Objective-C Fundamentals

Creating and destroying objects
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correctly configure the object. Typically, a class provides one or more specialized initialization
methods. These methods are commonly named using the form initWith-
XYZ:, where XYZ is replaced with a description of any additional parameters required
to properly initialize the object.
As an example, add the following method declaration to the @interface section of
the CTRentalProperty class:
- (id)initWithAddress:(NSString *)newAddress
rentalPrice:(float)newRentalPrice
andType:(PropertyType)newPropertyType;
This instance method enables you to provide a new address, rental price, and property
type for the object about to be initialized. The next step is to provide an implementation
for the method in the @implementation section of the CTRentalProperty
class. Do this by adding the following code.
Listing 5.5
Implementing a custom initialization method for CTRentalProperty
- (id)initWithAddress:(NSString *)newAddress
rentalPrice:(float)newRentalPrice
andType:(PropertyType)newPropertyType
{
if ((self = [super init])) {
self.address = newAddress;
self.rentalPrice = newRentalPrice;
self.propertyType = newPropertyType;
}
}
return self;
The main part of this method sets the various properties of the object to the new values
specified by the parameters. There are, however, a couple of additional features in
this listing that deserve extra attention.
The if statement performs a number of important steps in a single, condensed
line of source code. Working from right to left, it first sends the init message to
super. super is a keyword, similar to self, that enables you to send messages to the
superclass. Before you initialize any of your own instance variables, it’s important to
provide your superclass a chance to initialize its own state.
The object returned by the superclass’s init method is then assigned to self in
case it has substituted your object for another. You then check this value to ensure it
isn’t nil, which would indicate the superclass has determined it can’t successfully initialize
the object. If you prefer, you could expand these steps into two separate statements,
as follows:
self = [super init];
if (self != nil) {
...
}