MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

Tap to Connect and Tap to Activate
To detect a direct NFC tap—which again works to connect apps running on two devices—listen to the
PeerFinder.ontriggeredConnectionStateChanged (a WinRT event that I spell out in camel casing so
that it’s readable!). In response, start the PeerFinder:
ProxNS.PeerFinder.ontriggeredconnectionstatechanged = triggeredConnectionStateChangedEventHandler;
ProxNS.PeerFinder.start();
The process of connecting through tapping will go through a series of state changes (including user
consent), where those states are described in the TriggeredConnectState enumeration: listening,
connecting, peerFound, completed, canceled, and failed. Each state is included in the event args sent to
the event (a TriggeredConnectionStateChangedEventArgs…some of these names sure get long!), and
when that state reaches completed, the socket property in the event args will contain the StreamSocket
for the connection:
function triggeredConnectionStateChangedEventHandler(e) {
// [Other cases omitted]
}
if (e.state === ProxNS.TriggeredConnectState.completed) {
startSendReceive(e.socket);
}
Again, from this point on, it’s a matter of what data is being exchanged through the socket—the NFC
tap is just a means to create the connection. And once again, call the socket’s close when you’re done
with it.
When tapping connects the same app across devices, it’s possible to have the tap launch an app on
one of those devices. That is, when the app is running on one of the devices and has started the
PeerFinder, Windows will know the app’s identity and can look for it on the other device. If it finds that
app, it will launch it (or activate it if it’s already running). The app’s activated handler is then called with
an activation kind of launch, where eventArgs.detail.arguments will contain the string
“Windows.Networking.Proximity.PeerFinder:StreamSocket” (see js/default.js):
var tapLaunch = ((eventObject.detail.kind ===
Windows.ApplicationModel.Activation.ActivationKind.launch) &&
(eventObject.detail.arguments ===
"Windows.Networking.Proximity.PeerFinder:StreamSocket"));
if (tapLaunch) {
url = scenarios[0].url; // Force scenario 0 if launched by tap to start the PeerFinder.
}
return WinJS.Navigation.navigate(url, tapLaunch);
The code in Scenario 1 picks up this condition (the tapLaunch parameter to WinJS.-
Navigation.Navigate is true) and calls PeerFinder.start automatically instead of waiting for a button
press. In the process of startup, the app also registers its own triggeredConnection-StateChanged
handler so that it will also receive a socket when the connection is complete.
705