1. In Touch with Things:
Programming NFC on Android with MORENA
Kevin Pinte
Andoni Lombide Carreton
Wolfgang De Meuter
Droidcon
April 10, 2013
Berlin, Germany

2. RFID in Android
• NFC (touch range).
NdefMessage: {
• Callback on activities ,
to detect RFID tags
with subscribed MIME- , NdefRecord
type in memory. byte array
}
• File access abstraction
read write

3. Drawbacks of the Android NFC API
• Manual failure handling
failures are the rule rather than the exception:
NFC causes A LOT of failures because of its hardware characteristics
• Blocking communication
Android documentation recommends to use a separate thread
for many NFC operations
• Manual data conversion
• Tight coupling with activity-based architecture

4. Lessons Learnt from Previous Ambient-Oriented
Programming Research
• Using objects as first class software representations for RFID-tagged “things”
is a nice abstraction.
• These objects can be directly stored in the RFID tags’ memory to minimize
data conversion.
• Event-driven discovery (fortunately built-in into Android).
• Asynchronous, fault tolerant reads and writes.
experimental scripting
language for mobile apps
in ad hoc networks
RFID tags as “mobile
devices” and I/O as
network communication

5. MORENA Middleware Architecture
Application
Thing level One middleware
for Android 4.0
or higher (API 14)
Tag level
Android

6. Evaluation: Wi-Fi Sharing Application

7. Evaluation: Wi-Fi Sharing Application

8. Things
From now on, we don’t
public class WifiConfig extends Thing { have to worry about the
public String ssid_;
activity anymore.
public String key_;
public WifiConfig(ThingActivity<WifiConfig> activity, String ssid, String key) {
super(activity);
ssid_ = ssid;
key_ = key;
}
public boolean connect(WifiManager wm) {
// Connect to ssid_ with password key_
};
Supported serialization:
}
- JSON-serializable fields.
- Skipping transient fields.
- Deep serialization, no cycles.

9. Initializing Things
As soon as an empty
tag is detected
@Override
public void whenDiscovered(EmptyRecord empty) {
empty.initialize(
myWifiThing,
new ThingSavedListener<WifiConfig>() {
@Override
public void signal(WifiConfig thing) {
toast("WiFi joiner created!");
}
},
new ThingSaveFailedListener() {
@Override
public void signal() {
toast("Creating WiFi joiner failed, try again.");
}
},
5000);
}

10. Discovering and Reading Things
As soon as a WifiConfig
tag is detected
@Override
public void whenDiscovered(WifiConfig wc) {
toast("Joining Wifi network " + wc.ssid_);
wc.connect();
}
Contains cached fields for
synchronous access.
Physical reads must be
asynchronous.

11. Saving Modified Things
myWifiConfig.ssid_ = "MyNewWifiName";
myWifiConfig.key_ = "MyNewWifiPassword";
myWifiConfig.saveAsync(
new ThingSavedListener<WifiConfig>() {
@Override
public void signal(WifiConfig wc) {
toast("WiFi joiner saved!");
}
},
new ThingSaveFailedListener() {
@Override
public void signal() {
toast("Saving WiFi joiner failed, try again.");
}
},
5000);

12. Broadcasting Things to Other Phones
Will trigger whenDiscovered on the
receiving phone with the broadcasted thing
myWifiConfig.broadcast(
new ThingBroadcastSuccessListener<WifiConfig>() {
@Override
public void signal(WifiConfig wc) {
toast("WiFi joiner shared!");
}
},
new ThingBroadcastFailedListener<WifiConfig>() {
@Override
public void signal(WifiConfig wc) {
toast("Failed to share WiFi joiner, try again.");
}
},
5000);

13. Evaluation: WiFi Sharing Application

14. MORENA Middleware Architecture
Application
Thing level One middleware
for Android 4.0
Tag level or higher (API 14)
Android

15. Detecting RFID Tags
private class TextTagDiscoverer extends TagDiscoverer {
@Override
public void onTagDetected(TagReference tagReference) {
readTagAndUpdateUI(tagReference);
}
@Override
public void onTagRedetected(TagReference tagReference) {
readTagAndUpdateUI(tagReference);
}
}
new TextTagDiscoverer(
currentActivity,
TEXT_TYPE,
new NdefMessageToStringConverter(),
new StringToNdefMessageConverter());

16. The Tag Reference Abstraction

17. Reading RFID Tags
tagReference.read(
new TagReadListener() {
@Override
public void signal(TagReference tagReference) {
// tagReference.getCachedData()
}
},
new TagReadFailedListener() {
@Override
public void signal(TagReference tagReference) {
// Deal with failure
}
});

18. Writing RFID Tags
tagReference.write(
toWrite,
new TagWrittenListener() {
@Override
public void signal(TagReference tagReference) {
// Handle write success
}
},
new TagWriteFailedListener() {
@Override
public void signal(TagReference tagReference) {
// Deal with failure
}
});

19. Fine-grained Filtering
private class TextTagDiscoverer extends TagDiscoverer {
@Override
public void onTagDetected(TagReference tagReference) {
readTagAndUpdateUI(tagReference);
}
@Override
public void onTagRedetected(TagReference tagReference) {
readTagAndUpdateUI(tagReference);
}
@Override
public boolean checkCondition(TagReference tagReference) {
// Can be used to apply a predicate
// on tagReference.getCachedData()
}
}

20. MORENA Conclusion
• Event-driven discovery.
• Non-blocking communication:
• Things: cached copy, asynchronous saving of cached data.
• TagReferences: first class references to RFID tags offering asynchronous
reads and writes.
• Automatic data conversion
• Looser coupling from activity-based architecture

21. Current Research: Volatile Database
• Data structures over many tags?
• Querying collections of things?
• Stronger consistency guarantees?
• Transactions?
• Validations?
• ... Active Record (RoR)
for RFID

22. Thing Associations
defmodel: Shelf properties: {
number: Number
} associations: {
hasMany: `books a shelf contains many books
};
defmodel: Book properties: {
title: Text;
authors: Text;
isbn: Text;
} proto: {
def isMisplaced(currentShelf) {
shelf != currentShelf;
};
} associations: {
belongsTo: `shelf a book belongs to exactly
}; one shelf in the library

23. Instantiating a Model and Saving to Tag
def newBook := Book.create: {
title := “Agile Web Development with Rails”;
authors := “Dave Thomas, ...”;
isbn := “978-0-9776-1663-3”;
};
def saveReq := newBook.saveAsync(10.seconds);
when: saveReq succeeded: {
// the book was saved to a tag
} catch: { |exc|
// book could not be saved within 10 sec
};
newBook.shelf := shelf42;
associate a book with a shelf:
shelf42.books << newBook;
foreign key in book thing

24. Working with Many Things: Reactive Queries
finding misplaced books in a library
def shelf42 := Shelf.all.first: { |s| s.number == 42 };
def currentShelf := Shelf.all.last;
most recently scanned shelf
def misplacedBooks := Book.all.where: { |b|
b.isMisplaced(currentShelf)
}; all books not matching the
last scanned shelf
misplacedBooks.each: { |b|
b.shelf := currentShelf;
b.saveAsync(5.seconds)
};
synchronize misplaced books
with current shelf

25. In Touch with Things:
Programming NFC on Android with MORENA
tinyurl.com/morena-android
tinyurl.com/kevinpinte
kevin.pinte@vub.ac.be
@bommasaurus
code.google.com/p/ambienttalk
soft.vub.ac.be/amop
@ambienttalk
Droidcon, April 10, 2013, Berlin, Germany