Web Services with Objective-C

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Hot New Technology
World Wide Web – WWW
Web 3.0
Rise of the Machines!!!
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Web services
Web services – Websites for programs
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Common Web Services
Flickr
Amazon
Twitter
Youtube
Ebay
Google search, maps, etc.
Meetup
Thousands of others
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2 basic styles of services
Service Oriented Architectures – (Distributed Objects)
CORBA, SOAP, XML-RPC, COM
Resource Oriented Architectures
Resources can be anything
REST – use simple web based technologies
HTTP
URI
XML (or Json, xhtml, text, plists, etc.)
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HTTP
Methods: GET, POST, PUT, DELETE, HEAD
Parameters in URL or Body
Return codes: 200, 404, 500, etc.
Headers: Cache, Authentication, etc.
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URI / URL
Addressability
Connectedness
Uniformity
Hierarchical
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Content
Format up to the designer
XML
JSON – especially for AJAX
XHTML
Can support multiple formats
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Steps for using a RESTful service
Gather information - URI, Method, Params
Make HTTP Request
Parse Result
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1) Gather information
Study the API
http://www.meetup.com/meetup_api/docs/
Decide what you want to do: Ie. Get a list of meetups near me.
http://api.meetup.com/events.xml/?lat=40.743348&lon=-73.993525&radius=1&key=123
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Result (part 1)
<results>
<head>
<count>200</count>
<total_count>1274</total_count>
<updated>Mon Aug 25 20:10:21 EDT 2008</updated>
<description>API method for accessing meetup events</description>
<lat>40.743348</lat>
<id/>
<method>Events</method>
<lon>-73.993525</lon>
<title>Meetup Events</title>
<next>
http://api.meetup.com/events/ ?...
</next>
<link>http://api.meetup.com/events/</link>
<url>
http://api.meetup.com/events/ ? …
</url>
</head>
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Result (part 2)
<items>
<item>
<lon>-73.98999786376953</lon>
<rsvpcount>3</rsvpcount>
<group_name>Better Laugh Laughter Yoga</group_name>
<lat>40.7400016784668</lat>
<feecurrency>USD</feecurrency>
<time>Mon Aug 25 19:30:00 EDT 2008</time>
<event_url>http://stress.meetup.com/12/calendar/8385325</event_url>
<attendee_count>0</attendee_count>
<id>8385325</id>
<venue_lon/>
<fee>0.0</fee>
<venue_name/>
<venue_lat/>
<description/>
<photo_url>
http://photos1.meetupstatic.com/photos/event/1/6/4/b/global_3743707.jpeg
</photo_url>
<updated>Mon Jul 21 20:35:17 EDT 2008</updated>
<feedesc/>
<questions/>
<name>Better Laugh Laughter Yoga Meetup</name>
</item>
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2) Make HTTP Request
Encode parameters URL or body
Specify method
Manipulate headers
Example: Simple GET in your browser or use curl
curl "http://api.meetup.com/groups/?zip=10003&key=123”
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Simplest way in Objective-C
NSString *urlString =
@"http://api.meetup.com/…”;
NSURL *url = [NSURL URLWithString:urlString];
NSStringEncoding encoding;
NSError *error;
NSString *doc = [NSString stringWithContentsOfURL:url usedEncoding:&encoding error:&error];
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More control
NSURLResponse *response;
NSError *error;
NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];
// Manipulate the request
NSData *urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];
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Asynchronous way
NSURLConnection *connection = [NSURLConnection connectionWithRequest:urlRequest delegate:self];
// start ‘progress’ animation
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[myData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// stop ‘progress’ animation and use data.
}
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Homework
Extract this all out into a reusable web services client class that
Sets parameters and body based on HTTP method
Makes asynchronous calls and collects data
Calls back arbitrary methods on delegate
Load images asynchronously also
Hints: SEL/performSelector, also check out twitter engine
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3) Parse Results
NSXMLParser - SAX based parsing
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
[parser parse];
parser: didStartElement: namespaceURI: qualifiedName: attributes:
parser: didEndElement: namespaceURI: qualifiedName:
parser: foundCharacters:
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Other Options
Libxml2
http://code.google.com/p/touchcode/wiki/TouchXML
http://code.google.com/p/touchcode/wiki/TouchJSON
P Lists – NSPropertyListSerialization propertyListFromData
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Things to look out for
Bugs in client libraries - sometimes PUT and DELETE are not well supported
Debugging the HTTP request response can be trying. Anyone know of a good debugging proxy?
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Resources
programmableweb.com
Code besides twitter engine?
For REST info check out:
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Questions?
Slides will be on http://www.E-String.com
Feel free to contact me:
Julio Barros
917-445-7264
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Web Services with Objective-C

by Juio Barros

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