Objective-C Fundamentals

72 CHAPTER 3 An introduction to objects
The hardest challenge in providing images for each rental property in the list is
determining in which city each property is located. At this stage, you’ll be fairly naive
and split the address field on the sole semicolon it contains. In the future, you may
like to revisit this solution and find a more robust mechanism or use some of the
iPhone SDK geocoding APIs.
Using the rangeOfString: message available on the NSString class, b you can
determine the location of the semicolon in the property’s address, and by passing this
index into additional NSString methods, substringFromIndex: and substringTo-
Index:, you can separate the street address and city into two separate strings c. In
the call to substringFromIndex: you have to add 2 to the index returned by rangeOf-
String: to skip over the semicolon and the space that follows it.
Now that you’ve extracted a rental property’s city from its address, you’re ready to
determine which image to display and attach it to the table view cell d. You do this by
comparing the contents of the city variable against a couple of hardcoded city
names. Once you determine the type of location, use UIImage’s imageNamed functionality
to load the images you previously included in the application.
One obvious problem with the technique demonstrated in this revision of the Rental
Manager application is that the list of cities and their mappings to location types is hardcoded
and specified in code. This makes it difficult and more time consuming (especially
with the App Store submission process) to update the behavior of the application
as your rental portfolio expands and covers properties in other cities. Ideally, you want
to separate the logic from the data so you can easily update the city mappings without
needing to recompile or to resubmit the application: more on this in the next chapter.
3.7 Summary
Enhancing the procedural C language to have object-oriented features is essentially
what brought Objective-C to life. The benefits of developing applications in an objectoriented
manner generally far outweigh the extra effort required to learn the additional
terminology and techniques that object-orientation entails.
Chief among the advantages of object-oriented programming is an improved ability
to separate a complex application into a number of smaller, discrete building
blocks, or classes. Rather than considering a large, complex system, the developer’s
task becomes one of developing multiple smaller systems that combine and build on
top of each other to perform tasks far more complex than any one part can do alone.
The ability to package data plus logic into modules, called classes, also makes it
easier to transplant an object designed and developed in one application into
another. Application frameworks such as Cocoa Touch and Foundation Kit take this to
another level. Their sole purpose is to provide developers with a large number of
classes out of the box and ready to be put to work in their applications. Developers
need not spend time ironing out bugs and quirks in the 900th string concatenation
implementation the world has seen. Application developers can instead focus on the
distinct features of their own applications.