Objective-C Fundamentals

158 CHAPTER 7 Protocols
sets a title here, this button fits the actionSheetCancel: method. It’s commonly red
(you can see it in the contacts section of the iPhone), and is used to confirm actions
such as deleting data or logging off:
- (void)actionSheetCancel:(UIActionSheet *)actionSheet
7.3.4 NSXMLParser
The final protocol we review differs slightly from the protocols we already covered.
Apple provides a class to iPhone developers called NSXMLParser. Developers use this
class when parsing XML. It should be noted that several open source alternatives to
NSXMLParser are available and used by many developers, but for the sake of consistency,
we look at the delegate methods of the standard Cocoa XML Parser.
There is no protocol; you’ll receive no warning if you don’t declare
this in the header of the application you’re creating. NSXMLParser is a fringe design
class that follows the principles of protocol design but doesn’t explicitly define a protocol.
An NSXMLParser object, like the other objects, has a parameter called delegate
that must be defined. Any object defined as the delegate has the option of implementing
and collecting 20 different delegate methods. NSXMLParser provides delegate
methods that handle every point of parsing for both XML- and Document Type Definition
(DTD)-based documents.
XML is a type of file that can hold data in a very structured manner. As a quick introduction,
XML uses syntax similar to HTML in order to create unique data structures. An
example of an XML element to describe a person is shown in the following listing.
Listing 7.10
An author in XML
Collin Ruffenach
23
male
Objective C for the iPhone
2010
intermediate
XML is a common means of getting data from online sources such as Twitter. XML is
also used to facilitate the data required to run your specific iPhone project. iOS development
relies heavily on plist files. These files are really just XML and are used by
Xcode to get things like your icon name and other application data. Xcode handles
the setup of these values.
DTD is a document that describes the structure of the XML that you’re working
with. The DTD for the XML in listing 7.10 would be the following: