问题描述
我有一个问题：什么时候应该使用角 $观看功能，当使用 NG-变化 angularjs指令？对我来说，它们都可以这样做。
I have a question: When should I use angular $watch functions and when use ng-change angularjs directive? To me, they both can do the same.
它们之间有任何分歧或使用模式？
Are there any differences or usage patterns between them?
推荐答案
他们是不一样的，清晰。一个是在所述控制器单独使用;另一种是一个输入元件上的指令。
They are not the same, clearly. One is used solely in the controller; the other is a directive on an input element.
但是，即使在应用它们之间的区别。
But even in their application they differ.
当您使用 $腕表的看着前pression将在每一个消化周期评估，如果有变化，处理程序被调用。
When you use $watch the watched expression will be evaluated on every digest cycle, and if there is a change, the handler is invoked.
使用 NG-变化，处理程序以响应事件显式调用。
With ng-change, the handler is invoked explicitly in response to an event.
使用 $观看，变化可以来自任何地方：用户操作，控制器的功能，服务 - 都将触发处理程序
With $watch, change can come from anywhere: user action, controller function, service - all will trigger the handler.
使用 NG-变化，变化仅限于一个特定的输入元件上的用户操作。
With ng-change, the change is restricted to a user action on a particular input element.
值得也需要注意的是 NG-变化作品仅的结合 NG-模型 - 换句话说，在 NG-变化前pression进行评估，只有当 ngModel $ viewValue （参见<$c$c>ngModelController对于更多的信息文档）被改变，其通常发生在响应于用户启动的事件。
It is worth to note also that ng-change works only in combination with ng-model - in other words, the ng-change expression is evaluated only when ngModel.$viewValue (refer to ngModelController documentation for more info) is changed, which typically happens in response to a user-initiated event.
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