The Short Story
The short story is that PointsStalker can now update the Athletes and Points database on its own. PointsStalker checks for new databases at startup and will download the updated data in the background. The data associated with Groups will be kept, so updates should be unnoticeable aside from new data being presented when viewing an athlete.
The Long Story
Building the API server was a longer path of discovery than I expected. This was my first time building any kind of web service and I learned a lot.
The API Basics
I decided to build the API on Sinatra. I liked Sinatra because it felt straight forward, all the routes are defined in one file, but still offers a lot of flexibility because it is built on top of Rack. Everything in one file; sounds simple right? Well, it is, but considering this was my first project in Ruby I had some catching up to do.
I felt it went well though, I did a few Ruby, Sinatra and Ruby on Rails tutorials and I jumped in. The basics came pretty easily, but, as with everything, the devil is in the details (gem file conflicts, configuring middleware, deploying to Heroku, etc.).
How the API Works
Since it's my first time writing both iOS apps and server APIs I wanted to keep each component as basic and modular as possible. In particular, I figured I could always add functionality or complexity in the future, but I wanted to avoid getting stuck trying to do too much (or as my Dad used to say, 'come in hot and run out of talent'). So, the API is designed to deliver a JSON hash of the most recent database information the API is aware of for that version of the iOS app. Such data includes the list ID number, the date the list is valid, the date the list is valid to and, most importantly, a download link for this most recent database.
Upon receiving the latest database information for the API the iOS app will compare the JSON information to the information currently held on the phone and if the database held by the API is more recent then the iOS app will download the new SQLite database to replace the out of date information.
Connecting to the API
When I started working on PointsStalker I had plans for how to approach every component of the app — including backup plans incase I got in over my head — every component except for one, networking. I knew almost nothing about networking from a programming perspective, yet it was critical to PointsStalker's overall functionality. So, in the process of reading the thousands of StackOverflow posts and listening to hundreds of developer podcasts while developing PointsStalker I always kept networking in the back of my mind. And at some point along the way I heard Marco Arment talking about using AFNetworking, so I kept it in mind for later.
As it turns out, I probably shouldn't have been so concerned about networking. The internet is part of the foundation of nearly every single app created today, thus the tools must to be well developed and easily understood. It was incredibly simple to set up AFNetworking, make my HTTP GET requests and parse the JSON responses. It was even easier to download a link to a file in my S3 bucket, but my bubble had to burst at some point.
Configuring Background Fetch and Background Downloads
I fell back to earth while trying to configure the iOS background fetch API. The fetch API wasn't an issue, just figure out how to use the completion handler and implement application:performFetchWithCompletionHandler: in the app delegate. The problem became handling background downloads.
Again, the iOS API for handling background NSURLSessions was easy enough to understand. My difficulties stemmed from how to configure AFNetworking to use a NSURLSessionConfiguration for background downloading (which seemed more difficult than I felt it would to be). Eventually I got it figured out, but either I missed something or AFNetworking doesn't have a convenient way to configure download request for background downloading using the standard download methods. If you're in search of a solution check out this StackOverflow answer.
With the API server up and running and the app successfully functioning with background API fetching and background downloads I feel good. There are still some bugs I need to try to iron out, but I'd feel pretty good about shipping what I have today.
- DOB 1 day off for some people
- Database status string doesn't update
- Points graph legend gets compressed when using 'cursor'