I am working on a social-networking-type app where the user sees a list of "posts" and can interact with them, notably they can "like" them.
The list of posts is in the 10,000s and so we paginate it using Android's paging library (DB + Network), but this is applicable to any situation where there are cached objects that need to be modified.
Loading and paginating the list is working great, very responsive and the built-in animations are nice. The problem is when the user likes a post. In order to like a post, there is a button on the list item. When the user likes (or "unlikes") the post, the button's icon changes and "like count" increments or decrements accordingly and we have to make a call to the appropiate web service. It's all basic social networking stuff and seems pretty simple, but I am struggling with how to update the data correctly and efficiently. So far I've come up with three possibilities but they all suck:
- make the request and receive the updated object, then reinsert it into the database. This is easy and ensures that the data is correct but it means that the user has to wait for the request to return before the UI is refreshed, which usually results in the user clicking multiple times on the image (performing multiple requests). So pretty much useless.
- modify the UI (the list item view updates it's visual state) but not the backing data, then make the request and insert the result back into the DB. This is a huge PITA as it results in a visual state that is not in sync so if the user scrolls around and comes back before the request completes they will see the original state. I also have to communicate errors back to the view so it can revert its state.
- modify the object in memory (change the like count and user-post-like relation), making a copy of the original, reinsert it into the database, make the request, then insert the updated object from the web service or the original object in case of error. This gives instant visual feedback and preserves data integrity but is only mildly less of a PITA.
So for the moment I'm going with 3 because it seems to be the best but I am wondering if there is a better way to handle this? It seems like I'm banging my head on such a basic functionality, surely this problem has been solved a million times before? I am not used to working with caching on CRUD systems (I have implemented basic caching for read-only data) but modifying the cache is turning out to be a bigger obstacle than I expected.
