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

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