AngularJS : $watch within directive is not working when $rootScope value is changed

问题

I have created an application is angularjs in which i am having a directive, i am ahving a watch within the directive to trigger some methods within the directive when there is a change in $rootScope variable, but the problem is when the $rootScope.name value is changed the watch which is within the directive is not working

My code is as given below

Working Demo

var module = angular.module('myapp', []);

module.controller("TreeCtrl", function($scope, $rootScope) {
    $scope.treeFamily = {
        name : "Parent"
    };

    $scope.changeValue = function()
    {
        $rootScope.name = $scope.userName;
    };

});

module.directive("tree", function($compile) {
    return {
        restrict: "E",
        transclude: true,
        scope: {},
        template:'<div>sample</div>',
        link : function(scope, elm, $attrs) {
           function update()
           {
           };
           scope.$watch('name', function(newVal, oldVal) {
                console.log('calling');
               update();
            }, true);
        }
    };
});

回答1:

i have corrected it. for working fiddle

<div ng-app="myapp">
  <div ng-controller="TreeCtrl">
    <input type="text" ng-model="userName"/>
    <button ng-click="changeValue()">Change</button>
    <tree name="name">
    </tree>
  </div>
</div>



module.directive("tree", function($compile) {
  return {
    restrict: "E",
    transclude: true,
    scope: {
        name: '='
    },
    template:'<div>sample</div>',
    link : function(scope, elm, $attrs) {
       function update()
       {
       };
       scope.$watch('name', function(newVal, oldVal) {
            console.log('calling');
           update();
        }, true);  
    }
  };
});

回答2:

scope: {},

You use an isolated scope. It doesn't inherit from a parent scope, so name doesn't exist in this scope. Since you define it directly in $rootScope you could access it in your directive:

module.directive("tree", function($compile, $rootScope) {
    ...
    link : function(scope, elm, $attrs) {
       function update()
       {
       };
       $rootScope.$watch('name', function(newVal, oldVal) {

Using the root scope is not the best idea though. I wouldn't put name into the root scope to begin with. Better put it into the controller's scope and use binding, similar to the solution proposed by @simon.

来源：https://stackoverflow.com/questions/27265695/angularjs-watch-within-directive-is-not-working-when-rootscope-value-is-chan