A custom directive that enhances ngStyle by observing style changes so that if a variable in an expression changes, it can update the style as well. This is useful when binding to a resource promise in styles.

ng-custom-style.js

app.directive("myStyle", function (){
    return {
        restrict: 'A',
        link: function(scope, element, attrs)
        {
            var el   = element[0],
                attr = el.getAttribute('style');

            el.setAttribute('style', attr);

            // We need to watch for changes in the style in case required data is not yet ready when compiling
            attrs.$observe('style', function (){
                attr = el.getAttribute('style');

                if(attr)
                {
                    el.setAttribute('style', attr);
                }
            });
        }
    };
});