Sample code for iOS and Android, to post to the web, and get a response back.
Lots of apps need to be able to retrieve data from the web, so this is a simple example to do it.
There's a simple PHP script running on the CS department web server that expects a number to come in from a "post" HTTP request. It then doubles that number, and returns the result as JSON. The apps take a number typed into a text box on screen, send that to the web server (using a couple of simplified wrappers around the standard HTTP tools), and then put the result on screen when the web server response.
There are a couple of "gotchas" to be careful of -- mostly revolving around the asynchronous nature of web interactions. The iOS version of the code has a "completion block" that gets called when the response from the web server comes in. THIS IS ON A THREAD THAT CANNOT ACCESS THE USER INTERFACE! Note that in the ViewController, there is "performSelectorOnMainThread", which is called from the completion block. This puts a request to call the function into a queue, and then when a thread that has access to the user interface runs, the function is called.
There's a "networker" class in the iOS code that you can grab and use; it makes the interactions with the HTTP classes a little easier (in my opinion!). Values are set to the web server by creating an NSDictionary -- essentially a key/value array. What comes back is JSON, and we can extract the result from that.
For Android, the structure is similar, and there are the same sort of thread-constraints. In the Java code, there's a "NetTask" class, which is an extension of the AsyncTask base class. It can run in the background, and handles the required waiting to get a result back from the web server. The data coming back from the web server has to be read (in a loop), and built up; that's what "readAll" does. Once the data is back, we call the "netResult" method on the MainActivity class, which updates the screen -- note that this is done by calling "runOnUiThread".
The Networker class in the iOS version, and the NetTask class for Android, are code that I cobbled together from a variety of sources, trying to make something that was a little bit cleaner, and a little bit more consistent. This is by no means the "only way to do it" -- just the way I knocked it together here. There are a lot of packages that will wrap the HTTP interface; trying to keep it relatively clean, simple, and comprehensible.
Once you can upload and download numbers.... pretty much anything is do-able!