Javascript 在我的自定义指令中未定义控制器模型

我在angular应用程序中添加了一个自定义指令，该指令负责验证邮件是否有效，该指令似乎运行良好，因为我收到了错误消息：

myApp.directive('validateEmail', function(ValidationService) {
    return {
      require: 'ngModel',
      controller: function($element) {
        var ctrl = $element.controller('ngModel');

        ctrl.$validators.validateEmail =
          function(modelValue, viewValue) {
            return ValidationService.isValidEmail(viewValue);
        };
      }
    };
});

当我试图提交表格时，在控制台中出现了以下奇怪的错误：

错误：ctrl未定义 控制器@ 援引@ $ControllerProvider/this$gethttps://code.angularjs.org/1.5.1/angular.js:9886:24 nodeLinkFn@ 复合物@ 公共链接fn@

---

CompliationGenerator/将控制器更改为链接

myApp.directive('validateEmail', function(ValidationService) {
    return {
      require: 'ngModel',
      link: function (scope, element, attrs, ctrl) {
        ctrl.$validators.validateEmail =
          function(modelValue, viewValue) {
            return ValidationService.isValidEmail(viewValue);
        };
      }
    };
});

---

将控制器更改为链接

myApp.directive('validateEmail', function(ValidationService) {
    return {
      require: 'ngModel',
      link: function (scope, element, attrs, ctrl) {
        ctrl.$validators.validateEmail =
          function(modelValue, viewValue) {
            return ValidationService.isValidEmail(viewValue);
        };
      }
    };
});