调用 $适用的决议，实际上传播到然后回调。

  myModule.service（'GlobalConfigService'，['$ Q'，'$ rootScope'，函数（$ Q $ rootScope）{
    变种高清= $ q.defer（）;
    $（文件）。就绪（函数（）{
        def.resolve（MyConfig.val）;
        $ rootScope $适用（）。
    }）;    def.promise.then（函数（）{
        的console.log（我叫只有当$适用（）被调用，为什么呢？'）;
    }）;    返回def.promise;
}]）;
 

解决方案

在AngularJS决心的结果（）异步传播，一个$消化周期内，不会立即进行。这意味着，与随后（）注册的回调才会被调用（后）时的摘要周期发生

在您的code，没有什么是造​​成角进入消化循环，所以当时（）回调不会被调用。调用$应用（）是引起消化周期来运行的一种方法。另一种方法：添加具有NG-点击一个按钮，什么也不做，然后单击，就会造成消化周期，你应该看到的结果：

 ＆LT;按钮NG点击=＆GT;强制通过点击我＆LT消化; /按钮＆GT;
 

另请参阅 http://stackoverflow.com/a/14657974/215945

I'm trying to write a small service in my angular app which will enable me to pick config parameters specified in global Javascript objects. I don't want to attempt accessing the global config object unless the document is ready (because I cannot guarantee the order in which script elements will be inserted in the HTML).

However, I can't understand why I need the call to $apply for the resolution to actually propagate to the then callback.

myModule.service('GlobalConfigService', ['$q', '$rootScope', function($q, $rootScope) {
    var def = $q.defer();
    $(document).ready(function() {
        def.resolve(MyConfig.val);
        $rootScope.$apply();
    });

    def.promise.then(function () {
        console.log('I am called only when $apply() is called. Why?');
    });

    return def.promise;
}]);

解决方案

In AngularJS the results of resolve() are propagated asynchronously, inside a $digest cycle, not immediately. This means that callbacks registered with then() will only be called (later) when a digest cycle occurs.

In your code, nothing is causing Angular to enter a digest cycle, so the then() callback is never called. Calling $apply() is one way to cause a digest cycle to run. Another way: add a button with ng-click that does nothing, then click that, it will cause a digest cycle and you should see the results:

<button ng-click="">Force digest by clicking me</button>

See also http://stackoverflow.com/a/14657974/215945

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