Windows 8 Platform NFC Development Guide

Windows 8 Platform
NFC Development
Andreas Jakl, Mopius

Windows 8 Platform NFC Development v2.0.0 © 2014 Andreas Jakl
NFC Forum and the NFC Forum logo are trademarks of the Near Field Communication Forum.

1

Andreas Jakl
Twitter: @mopius
Email: andreas.jakl@mopius.com
Trainer & app developer
– mopius.com
– nfcinteractor.com

Nokia: Technology Wizard
FH Hagenberg, Mobile Computing: Assistant Professor
Siemens / BenQ Mobile: Augmented Reality-Apps

2

We’re covering
Windows (Phone) 8 Proximity APIs
Based on MSDN documentation
bit.ly/ProximityAPI
bit.ly/ProximityAPIwp8
bit.ly/ProximitySpec


3

Tap and Do
A gesture that is a natural interaction between people in close proximity used
to trigger doing something together between the devices they are holding.

System: Near Field Proximity
(e.g., NFC)

Documentation: bit.ly/ProximitySpec

4

NFC Scenarios

Connect Devices

Exchange Digital Objects

Acquire Content


5

From Tags and Peers

ACQUIRE CONTENT

6

Acquire Content Scenarios
Website link (e.g., company)

Laulujoutsen
Whooper Swan
National bird of Finland,
on €1 coin

More information (e.g., museum, concert)

Custom app extensions (e.g., bonus item for a game)
Angry Birds © Rovio

7

Get Started: Read URIs via NFC
ProximityDevice
Connect to HW
Detect devices in range
Publish & subscribe to messages

ProximityMessage
Contents of received message


8

Proximity Capability


9

URI Subscriptions
1 Activate proximity device
_device = ProximityDevice.GetDefault();

2 Subscribe to URI messages
_subscribedMessageId = _device.SubscribeForMessage(
"WindowsUri", MessageReceivedHandler);

3 Handle messages
private void MessageReceivedHandler(ProximityDevice sender,
ProximityMessage message) {
var msgArray = message.Data.ToArray();
var url = Encoding.Unicode.GetString(msgArray, 0, msgArray.Length);
Debug.WriteLine("URI: " + url);
}
API documentation: bit.ly/ProximityAPI

10

URI Subscriptions
Smart Poster
WindowsUri
URI

4 Cancel subscriptions
_subscribedMessageId = _device.SubscribeForMessage(…);
_device.StopSubscribingForMessage(_subscribedMessageId);

11

Publish & Write

SPREAD THE WORD

12

Publish Messages
1 Start publishing
_publishingMessageId = _device.PublishUriMessage(
new Uri("nfcinteractor:compose"));

Proximity devices only
– (doesn’t write tags)

Contains
scheme,
platform &
App ID

Windows Protocol + URI record
– Encapsulated in NDEF


13

Write Tags
1 Prepare & convert data
var dataWriter =
new Windows.Storage.Streams.DataWriter {
UnicodeEncoding = Windows.Storage.Streams.
UnicodeEncoding.Utf16LE};
dataWriter.WriteString("nfcinteractor:compose");
var dataBuffer = dataWriter.DetachBuffer();

Mandatory
encoding

2 Write tag (no device publication)
_device.PublishBinaryMessage("WindowsUri:WriteTag", dataBuffer);

bit.ly/PublishTypes

14

Tag Size?
1 Subscribe for writable tag info
_device.SubscribeForMessage("WriteableTag",
MessageReceivedHandler);

2 Check maximum writable tag size in handler
var tagSize = BitConverter.ToInt32(message.Data.ToArray(), 0);
Debug.WriteLine("Writeable tag size: " + tagSize);

3 Device HW capabilities
var bps = _device.BitsPerSecond;
var mmb = _device.MaxMessageBytes;

// >= 16kB/s
// >= 10kB


15

Standardized NFC Tag Contents

NDEF HANDLING

16

Data on an NFC Tag
LaunchApp
Arguments
[speech text]
WindowsPhone app ID
{0450eab3-92…}

Data
NDEF Record(s)

Encapsulated in
NDEF Message

Encoded through
NFC Forum
Tag Type Platform

NDEF = NFC Data Exchange Format, Container image adapted from s_volenszki (Flickr), released under Creative Commons BY-NC 2.0

Stored on
NFC Forum Tag

17

Reading NDEF
1 Subscribe to all NDEF messages
"NDEF", MessageReceivedHandler);

2 Parse raw byte array in handler 

http://www.nfc-forum.org/specs/


18

Reading NDEF
// Convert the language code to a byte array

Simple example:
assembling payload of Text record

1 Subscribe to all NDEF messages= Encoding.UTF8;
var languageEncoding

var encodedLanguage = languageEncoding.GetBytes(languageCode);
// Encode and convert the text to a byte array
var encoding = (textEncoding == TextEncodingType.Utf8) ? Encoding.UTF8 : Encoding.BigEndianUnicode;
var encodedText = encoding.GetBytes(text);
// Calculate the length of the payload & create the array
var payloadLength = 1 + encodedLanguage.Length + encodedText.Length;
Payload = new byte[payloadLength];

"NDEF", MessageReceivedHandler);

2 Parse raw byte array in handler 

// Assemble the status byte
Payload[0] = 0; // Make sure also the RFU bit is set to 0
// Text encoding
if (textEncoding == TextEncodingType.Utf8)
Payload[0] &= 0x7F; // ~0x80
else
Payload[0] |= 0x80;

http://www.nfc-forum.org/specs/

// Language code length
Payload[0] |= (byte)(0x3f & (byte)encodedLanguage.Length);
// Language code
Array.Copy(encodedLanguage, 0, Payload, 1, encodedLanguage.Length);
// Text
Array.Copy(encodedText, 0, Payload, 1 + encodedLanguage.Length, encodedText.Length);


19

Windows 8 & Windows Phone 8

NFC / NDEF LIBRARY FOR PROXIMITY APIS

20

NDEF.codeplex.com
Create NDEF
messages & records
(standard compliant)

Reusable
NDEF classes

Parse information
from raw byte arrays

Fully documented
Open Source LGPL license
(based on Qt Mobility)


21

NDEF Subscriptions
1 Subscribe to all NDEF formatted tags
_subscribedMessageId = _device.SubscribeForMessage("NDEF",
MessageReceivedHandler);

2 Parse NDEF message
private void MessageReceivedHandler(ProximityDevice sender,
ProximityMessage message)
{
var msgArray = message.Data.ToArray();
NdefMessage ndefMessage = NdefMessage.FromByteArray(msgArray);
[...]
}

22

NDEF Subscriptions
3 Analyze all contained NDEF records with specialized classes
foreach (NdefRecord record in ndefMessage)
{
Debug.WriteLine("Record type: " +
Encoding.UTF8.GetString(record.Type, 0, record.Type.Length));
// Check the type of each record ‐ handling a Smart Poster in this example
if (record.CheckSpecializedType(false) == typeof(NdefSpRecord))
{
// Convert and extract Smart Poster info
var spRecord = new NdefSpRecord(record);
Debug.WriteLine("URI: " + spRecord.Uri);
Debug.WriteLine("Titles: " + spRecord.TitleCount());
Debug.WriteLine("1. Title: " + spRecord.Titles[0].Text);
Debug.WriteLine("Action set: " + spRecord.ActionInUse());
}
}

23

Write NDEF
1 Prepare & convert data
// Initialize Smart Poster record with URI, Action + 1 Title
var spRecord = new NdefSpRecord
{ Uri = "http://www.nfcinteractor.com" };
spRecord.AddTitle(new NdefTextRecord
{ Text = "Nfc Interactor", LanguageCode = "en" });
// Add record to NDEF message
var msg = new NdefMessage { spRecord };

2a Write tag
// Publish NDEF message to a tag
_device.PublishBinaryMessage("NDEF:WriteTag", msg.ToByteArray().AsBuffer());

2b Publish to devices
// Alternative: send NDEF message to another NFC device
_device.PublishBinaryMessage("NDEF", msg.ToByteArray().AsBuffer());

24

APP LAUNCHING

25

App Launch Scenarios
Discover your app

Share app to other users

Create seamless multi-user experience

26

App Launching Summary
Register for

Files

URI protocol

LaunchApp
Tag

Peer to Peer

User opens
particular file

Tag launches app
through custom
URI scheme

Tag directly contains
app name and
parameters

App requests peer
device to start
the same app

Not so relevant for NFC


27

How to Launch Apps

either or

Win8 + WP8

Tag directly contains
app name and
custom data.
No registration necessary.

Custom URI scheme
launches app.
App needs to register.


28

nearspeak: Good+morning.
Protocol
name

Custom
data
Encoded Launch URI
Examples*
skype:mopius?call
spotify:search:17th%20boulevard

* Definition & examples: http://en.wikipedia.org/wiki/URI_scheme

29

User Experience

No app installed

1 app installed

2+ apps installed


30

WP Protocol Association

Note: different
in Win8 / WP8

1 Specify protocol name in WMAppManifest.xml
...</Tokens>
Protocol
<Extensions>
name
<Protocol Name="nearspeak"
NavUriFragment="encodedLaunchUri=%s"
TaskID="_default" />
Fixed
</Extensions>


31


Note: different
in Win8 / WP8

2 Create UriMapper class to parse parameters
class NearSpeakUriMapper : UriMapperBase
{
public override Uri MapUri(Uri uri)
{
// Example: "Protocol?encodedLaunchUri=nearspeak:Good+morning."
var tempUri = HttpUtility.UrlDecode(uri.ToString());
var launchContents = Regex.Match(tempUri, @"nearspeak:(.*)$").Groups[1].Value;
if (!String.IsNullOrEmpty(launchContents))
{
// Launched from associated "nearspeak:" protocol
// Call MainPage.xaml with parameters
return new Uri("/MainPage.xaml?ms_nfp_launchargs=" + launchContents, UriKind.Relative);
}
// Include the original URI with the mapping to the main page
return uri;
}}

Argument already handled in step 9 of LaunchApp
tags (MainPage.OnNavigatedTo)


32

3 Use UriMapper in App.xaml.cs
(region:

)

private void InitializePhoneApplication() {
RootFrame = new PhoneApplicationFrame();
RootFrame.UriMapper = new NearSpeakUriMapper();
}

– If needed: launch protocol from app (for app2app comm)
await Windows.System.Launcher.LaunchUriAsync(
new Uri("nearspeak:Good+morning."));


33

bit.ly/AppLaunching

Windows 8 Protocol Association


34

parameters

platform 1

app name 1

platform 2

app name 2

…

Encoded into NDEF message*

Directly launch App
* For your low-level interest: type: Absolute URI, type name format: windows.com/LaunchApp. Contents re-formatted, e.g., with string lengths before each value

35

Write LaunchApp Tags

Note: different
in Win8 / WP8

1 Launch parameters, platforms + app IDs (note: Win8/WP8 ID format differences)
var launchArgs = "user=default"; // Can be empty
// The app's product id from the app manifest, wrapped in {}
var productId = "{xxx}";
var launchAppMessage = launchArgs + "tWindowsPhonet" + productId;

2 Convert to byte array
var dataWriter = new Windows.Storage.Streams.DataWriter
{UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf16LE};
dataWriter.WriteString(launchAppMessage);

3 Write to tags
_device.PublishBinaryMessage("LaunchApp:WriteTag",
dataWriter.DetachBuffer());

36

PEER TO PEER

37

Seamless MultiUser Games &
Collaboration

Tap for

Quick Data
Exchange

Long Term
Connection

ProximityDevice

PeerFinder

Exchange Windows /
NDEF messages,
SNEP protocol

Automatically builds
Bt / WiFi Direct
socket connection


38

Establishing

Trigger

Long Term
Connection
Browse

Interact with Tap

Start Search

NFC

Bt, WiFi, etc.


39

Tap to Trigger

App not installed

App installed

40

Connection State
Proximity gesture complete
Devices can be pulled away

Which device initiated tap gesture?
→ Connecting, other device Listening

1
PeerFound

2
Connecting /
Listening

Access socket of persistent transport
(e.g., TCP/IP, Bt)

3
Completed


41

Find Peers
1 Start waiting for triggered connections
PeerFinder.TriggeredConnectionStateChanged +=
TriggeredConnectionStateChanged;
PeerFinder.Start();

2 Peer found & connection established? Send message over socket
private async void TriggeredConnectionStateChanged(object sender,
TriggeredConnectionStateChangedEventArgs eventArgs) {
if (eventArgs.State == TriggeredConnectState.Completed) {
// Socket connection established!
var dataWriter = new DataWriter(eventArgs.Socket.OutputStream);
dataWriter.WriteString("Hello Peer!");
var numBytesWritten = await dataWriter.StoreAsync();
3
}}
* For URI records + simple Smart Poster (w/o title), use the WindowsUri type.

42
Completed

UX Recommendations*
User initiated peer
search only

Ask for consent

Show connection
state

Failed
connection?
Inform & revert to
single-user mode

Let user get out of
proximity
experience

Proximity: only if
connection details
not relevant

* bit.ly/ProximityUX

43

NFC Tools
Proximity Tapper for WP emulator
– http://proximitytapper.codeplex.com/

Open NFC Simulator
– http://open-nfc.org/wp/editions/android/

NFC plugin for Eclipse: NDEF Editor
– https://code.google.com/p/nfc-eclipse-plugin/

44

nfcinteractor.com


45

NFC Resources
 NFC News: nfcworld.com
 NFC developer comparison
(WP, Android, BlackBerry):
bit.ly/NfcDevCompare
 Specifications: nfc-forum.org

46

Thank You.
Andreas Jakl
@mopius
mopius.com
nfcinteractor.com


47

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