CODEWITHSUNDEEP
objective-cinitializationdeclared-property
felix
felix

Reputation: 11552

Why the setter is called for one property but not the other?

I took this code from the Big Nerd Ranch iOS Programming book. In the code, they are assigning two instance variables, coordinate and title. Why is coordinate assigned directly, and title is set by calling a setter?

Header File

@interface BNRMapPoint : NSObject<MKAnnotation>

  -(id)initWithCoordinate:(CLLocationCoordinate2D )c title:(NSString *)t;

  @property(nonatomic, readonly) CLLocationCoordinate2D coordinate;
  @property(nonatomic, copy)  NSString *title;

@end

Implementation File

-(id)initWithCoordinate:(CLLocationCoordinate2D)c title:(NSString *)t
{
    self = [super init];
    if(self){
        coordinate = c;
        [self setTitle:t];
    }
    return self;
}

Upvotes: 1

Views: 131

Answers (2)

FeifanZ
FeifanZ

Reputation: 16316

There is a school of thought that says you should copy NSStrings. They're invoking the setter on the string to get that copy. However, there's no need to copy (or even retain) the coordinate, as Josh points out.

Upvotes: 0

jscs
jscs

Reputation: 64002

Two reasons, the most important of which is that there is no setter for the coordinate property. It's declared read-only, so there is only a getter method generated.

The second is that CLLocationCoordinate2D is a struct, not an object. There are memory management actions (copying, in this case) that have to be taken for the title object; the simplest way to make that happen is to use the already-existent setter method. The compiler takes care of moving the data for a POD type like CLLocationCoordinate2D.

If the second were the only reason, however, this would be a poor decision -- that's bad style to use the setter for one property and not for the other.

Upvotes: 1

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