A Brief Overview of MKAnnotation protocol

PlaceMark.h

//
//  PlaceMark.h
//  Nina
//
//  Created by Ian MacKinnon on 11-08-22.
//  Copyright 2011 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>
#import "Perspective.h"
#import <CoreLocation/CoreLocation.h>

@interface PlaceMark : NSObject<MKAnnotation> {
	CLLocationCoordinate2D coordinate;
    NSString *title;
    NSString *subtitle;
    Place *_place;
    int tag;
}
@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;

-(id)initWithCoordinate:(CLLocationCoordinate2D) coordinate;
-(id)initWithPlace:(Place*) place;

@property(nonatomic, copy) NSString *title;
@property(nonatomic, copy) NSString *subtitle;
@property(nonatomic, retain) Place *place;
@property(nonatomic, assign) int tag;

@end

PlaceMark.m

//
//  PlaceMark.m
//  Nina
//
//  Created by Ian MacKinnon on 11-08-22.
//  Copyright 2011 __MyCompanyName__. All rights reserved.
//

#import "PlaceMark.h"

@implementation PlaceMark

@synthesize coordinate;
@synthesize title;
@synthesize subtitle;
@synthesize place=_place;
@synthesize tag;

-(id)initWithCoordinate:(CLLocationCoordinate2D) c{
	coordinate=c;
	DLog(@"%f,%f",c.latitude,c.longitude);
    self.tag = 0;
	return self;
}

-(id)initWithPlace:(Place *)place{
    if(self = [super init]){
        self.title = place.name;
        self.subtitle = [place tagString];
        
        //self.subtitle = place.address;
        coordinate = place.location.coordinate;
        self.place = place;
    }
    self.tag = 0;
    return self;
}


-(void)dealloc{
    [title release];
    [subtitle release];
    [_place release];
    [super dealloc];
}

@end

SuggestedMapController.m

for (Place *place in self.places){     
  PlaceMark *placemark=[[PlaceMark alloc] initWithPlace:place];
  [self.mapView addAnnotation:placemark];
}


.....

- (MKAnnotationView *)mapView:(MKMapView *)theMapView viewForAnnotation:(id <MKAnnotation>)_annotation{
    
    if( [_annotation isKindOfClass:[PlaceMark class]] ){
        PlaceMark *annotation = _annotation;
        // try to dequeue an existing pin view first
        static NSString* annotationIdentifier = @"placeAnnotationIdentifier";
        
        MKAnnotationView* pinView = (MKAnnotationView *)        
        [self.mapView dequeueReusableAnnotationViewWithIdentifier:annotationIdentifier];
        
        if (!pinView) {            
            // if an existing pin view was not available, create one
            pinView = [[[MKAnnotationView alloc]
                        initWithAnnotation:annotation reuseIdentifier:annotationIdentifier] autorelease];
        } else {           
            pinView.annotation = annotation;            
        }
        pinView.hidden = false;
        pinView.enabled = true;
        pinView.canShowCallout = YES;
        pinView.calloutOffset = CGPointMake(-7, 0);
        pinView.centerOffset = CGPointMake(10, -20);
        
        UIButton* rightButton = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
        rightButton.tag = [placeSuperset indexOfObjectIdenticalTo:annotation.place];
        [rightButton addTarget:self action:@selector(showPlaceDetails:) 
              forControlEvents:UIControlEventTouchUpInside];
        
        pinView.rightCalloutAccessoryView = rightButton;
        if (annotation.place.bookmarked){
            if ( annotation.place.highlighted ) {
                pinView.image = [UIImage imageNamed:@"HilightMarker.png"];
            } else {
                pinView.image = [UIImage imageNamed:@"MyMarker.png"];
            }
        } else {
            pinView.image = [UIImage imageNamed:@"FriendMarker.png"];
        }
        
        if ( userFilter || tagFilter){
            annotation.tag = 0;
        }else {
            annotation.tag = 1;
        }
        
        for (Perspective *perspective in annotation.place.placemarks){
            if ( (!userFilter || [perspective.user.username isEqualToString:userFilter]) && (!tagFilter || [perspective.tags indexOfObject:tagFilter] != NSNotFound ) ){
                pinView.tag =1;
                annotation.tag =1;
                perspective.hidden = false;
            } else {
                perspective.hidden = true;
            }
        }
        
        if (annotation.tag == 1){
            annotation.place.hidden = false;
        } else {
            annotation.place.hidden = true;
        }
        
        if (annotation.tag == 1){
            return pinView;
        }
        
        if ( tagFilter || userFilter ){
            pinView.hidden = true;
            pinView.enabled = false;
        }
        pinView.tag = 0;
        annotation.tag = 0;
        return pinView;

    } else {
        return nil;
    }
}