何时在 Angularjs 中使用 $watch 或 ng-change [英] When to use $watch or ng-change in Angularjs

问题描述

我什么时候应该使用 angular $watch 函数，什么时候使用 ng-change angularjs 指令?对我来说，他们都可以做同样的事情.

When should I use angular $watch functions and when use ng-change angularjs directive? To me, they both can do the same.

它们之间有什么区别或使用模式吗?

Are there any differences or usage patterns between them?

推荐答案

很明显，它们不一样.一个单独用于控制器；另一个是输入元素上的指令.

They are not the same, clearly. One is used solely in the controller; the other is a directive on an input element.

但即使在他们的应用中它们也不同.

But even in their application they differ.

当您使用 $watch 时，监视的表达式将在每个摘要周期上进行评估，如果有更改，则调用处理程序.

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-change，处理程序被显式调用以响应事件.

With ng-change, the handler is invoked explicitly in response to an event.

使用 $watch，更改可以来自任何地方:用户操作、控制器功能、服务 - 所有这些都会触发处理程序.

With $watch, change can come from anywhere: user action, controller function, service - all will trigger the handler.

使用 ng-change，更改仅限于用户对特定输入元素的操作.

With ng-change, the change is restricted to a user action on a particular input element.

还值得注意的是，ng-change仅与 ng-model 结合使用 - 换句话说，ng-change 表达式仅在 ngModel.$viewValue 时被评估(参考 ngModelController 文档以获取更多信息)已更改，这通常是为了响应用户发起的事件而发生的.

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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