Many Apps need to access data online. This talk discusses problems and solutions when accessing remote data with Android and iPhone. After a brief review of a number of frameworks, an approach is outlined to implement data access in a cross-platform manner using a DSL.

1. Cross-Platform Data Access
for iPhone and Android
MobileTechCon 2011 March 28th - 30th, Munich
(c) 2011 @peterfriese / @itemismobile

2. cell phone usage is ubiquitous

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5. many services only make sense
when connected to the web

6. People are !fferent

7. ... so #ey have !fferent ta$es!

8. countless devices

9. diversity of platforms

10. Problems Solutions

11. (Missing) Connectivity

12. Solution: Detect Connectivity

13. Detecting Connectivity
States we need to detect:
Device not connected to internet
Connection slow
Server(s) not reachable
Server online, but requested service not available

14. Detecting Connectivity
iPhone Reachability
hostReach = [[Reachability
reachabilityWithHostName:@"www.apple.com"] retain];
[hostReach startNotifier];
[self updateInterfaceWithReachability: hostReach];
!
internetReach = [[Reachability
reachabilityForInternetConnection] retain];
[internetReach startNotifier];
[self updateInterfaceWithReachability: internetReach];
wifiReach = [[Reachability reachabilityForLocalWiFi] retain];
[wifiReach startNotifier];
[self updateInterfaceWithReachability: wifiReach];
http://developer.apple.com/library/ios/#samplecode/Reachability/

15. Detecting Connectivity
Android ConnectivityManager
ConnectivityManager connectivity =
(ConnectivityManager) getSystemService
(Context.CONNECTIVITY_SERVICE);
NetworkInfo wifiInfo =
connectivity.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
NetworkInfo mobileInfo =
connectivity.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
http://developer.android.com/reference/android/net/ConnectivityManager.html

16. Different Data Formats
Proprietary
XML
SOAP
JSON

17. Solution: Use Different Parsers

18. A Fine Selection of Parsers
XML
SAXParser - (Android SDK)
DocumentBuilder - (Android SDK)
XmlPullParser - (Android SDK)
JSON
JSONTokener - (Android SDK)
JSON Simple - http://code.google.com/p/json-simple/
Jackson - http://jackson.codehaus.org/
GSon - http://code.google.com/p/google-gson/

19. Parsing JSON
Gson
public T transform(InputStream inputStream) {
InputStreamReader reader = new InputStreamReader(inputStream);
BufferedReader buffered = new BufferedReader(reader);
Gson gson = new Gson();
Type clazz = getGenericType();
T results = gson.fromJson(buffered, clazz);
try {
buffered.close();
reader.close();
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
return results;
}
private Type getGenericType() {
Type type = ((ParameterizedType)getClass()
.getGenericSuperclass()).getActualTypeArguments()[0];
return type;
}

20. A Fine Selection of Parsers
XML
NSXMLParser - (iPhone SDK)
libxml2 - (iPhone SDK)
TouchXML - https://github.com/TouchCode/TouchXML
GDataXML - http://code.google.com/p/gdata-objectivec-
client/
JSON
TouchJSON - https://github.com/TouchCode/TouchJSON
json-framework - http://stig.github.com/json-framework/
YAJL - https://github.com/lloyd/yajl
JSONKit - https://github.com/johnezang/JSONKit

21. Parsing JSON
JSONKit
#import "JSONKit.h"
/...
- (id)transform:(NSString *)sourceString {
! id input = [sourceString objectFromJSONString];
id result = nil;
if ([input isKindOfClass:[NSArray class]]) {
result = [self transformArray:input];
}
else if ([input isKindOfClass:[NSDictionary class]]) {
result = [self transformDictionary:input];
}
return result;
}

22. Data Quality

23. Solution: Massage Data

24. Massaging !!
In-App vs. Online
In-App massaging:
- needs to be rewritten for each platform
- ad-hoc enhancements virtually impossible (iPhone)
Server-side massaging:
- write once, re-use with every app
- problem with authentication (man-in-the-middle)

25. Massaging
Online tools
FeedSanitizer - http://feedsanitizer.appspot.com/
HTML Tidy - http://infohound.net/tidy/
JSONFormatter - http://jsonformatter.curiousconcept.com/
Roll your own
YQL - http://developer.yahoo.com/yql/
Node.js - http://nodejs.org/
Google App Engine - http://code.google.com/appengine/

26. Massaging with
var sponsorImageExpr = /Sponsored by:.*<img.*src="(.*)">?/;
var sponsoredByFilter = new SimpleFilter(function(data) {
! session = data;
! if (session.title.match(sponsorImageExpr)) {
! ! sponsorlogoURL = session.title.match(sponsorImageExpr);
! ! session.sponsorLogoURL = sponsorlogoURL[1];
! ! session.title = session.title.replace(
sponsorImageExpr, '');!!
! }
! return session;
});
var stripHTMLFilter = new SimpleFilter(function(string) {
! return string.replace(/</?[^>]+(>|$)/g, '');
});
var sessionsFilterChain =
! new FilterChain()
! ! .append(sponsoredByFilter)
! ! .append(stripHTMLFilter);

27. Massaging with
app.get('/sessions.:format', function(request, response) {
! var isXML = (request.params.format == 'xml');
! dataProvider.getAllSessions(function(sessions) {
! ! if (isXML) {
! ! ! response.header("Content-Type", "text/xml");
! ! ! response.render('sessions.ejs',
{ layout: false,
locals: { sessions: sessions }
});
! ! }
! ! else {
! ! ! response.header("Content-Type", "application/json");
! ! ! response.send(JSON.decycle(shallow(sessions, 3)));
! ! }! !
! });
});

28. Offline Data Access

29. Solution: Use Caching

30. Caching
Store in a local SQL database
SQLite - (Android SDK)
OrmLite - http://ormlite.com/
db4o - http://db4o.com/
ActiveAndroid - https://www.activeandroid.com/
AndroidActiveRecord -
http://code.google.com/p/android-active-record/
Store in the local file system
Use cache directory - Context.getCacheDir()

31. Caching
Store in a local SQL database
SQLite - (iPhone SDK)
ActiveRecord - https://github.com/aptiva/activerecord
CoreData - (iPhone SDK)
Store in the local file system
URLCache sample - http://developer.apple.com/
library/ios/#samplecode/URLCache

32. Putting it all together

33. Solution: Data Access Frameworks

34. Features
Handle spotty connectivity
Support multiple data formats (XML / JSON)
Massage data
Provide offline data access
Map data to language concepts

35. Data Access
Frameworks
ActiveAndroid - https://www.activeandroid.com/
AndroidActiveRecord -
http://code.google.com/p/android-active-record/
RESTProvider -
https://github.com/novoda/RESTProvider

36. Data Access
Frameworks / Features
Flex. Mapping
Connectivity
Caching
JSON
XML
ActiveAndroid ! ! ! " "
AndroidActiveRecord ! ! ! " "
RESTProvider # " " #* "
* experimental

37. Data Access
Frameworks / Features
Flex. Mapping
Connectivity
Caching
JSON
XML
ce
sis ten
ActiveAndroid ! ! ! " er
P" Ws
F
AndroidActiveRecord ! ! ! " "
RESTProvider # " " #* "
* experimental

38. Data Access
RESTProvider
public class TwitterFeedExample extends ListActivity {
@Override public void onCreate(Bundle b) {
super.onCreate(b);
CPAsyncHandler g = new CPAsyncHandler(getContentResolver());
g.startQuery(1, null, Uri.parse("content://novoda.rest.test.twitter"),
null, "q=?", new String[] { "droidcon" }, null);
}
private class CPAsyncHandler extends AsyncQueryHandler {
@Override
protected void onQueryComplete(int token, Object cookie, Cursor c) {
super.onQueryComplete(token, cookie, c);
setListAdapter(new SimpleCursorAdapter(TwitterFeedExample.this,
android.R.layout.simple_list_item_2, c, new String[] {
"from_user", "text" }, new int[] {
android.R.id.text1, android.R.id.text2 }));
}
}
}

39. Data Access
Frameworks
iPhone on Rails - http://iphoneonrails.com/
CoreResource - http://coreresource.org/
RestKit - http://restkit.org/

40. Data Access
Frameworks / Features
Flex. Mapping
Connectivity
Caching
JSON
XML
iPhoneOnRails # " " ! "
CoreResource " " " " "
RESTKit " " " " "

41. Data Access
RESTKit
- (void)loadContact {
RKObjectManager* manager = [RKObjectManager
objectManagerWithBaseURL:@"http://restkit.org"];
[manager loadObjectsAtResourcePath:@"/contacts/1"
objectClass:[Contact class]
delegate:self]
}
// RKObjectLoaderDelegate methods
- (void)objectLoader:(RKObjectLoader*)objectLoader
didLoadObjects:(NSArray*)objects
{
Contact* contact = [objects objectAtIndex:0];
NSLog(@"Loaded Contact ID #%@ -> Name: %@,
Company: %@", contact.id, contact.name, contact.company);
}

42. Plethora of Languages
?@#!
Objective-C
C# Java
JavaScript

43. Solution: Use A DSL

44. Solution: Use A DSL
Entities
Data View
Mappers Controllers
Entity
Descriptions
DSL
iOS / Objective-C
describes data
model and
mapping rules
Entities
DSL IDE
Transformers Activities
Content
Providers
Android / Java

45. DSL Sample
Fetching Blog Items
entity BlogItem {
String guid
String title
String link
String description
String creator
}
contentprovider Blogposts
returns BlogItem[]
fetches XML
from (FEEDSANITIZER_URL "/sanitize?url=http%3A%2F%2Fblogs.itemis.de%2F
%3Fshowfeed%3D1&format=rss")
selects "rss.channel.item"

48. http://mobile.itemis.de
@peterfriese | http://peterfriese.de

49. Image credits
Tower bridge - http://www.flickr.com/photos/anirudhkoul/3499471010/
Little girl with cell - http://www.flickr.com/photos/spitzgogo/286917522/
Gray-haired guy on bench - http://www.flickr.com/photos/mr_t_in_dc/5524143121/
Girl with hoody, texting - http://www.flickr.com/photos/lanier67/2979124681/
Fast girl on bike - http://www.flickr.com/photos/pixel_addict/465394708/
NY Apple Store - http://www.flickr.com/photos/smoovey/3749038495/
Guy driving and texting - http://www.flickr.com/photos/lord-jim/4794895023/
Portraits:
http://www.flickr.com/photos/46914331@N03/4312184861/
http://www.flickr.com/photos/pagedooley/4258558487/
http://www.flickr.com/photos/yuri-samoilov/4105603525/
http://www.flickr.com/photos/adriel_socrates/5560606768/
http://www.flickr.com/photos/adriel_socrates/5560592742/in/photostream/
http://www.flickr.com/photos/kkoshy/4729866481/
http://www.flickr.com/photos/pagedooley/4258558741/
http://www.flickr.com/photos/mescon/3668279183/
http://www.flickr.com/photos/mescon/2984454695/
http://www.flickr.com/photos/ter-burg/428205830/
http://www.flickr.com/photos/eudaimos/2107219904/
Mountains, Lake and Boat - http://www.flickr.com/photos/visulogik/2180603155/
Dead Sea Scrolls - http://www.flickr.com/photos/kjfnjy/5249145754/
Lines of communication - http://www.flickr.com/photos/ruudhein/4442182264/
Satellite dish - http://www.flickr.com/photos/26652703@N02/2502519971/