Objective-C Fundamentals

122 CHAPTER 5 Creating classes
}
cell.textLabel.text = address;
NSString *imageName =
[cityMappings objectForKey:city];
cell.imageView.image =
[UIImage imageNamed:imageName];
cell.detailTextLabel.text =
[NSString
stringWithFormat:@"Rents for $%0.2f per week",
property.rentalPrice];
return cell;
- (void)dealloc {
[cityMappings release];
[properties release];
[super dealloc];
}
@end
The first change found in RootViewController.m is the importation of the CTRental-
Property.h header file B via an #import statement. This statement requests that the
Objective-C compiler read the contents of the specified file and interpret it as if its contents
were written directly at the point of the #import statement. In other words, this
line makes the compiler aware of the definition of the CTRentalProperty class and
allows you to use it. Without this line, the compiler wouldn’t know about the existence
of the CTRentalProperty class—at least, not while compiling RootViewController.m.
e
Release the
memory
d
Update
the
method
What about #include? What’s this nonstandard #import?
If you have knowledge of C or C++, you may know that C-based languages traditionally
use an #include statement to include the contents of another file. Objective-C, by
contrast, introduced and recommends the use of the #import statement.
The difference in behavior is subtle. If two #include statements specify the same
file, the compiler will probably complain that it has seen multiple definitions for the
classes and type definitions found in the file. This is because the #include statement
reads the contents of the specified file and passes it to the Objective-C compiler.
With multiple #include statements for the same file, the compiler sees the
source code multiple times.
The #import statement, on the other hand, has slightly more smarts to it. If a second
#import statement is found for the same file, it is, in effect, ignored. This means the
contents of the header file are seen only once by the compiler, no matter how many
times they’re requested to be imported.
#import is similar to #pragma once and other such solutions that many C and C++
compilers support as extensions to provide similar convenience.
The next major change is found in viewDidLoad c. When your Rental Manager
application first becomes visible, you create a new NSArray object and populate it with