javascript - 为什么 ng-change 没有在 Angular JS 中触发？

Question

你能告诉我为什么 ng-change 没有在 Angular js 中触发吗？当我在日期输入字段中输入“abc”时，它仅触发一次。请告诉我如何多次开火这是我的代码

$scope.changedate =function(){
    console.log('asda')
  }

<li ng-repeat="(key, x) in c">
       <p class="input-group"  ng-if="x.date=='date'">
          <input type="text" ng-change='changedate()' class="form-control" uib-datepicker-popup="{{format}}" ng-model="x.name" is-open="x.opened" datepicker-options="dateOptions" ng-required="true" close-text="Close" alt-input-formats="formats" />
          <span class="input-group-btn">
            <button type="button" class="btn btn-default" ng-click="open1(x)"><i class="glyphicon glyphicon-calendar"></i></button>
          </span>
        </p>
      <input id='{{key}}' ng-if="x.date!='date'"  type="text" ng-model='x.name' value="{{x.name=='abc'?'ddd':'hhh'}}"/>
    </li>

http://plnkr.co/edit/neixp9ZARRAQ33gKSV9u?p=preview重现此错误的步骤

1. 运行应用程序。第一个日期字段为空。我刚刚在其中输入了1，然后 ng 更改了触发，之后我输入了 anthing 它不会触发

Answer 1

因为当您输入a时，模型值变为undefined，当您输入b时，模型值未定义，因此没有任何变化，当您输入 c 时，模型再次变为 未定义。这就是为什么不调用 ng-change 的原因。

来自 angularjs 文档:

The ngChange expression is only evaluated when a change in the input value causes a new value to be committed to the model.

It will not be evaluated:

if the value returned from the $parsers transformation pipeline has not changed if the input has continued to be invalid since the model will stay null if the model is changed programmatically and not by a change to the input value

这是我用于此类场景的辅助指令:

angular.module('viewValueChanged', [])
    .directive('viewValueChanged', viewValueChangedDirective);


function viewValueChangedDirective() {
    return {
        restrict: "A",
        require: 'ngModel',
        link: linkFn
    };

    function linkFn(scope, elem, attrs, ngModel) {
        scope.$watch(function () {
            return ngModel.$viewValue;
        }, function (newValue, oldValue) {
            if (newValue && newValue !== oldValue) {
                scope.$parent.$eval(attrs['viewValueChanged']);
            }
            // in case of user entered invalid value
            if(newValue === null) {
                scope.$parent.$eval(attrs['viewValueChanged']);
            }
        });
    }
}

并像这样使用它:

 <input uib-datepicker-popup view-value-changed="vm.onFieldsChange() />