Angularjs directive: Icheck doesn't capture the first switch from true to false

问题

Hi' I'm using Icheck with angularjs and I have a problem with the first switch from true to false, the $watch on ngModel isn't called and so it keeps value true in my angular variable. Where is the error? This is the code

app.directive('icheck2', function ($timeout, $parse) {
    return {
        require: 'ngModel',
        link: function ($scope, element, $attrs, ngModel) {
            return $timeout(function () {
                $scope.$watch($attrs['ngModel'], function (newValue) {
                    $(element).iCheck('update');
                }); 

                    //Initialize first checkbox
                    if ($(element)[0].value == "true")
                        $(element).iCheck('check');
                    else
                        $(element).iCheck('update');//even uncheck doesn't work


                return $(element).iCheck({
                    checkboxClass: 'icheckbox_square-blue',
                    radioClass: 'iradio_square-blue'
                }).on('ifChanged', function (event) {
                    if ($(element).attr('type') === 'checkbox' && $attrs['ngModel']) {
                        $scope.$apply(function () {
                            return ngModel.$setViewValue(event.target.checked);
                        })
                    }
                });
            });
        }
    };
});

On HTML I have:

<div data-ng-repeat="accessory in reservation.accessories"
    style="margin-Top: 10px;"
    data-ng-if="accessory.idType == accessoryType.CHECKBOX_TYPE">
    <input icheck2 type="checkbox" name="iCheck2" data-ng-model="accessory.value"
        value="{{accessory.value}}" id="checkbox{{accessory.id}}">
    <span style="margin-left: 5px;">{{accessory.name}}</span>
</div>

UPDATE: I have the same problem with bootstrap switch:

app.directive('bootstrapSwitch', 
        [
         function() {
             return {
                 restrict: 'A',
                 require: '?ngModel',
                 link: function(scope, element, attrs, ngModel) {
                     element.bootstrapSwitch({size: "small", onColor:"success", offColor:"danger"});
                     // ngModel.$setViewValue(false); //set start status to false

                     element.on('switchChange.bootstrapSwitch', function(event, state) {
                         if (ngModel) {
                             scope.$apply(function() {
                                 ngModel.$setViewValue(state);
                             });
                         }
                     });

                     scope.$watch(attrs.ngModel, function(newValue, oldValue) {
                         if (newValue) {
                             element.bootstrapSwitch('state', true, true);
                         } else {
                             element.bootstrapSwitch('state', false, true);
                         }
                     });
                 }
             };
         }
         ]
);

来源：https://stackoverflow.com/questions/47092037/angularjs-directive-icheck-doesnt-capture-the-first-switch-from-true-to-false