CSCI 251: iphone Application Development

Transcription

1 CSCI 251: iphone Application Development Spring Term 2012 Lecture #3: Handling Data (Chater 8)

2 Handling Data (from the Internet) Handling XML (structured data formatted as text) Handling (unformatted) text via regular expressions

3 Why XML? Problem: Most of the phenomena we deal with have internal structure, but computers transmit data serially (one byte at a time) class Room: def init (self, w, l, c): self.width = w self.length = l self.contents = c class House: def init (self, rs, w, l): self.rooms = rs; self.lawnwidth = w self.lawnlength = l kitchen = Room(24.5, 10.6, ['fridge', 'stove']

4 XML: A Brief History SGML (late 1980s): standardized general markup language for documents HTML (1991): hypertext markup language for the web XML formalized in 1998 HTML XML: HTML is not a subset of HTML, so XML parsers don't necessarily handle HTML!

5 XML: Deeper History Context-Free Grammars (N. Chomsky, 1950s): ability to express syntactic relationships across arbitrarily long distances

6 XML: Deeper History Context-Free Grammars (N. Chomsky, 1950s): ability to express syntactic relationships across arbitrarily long distances That guy likes you.

7 That guy you ran into last night likes you.

8 That guy you ran into last night at FD likes you.

9 That guy you ran into last night at FD standing around with a group of his friends likes you.

10 if x < y: print 'foo' else: print 'bar'

11 if x < y: if x > z: print 'foo' else: print 'oof' else: print 'bar'

12 Grammars if COND else COND > NUM x NUM etc.

13 Derivation

14 Derivation

15 Derivation COND if else

16 Derivation COND if > else

17 Derivation COND if > else

18 Derivation COND if x > else

19 Derivation COND NUM if x > else

20 Derivation COND NUM if x > else

21 Derivation COND NUM if x > else

22 Derivation COND NUM if x > x else

23 Derivation COND NUM if x > x else

24 Derivation COND NUM if x > x else y

25 Parsing if x > x else y

26 Parsing: Bottom-Up NUM if x > x else y

27 Parsing: Bottom-Up NUM if x > x else y

28 Parsing: Bottom-Up COND NUM if x > x else y

29 Parsing: Bottom-Up COND NUM if x > x else y

30 Parsing: Top-Down if x > x else y

31 Parsing: Top-Down COND if x > x else y

32 Parsing: Top-Down COND if x > x else y

33 Parsing: Top-Down COND NUM if x > x else y

34 Parsing: Top-Down COND NUM if x > x else y

35 Basic XML Grammar ELEMENT <TAG> ELEMENT </ TAG> ELEMENT <TAG /> TAG name ATTRIBUTES ATTRIBUTES ATTRIBUTE ATTRIBUTES ATTRIBUTES ATTRIBUTE ATTRIBUTE name = " value "

36 XML Parsing Strategies DOM: Document Object Model Reads entire document, building a parse tree Tree can then be queried using XPath query language SAX: Simple API for XML Event-driven: reads XML document sequentially, responding to each tag with a delegate method Fast, efficient, uses less memory

37 We'll use DOM NSXMLDocument class is part of the Foundation Framework, but not available for iphone (except in simulator) So author suggests using libxml2 library, via Matt Gallagher's XPath wrappers.

38 WeatherForecast: NSObject { // Parent View Controller MainViewController *viewcontroller; // Google Weather Service NSMutableData *responsedata; NSURL *theurl; } //...

39 libxml2/xpath #import "WeatherForecast.h" #import "MainViewController.h" #import WeatherForecast { -(void)connection:(nsurlconnection *)connection didreceivedata:(nsdata *)data { } [responsedata appenddata:data]; -(void)connectiondidfinishloading:nsurlconnection *)connection { //... NSString *xpathquerystring; NSArray *nodes; xpathquerystring nodes = PerformXMLPathQuery(responseData, xpathquerystring); //...

40 JSON JavaScript Object Notation: A lightweight alternative to XML Used by Twitter API Objective-C support at

41 { } "trends":[ { "name":"jick Nonas", "url":" }, { "name":"#stoptalkingabout", "url":" }, { "name":"#fanofafan", "url":" },... ], as_of":"mon, 17 May :30: "

42 #import <JSON/JSON.h> //... - (void)connectiondidfinishloading:(nsurlconnection *)connection { NSString *content = [[NSString alloc] initwithbytes:[responsedata bytes] length:[responsedata length] encoding:nsutf8stringencoding]; SBJSON *parser = [[SBJSON alloc] init]; NSDictionary *json = [parser objectwithstring:content]; NSArray *trends = [json objectforkey:@"trends"]; for (NSDictionary *trend in trends) { [viewcontroller.names addobject:[trend objectforkey:@"name"]]; [viewcontroller.urls addobject:[trend objectforkey:@"url"]]; } [parser release]; } //...

43 Regular Expressions Recall grammar rules for simple expressions: x NUM TAG anything Expressions like these, which do not involve longdistance dependencies, can be described by a simpler kind of mechanism called regular expressions.

44 Regular Expressions Regular expressions can 1. Put one thing after another: e.g., a variable consists of letter followed by some other stuff 2. Repeat things: e.g., any sequence (repetition) of characters is a valid identifier 3. Provide a choice: e.g., an identifier can start with a letter or an underscore.

45 Regular Expressions Different packages use different notation, but there is some commonality In the package used in the book, substring matching is the default, so e.g. 234 matches 1234.

46 Other notation: ^ beginning of string: ^123 matches 1234 but 0123 not $ end of string: 234$ matches 1234 but not 123 * matches zero or more times: \d (\D) matches any (non)numeric character \s (\S) matches a (non)whitespace character \w (\W) matches a (non)alphanumeric-or-underscore character

47 RegexKitLite Extends NSString class via Objective-C's category mechanism (something we didn't discuss) #import "RegexKitLite.h" //... NSString *string is a string"; NSString *match = [string stringbymatching:@"a string$" capture:0]; // first occurrence NSLog(@"%@", match);

48 RegexKitLite #import "RegexKitLite.h" //... NSString *string2 is a string"; NSString *regexstring string$"; NSString *replacementstring string"; NSString *newstring = [string2 stringbyreplacingoccurrencesofregex:regexstring withstring:replacementstring] NSLog(@"%@", newstring);

49 Storing Data As on any platform, we need a way to save data files to disk for later retrieval. Sandboxed file system: each app has access to its own Documents folder and no other folders (modulo jailbreaking) Two approaches Flat text files SQLite

50 Flat Files First we get the the app's Document directory: NSArray *arraypaths = NSSearchPathForDirectoriesInDomains( NSDocumentDirectory, NSUserDomainMask, YES); NSString *docdirectory = [arraypaths objectatindex:0];

51 Flat Files Then we can write data to a file: NSString *string World"; NSString *filepath = [docdirectory stringbyappendingstring:@"/file.txt"]; [string writetofile:filepath atomically:yes encoding:nsutf8stringencoding error:nil];

52 Flat Files To read text data from a file: NSString *filecontents = [NSString stringwithcontentsoffile:filepath encoding:nsutf8stringencoding error:nil]; NSLog(@"%@", filecontents); We could probably combine flat files with XML to store and retrieve simple (non-binary) data types. For binary data (images, sounds), we turn to...

53 Storing Information in an SQL Database Structured Query Language: Most popular language for databases SQLite library comes with iphone SDK, with support for integer, real, text, and BLOB (Binary Large Object) types (e.g., images) sqlite3 command-line utility creates empty database eatblob command-line utility (from sourceforge) adds data to database sqlite3_ C functions allow you to access the database in your app code