MapKit and Text Input - iOS Programming: The Big Nerd Ranch Guide - page 173

The protocol defines coordinate as a read-only property, which means there is a meth-
od named coordinate that returns a CLLocationCoordinate2D . While most
methods declared in the MKAnnotation protocol are optional, the coordinate meth-
od is required.
Switch to BNRMapPoint.m . (The keyboard shortcut for switching between the header
file and the implementation file is Command-Control-Up arrow.) Synthesize the proper-
ties and add the implementation for the initializer.
#import "BNRMapPoint.h"
@implementation BNRMapPoint
@synthesize coordinate, title;
- (id)initWithCoordinate:(CLLocationCoordinate2D)c title:(NSString *)t
{
self = [super init];
if (self) {
coordinate = c;
[self setTitle:t];
}
return self;
}
@end
Per our initializer rules from Chapter 2 , override init in BNRMapPoint.m to call the
new designated initializer. (This method may already be implemented by the template, so
make sure to replace its contents if that is the case.)
- (id)init
{
return [self initWithCoordinate:CLLocationCoordinate2DMake(43.07, -89.32)
title:@"Hometown"];
}
In our code, we declared coordinate as a readonly property just like the protocol
does. But we didn't have to. We could have just implemented a coordinate method
that returns a CLLocationCoordinate2D . The MKAnnotation protocol, like all
protocols, only dictates method signatures. As long as the signatures match exactly, the
conforming class can implement them however it wants.
As implemented, BNRMapPoint will return the values of its instance variables ( co-
ordinate and title ) when sent the messages coordinate and title from the
MKAnnotation protocol. However, those methods could return a constant value or per-
form some logic, as in the following implementation:
- (NSString *)title