AngularJS：观察对象数组中的特定属性,以获取属性值的更改

在我的自定义指令中,我根据数据源数组中的对象数量向DOM添加元素.我需要在每个对象中观察特定属性.当我将这些元素添加到DOM时,我想在toppings数组中的每个对象的checked属性上设置$watch,但它不起作用,我不知道为什么.我在函数内部设置了一个断点,当属性从true变为false或false变为true时应该调用该断点,但永远不会调用该函数.原因很明显吗？我只是在学习Angular,所以我很容易犯一个愚蠢的错误.

$scope.bits = 66;  (i.e. onions and olives)


$scope.toppings = [
    { topping: 1,bits: 2,name: 'onions' },{ topping: 2,bits: 4,name: 'mushrooms' },{ topping: 3,bits: 8,name: 'peppers' },{ topping: 4,bits: 16,name: 'anchovies' },{ topping: 5,bits: 32,name: 'artichokes' },{ topping: 6,bits: 64,name: 'olives' },{ topping: 7,bits: 128,name: 'sausage' },{ topping: 8,bits: 256,name: 'pepperoni' }
     ]

模型中的每个对象都会获得一个新的checked属性,该属性为true或false.

注意：对象数组最多包含十几个项目.性能不是问题.

link: function link(scope,iElement,iAttrs,controller,transcludeFn) {


  <snip>

 // At this point  scope.model refers to $scope.toppings. Confirmed.

  angular.forEach(scope.model,function (value,key) {

     // bitwise: set checked to true|false based on scope.bits and topping.bits

     scope.model[key].checked = ((value.bits & scope.bits) > 0);  


     scope.$watch(scope.model[key].checked,function () {
         var totlBits = 0;
         for (var i = 0; i < scope.model.length; i++) {
            if (scope.model[i].checked) totlBits += scope.model[i].bits;
         }
          scope.bits = totlBits;
      });

   });

     <snip>