Design for annotating UICollectionView selections with additional controls

Question

Using UICollectionView and excellent help given on here on StackOverflow, I've been able to build a "Gantt Chart" style control for my iPhone:

Cosmetics aside (I'm doing the functional right now, I've got a graphics designer on tap to look at colors and all that).

Background aside, the spans were relatively straightforward to do with a custom UICollectionViewLayout subclass. Each span is an item.

But I need to add some functionality, and am unsure how to proceed. Where I'm trying to go is illustrated roughly as:

Sketchy cosmetics aside, the point is that I want to "annotate" whatever the currently selected span is with additional information (I promise to find someone to help me look it pretty). And I want them to be active, I'm not sure if it brings up an editing control or does drag, but I want to be able recognize gestures on either the numbers or the bold lines and do things with them, distinct from touching on the span which drives selection.

I can think of (at least) 3 ways to try and implement this:

1. Use supplementary views. Cause selection to invalidateLayout, detect the selected state in my prepareLayout, and generate additional layout attributes for the two anchors. Implement a subclass of UICollectionReusableView which does the drawing, and adds touchable subviews (or its own gesture recognizers). This feels... wrong. I get the idea that supplementary views are more for headers and footers, not for controls that come and go as the selection state changes. But maybe it's an appropriate extension of the facility?

2. Use the backgroundView (or selectedBackgroundView, not sure it matters) of my current SpanCell class (which is a subclass of UICollectionViewCell). As long as I disable clipsToBounds, I can draw the annotation around the bounds of the span. I'll have to give it some knowledge of the big picture to find the endpoints, but that's not too offensive. I would just show/hide this view in response to selection changes. This seems like the best way to do it.

3. Do it in the main backgroundView of the entire UICollectionView. As shown, I've already got a specialized backgroundView which shows the the current time grid, strip style. I could further extend this view to draw annotations and manage touchable sub controls in response to selection changes. This would give me most direct implementation, but it feels like I'll end up with a big monster "doing too many jobs" object for the background.

Question then, for those who have more experience, is which route would you go? Would it be one of the above 3? Or something different? And why?

Answer 1

While your question is very technical with UICollectionView implementation, which I am not very familiar with, this seems like a job for the container (in this case, the collection view). Imagine you need your annotation to consider, in addition to the selected item, other items? Like for example, avoiding collision between annotation lines and another item?

For me, option number 3 seems like the most correct one. If you fear a large class, you can extern it to an annotation controller class, which should be notified whenever the annotations should be updated.