Objective-C Fundamentals

Declaring the interface of a class
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By sticking with conventions, you won’t rock the boat
In Objective-C it’s traditional to name methods that return the value of instance variables
the same as the instance variables themselves.. This is unlike languages such as Java
in which such methods would commonly use a “get” prefix, as in getRentalPrice.
You can name your methods using any convention you like, but by using the time-honored
Objective-C conventions, you’ll have a smoother voyage as you develop your
application. Many features of Cocoa Touch, such as Core Data, Key-Value Coding,
and Key-Value Observing, rely in part on language conventions—or at least work nicer
out of the box if these conventions are respected. If you use other conventions, you
may discover that you have additional work to do before being able to fully use all
features of Objective-C or Cocoa Touch.
the rental price. To do so, you need to specify that the method expects a parameter,
or argument:
- (void)setRentalPrice:(float)newPrice;
In a method declaration, a parameter is introduced by the colon (:) character, which
is followed by the parameter’s data type and name. In this case you’ve declared a
method called setRentalPrice:, which has a single parameter called newPrice of
type float.
It’s possible to declare a method that expects multiple parameters. For example,
you could declare a method to decrease the rental price by a fixed percentage, ensuring
it doesn’t drop below a predetermined minimum value, by declaring a method
as follows:
- (void)decreaseRentalByPercent:(float)percentage withMinimum:(float)min;
This code declares a method named decreaseRentalByPercent:withMinimum: that
accepts two parameters (percentage and min). Notice how the position of each colon
character in the name indicates where a parameter is expected and that the method
name is interspersed between the parameter declarations rather than being a single
identifier at the start of the declaration.
It’s important to realize that in a method signature, the colons aren’t optional. As
an example, the identifiers rentalPrice and rentalPrice: identify different methods.
The first accepts no parameters, while the second expects a single parameter (as
indicated by the colon). It’s possible (although rather confusing) for a class to declare
both methods.
It isn’t essential to provide a part of the method name before each parameter. For
example, the following declaration is equally valid even though no part of the method
name is provided before the last argument named min:
- (void)decreaseRentalByPercent:(float)percentage :(float)min;
This alternative method is named decreaseRentalByPercent:: and is generally considered
bad form because the name of the method is less self-documenting than