$watch 与 ng-change、ng-checked 等的角度触发器变化 [英] angular trigger changes with $watch vs ng-change, ng-checked, etc

问题描述

目前我们可以通过多种方式监控数据变化.我们可以使用 $watch 触发模型更改，我们可以向元素添加指令并将一些操作绑定到它.

Currently we could monitor data changes with several ways. We could trigger model changes with $watch and we could add directives to elements and bind some actions to it.

在很多情况下有点令人困惑，所以我很好奇，每个变体的利弊，我们应该何时使用 $watch 绑定，以及何时使用像 ng 这样的指令-更改?

It's a little bit confusing in many cases, so I'm curious, which is pro and cons of each variant and when should we use $watch binding, and when directives like ng-change?

推荐答案

$watch 和 ngChange 的用法完全不同:

Both $watch and ngChange have totally different usages:

假设您在范围上定义了一个模型:

Lets say you have a model defined on a scope:

$scope.myModel = [
    {
        "foo":"bar"
    }
];

现在，如果您想在 myModel 发生任何更改时执行某些操作，您可以使用 $watch:

Now if you want to do something whenever any changes happen to myModel you would use $watch:

$scope.$watch("myModel", function(newValue, oldValue){
    // do something
});

ngChange 是一个指令，它会在用户更改输入时评估给定的表达式:

ngChange is a directive that would evaluate given expression when user changes the input:

<select ng-model="selectedOption" ng-options="option for option in options" 
ng-change="myModel=selectedOption"></select>

简而言之，您通常会将 ngChange 绑定到某个 HTML 元素.$watch 用于模型.

In short, you would normally bind ngChange to some HTML element. While $watch is for the models.

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