angularjs - waiting for a value to be bound to a directive - angularjs

Question

I am experiencing a strange situation with angularjs. I have a value bound to a directive, and I need to be able to check on and manipulate that value from both the controller and a directive. I also have a method as a property of an object bound to the directive that I need to call from the controller. The method is expected to react accordingly to the bound value.
Here is some pseudo code to illustrate it:
.controller('ctrl', function(){
$scope.someAction = function(){
$scope.myValue = undefined;
$scope.someObject.myMethod();
};
});
.directive('myDirective', ...){
return {
...
scope: { myValue: '=', someObject: '=' },
link: function (scope) {
scope.someObject = {
myMethod: function(){
if (angular.isDefined(scope.myValue)){
// do something
}
else {
// do something else
}
}
};
}
}
}
and in controller template:
<my-directive my-value="myValue" some-object="someObject"></my-directive>
I would expect that when "someAction" is triggered, "myValue" set to undefined and the method "someObject.myMethod" is called from the controller, "myValue" in the directive is undefined, but it isn't that way. However, if I wrap the method call in a $timeout that waits for just 1 millisecond, I get the expected behaviour:
.controller('ctrl', function($timeout){
$scope.someAction = function(){
$scope.myValue = undefined;
$timeout(function() {
$scope.someObject.myMethod();
}, 1);
};
});
This hack has solved my problem, but I would prefer to understand what is going on and perhaps solve it (or avoid it) more elegantly...

Answer 1

Your controller's function $scope.someAction is wrapped by angular into an $apply call. So, probably, when you call $scope.someObject.myMethod(), the directive's isolated scope isn't updated because $apply didn't end. A solution would be to do something like you suggested:
$timeout(function() {
$scope.someObject.myMethod();
}, 0);
The timeout will delay to the execution of function to the next $apply call so your directive will see the updated value.