_affixWithinContainer.md

What this does:

Within an <ion-scroll>, this directive creates sticky item headers that get bumped out of the way by the next item.

Demo: http://cl.ly/2u2X390s0H1a

Requirements:

• Needs UnderscoreJS for its _.throttle utility.
• Must be used within an <ion-scroll> or <ion-content>
• You must group each header and contents together within a container element (this container element defines the area in which the header should stay).
• Not tested with collection-repeat -- only with ng-repeat (please let me know if it works and I'll update)
• This directive works by cloning the "sticky header" and appending it between the outer scroll container and inner scroll container -- as a sibling of the scrollbar, for reference. Thus, you might need to edit your CSS if it doesn't already apply correctly to the cloned header element.

Example: If you want to render a list of posts with sticky post titles, you could create markup like this:

<article class="post" ng-repeat="post in posts track by post.id">
    <h1>Post Title</h1>
    <main>
        <p>Long post body with many paragraphs...</p>
    </main>
</article>

Then all we need to do is make sure it's within an <ion-scroll>, and add the affix-within-container=".post" attribute to the <article>. (See affixWithinContainer.html below)

Where affix-within-container=".post" tells the <h1> that it is the sticky header for everything within it's closest .post ancestor. i.e. $(element).closest('.post').

affixWithinContainer.html

<ion-content scroll-event-interval="5"><!-- or <ion-scroll> -->
    <article class="post" ng-repeat="post in posts track by post._id">
        <h1 affix-within-container=".post">
            {{post.title}}
        </h1>
        <main>
            {{post.body}}
        </main>
    </article>
</ion-content>

affixWithinContainer.js

.directive('affixWithinContainer', function($document, $ionicScrollDelegate) {

  var transition = function(element, dy, executeImmediately) {
    element.style[ionic.CSS.TRANSFORM] == 'translate3d(0, -' + dy + 'px, 0)' ||
    executeImmediately ?
    element.style[ionic.CSS.TRANSFORM] = 'translate3d(0, -' + dy + 'px, 0)' :
    ionic.requestAnimationFrame(function() {
      element.style[ionic.CSS.TRANSFORM] = 'translate3d(0, -' + dy + 'px, 0)';
    });
  };

  return {
    restrict: 'A',
    require: '^$ionicScroll',
    link: function($scope, $element, $attr, $ionicScroll) {
      var $affixContainer = $element.closest($attr.affixWithinContainer) || $element.parent();

      var top = 0;
      var height = 0;
      var scrollMin = 0;
      var scrollMax = 0;
      var scrollTransition = 0;
      var affixedHeight = 0;
      var updateScrollLimits = _.throttle(function(scrollTop) {
          top = $affixContainer.offset().top;
          height = $affixContainer.outerHeight(false);
          affixedHeight = $element.outerHeight(false);
          scrollMin = scrollTop + top;
          scrollMax = scrollMin + height;
          scrollTransition = scrollMax - affixedHeight;
      }, 500, {
          trailing: false
      });

      var affix = null;
      var unaffix = null;
      var $affixedClone = null;
      var setupAffix = function() {
          unaffix = null;
          affix = function() {
              $affixedClone = $element.clone().css({
                  position: 'fixed',
                  top: 0,
                  left: 0,
                  right: 0
              });
              $($ionicScroll.element).append($affixedClone);

              setupUnaffix();
          };
      };
      var cleanupAffix = function() {
          $affixedClone && $affixedClone.remove();
          $affixedClone = null;
      };
      var setupUnaffix = function() {
          affix = null;
          unaffix = function() {
              cleanupAffix();
              setupAffix();
          };
      };
      $scope.$on('$destroy', cleanupAffix);
      setupAffix();

      var affixedJustNow;
      var scrollTop;
      $($ionicScroll.element).on('scroll', function(event) {
        scrollTop = (event.detail || event.originalEvent && event.originalEvent.detail).scrollTop;
        updateScrollLimits(scrollTop);
        if (scrollTop >= scrollMin && scrollTop <= scrollMax) {
            affixedJustNow = affix ? affix() || true : false;
            if (scrollTop > scrollTransition) {
                transition($affixedClone[0], Math.floor(scrollTop-scrollTransition), affixedJustNow);
            } else {
                transition($affixedClone[0], 0, affixedJustNow);
            }
        } else {
            unaffix && unaffix();
        }
      });
    }
  }
});