AngularJS指令$腕表双向绑定 [英] AngularJS directive $watch two-way binding

问题描述

我想内部变革和双向数据绑定属性的外部变化来区分（=）。

I'm trying to distinguish between internal change and an external change with a two-way data-bound attribute ('=').

在换句话说：我不想 $观看火的值，如果变化是内部（即范围变量是在控制器或改变链接功能）。

In other words: I don't want to $watch to fire on the value if the change was internal (i.e. the scope variable was changed in the controller or in the link function).

下面一些code，说明我的问题：

Here some code that illustrates my problem:

HTML

 <div ng-app="myApp">         
   <div ng-controller="MainCtrl">
     <input ng-model="value"/>
     <mydemo value="value"></mydemo>
   </div>
 </div>

的JavaScript

app.directive('mydemo', function () {
  return {
    restrict: 'E',
    scope: {
      value: "="
    },
    template: "<div id='mydiv'>Click to change value attribute</div> Value:{{value}}",

    link: function (scope, elm) 
    {      
      scope.$watch('value', function (newVal) {
      //Don't listen if the change came from changeValue function
      //Listen if the change came from input element 
      });
      // Otherwise keep any model syncing here.

      var changeValue = function()
      {
        scope.$apply(function ()
        {
          scope.value = " from changeValue function";
        });
      }

      elm.bind('click', changeValue);
    }
  }
})

现场演示：
http://jsfiddle.net/B7hT5/11/

任何想法我谁可以区分？

Any idea who can I distinguish?

推荐答案

有没有选择这两个事件之间的区别，所以你必须自己实现这一行为。

There's no option to distinguish between these two events, so you'll have to implement that behaviour yourself.

我想通过设置一个标志，每当你做出改变内部，然后在表检查它做到这一点。

I would do it by setting a flag whenever you make a change "internally", then checking for it in the watch.

例如：

link: function (scope, elm){      

  var internal = false;

  scope.$watch('value', function (newVal) {
    if(internal) return internal = false;
    // Whatever code you want to run on external change goes here.
    console.log(newVal);
  });

  var changeValue = function(){
    scope.$apply(function (){
      internal = true; // flag internal changes
      scope.value = " from changeValue function";                              
    });
  }

  elm.bind('click', changeValue);
}

查看更新拨弄。

您的替代（更复杂）的方法，是创建一个使用 ngModel API自定义指令。 >模型（外部）和型号 - - > DOM（内部）的变化DOM之间的区分。我不认为有必要在这里，虽然。

Your alternative (more complex) approach, is creating a custom directive that uses the ngModel API. That distinguishes between DOM -> Model (external) and Model -> DOM (internal) changes. I don't think it's necessary here, though.

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