MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

Network Information and Connectivity
In the previous chapter, I mentioned in a footnote how at the very time I was writing on the subject of
live tiles and all the connections that Windows 8 apps can have to the Internet, my home and many
thousands of others in Northern California were completely disconnected due to a fiber optic
breakdown. The outage lasted for what seemed like an eternity by present standards—36 hours!
Although I wasn’t personally at a loss for how to keep myself busy, there was a time when I opened one
of my laptops, found that our service was still down, and wondered for a moment just what the
computer was really good for without connectivity! Clearly I’ve grown, as I suspect you have too, to take
constant connectivity completely for granted.
As developers of great apps, however, we cannot afford to be so complacent. It’s always important to
handle errors when trying to make connections and draw from online resources, because any number of
problems can arise within the span of a single operation. But it goes much deeper than that. It’s our job
to make our apps as useful as they can be when connectivity is lost, perhaps just because our customers
got on an airplane and switched on airplane mode. That is, don’t give customers a reason to wonder
about the usefulness of their device in such situations! A great app will prove its worth through a great
user experience even if it lacks connectivity.
Connectivity can also vary throughout an app session, where an app can often be suspended and
resumed, or suspended for a long time. With mobile devices especially, one might switch between any
number of networks without necessarily knowing about it. Windows 8, in fact, tries to make the
transition between networks as transparent as possible, except where it’s important to inform the user
that there may be costs associated with the current network. It’s required by Window Store policy, in
fact, for apps to be aware of data transfer costs on metered networks and to prevent “bill shock” from
not-always-generous mobile broadband providers. Just as there are certain things an app can’t always
do when the device is offline, the characteristics of the current network might also cause it to defer or
avoid certain operations as well.
Let’s now see how to retrieve and work with connectivity details, starting with the different types of
networks represented in the manifest, followed by obtaining network information, dealing with metered
networks, and providing for an offline experience.
Network Types in the Manifest
Nearly every sample we’ve worked with so far in this book has had the Internet (Client) capability
declared in its manifest, thanks to Visual Studio turning that on by default. Once before I mentioned
how this wasn’t always the case: early app builders within Microsoft would occasionally scratch their
heads wondering just why something really obvious—like making a simple XmlHttpRequest to a
blog—failed outright. Without this capability, there just isn’t any Internet!
Still, Internet (Client) isn’t the only player in the capabilities game. Some networking apps will also
want to act as a server to receive incoming traffic from the Internet, and not just make requests to other
631