angularjs – 如何与指令控制器中的隔离范围变量进行交互？

我有指令myDirective,它有一个双向绑定隔离范围.当用户单击按钮时,我想将隔离范围更改为值.我认为隔离范围与$scope绑定,但我错了.我如何“抓住”并与该隔离范围进行交互？它们是否与指令控制器的范围无关？

angular.module("app",[])
.controller("myCtrl",function($scope){
    $scope.ctrlTwoway = "Eggs";
})
.directive("myDirective",function(){
    return {
        scope: {
          twoway: =
        },template: "<button ng-click="changeTwoway()">Change two way isolate scope</button>",controller: function($scope,$element,$attrs){
            $scope.changeTwoway = function(){
                // get twoway from isolate scope,and update the value with "bacon"
                // $scope.twoway = "bacon" doesn't work 
                // nor does $attrs.twoway = "bacon" work,either :(
            };
        }
    }
});

和HTML

...
<div my-directive twoway="{{ctrlTwoway}}"></div>
Current value: {{ctrlTwoway}}