Saturday, August 04, 2012

Spare your users the high cost of data roaming

You may have heard reports from the media, regarding the high cost of roaming charges that some people incurred. It's really no surprise, as some network carriers are practicing predatory pricing every time you leave the borders of their home country.

Although the end users are ultimately responsible for those charges, we, as developers, should strive to warn them when they're about to do some data transfers while using the apps we developed, if they're likely to be roaming at the time.  That would help people that haven't turned off data roaming, through the settings provided by iOS.

The problem is that AFAIK there's no API exposed by iOS to determine if the user is roaming. So we'll need to get creative. First off, we have the SystemConfiguration.framework, which allows us to determine whether a Wi-Fi or cellular connection is in use. If it's the former, we have a non-issue. There won't be any roaming charges for Wi-Fi connections. If it's the latter we need to dig deeper. We could use the CoreLocation.framework to determine the current location of the device.

Then we could use NSLocale and its ability to determine the county code of the current locale (likely established when the device is first set up).

If the country of the locale differs from the country of the current location, there's a high probability that the user is roaming, so we could warn them about potential charges before any data transfer is initiated by the app.

This heuristic is not fool-proof, but it's better than nothing, and it can go a long way towards preventing some unwanted charges. An alternative is to track changes in the country reported by the core location framework and use that as a hint of possible roaming. A possible complication may be caused by the user not authorizing the app for location lookups. There's a way around that, which I'll explore in a future blog post.

The best approach would be to have an API to tell precisely when a user is roaming, and better yet, the data rates for that particular destination, but that will be the topic for another blog post.

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