Reading JSON from URL and adding MKAnnotations - iphone

Question

I've been through several different tutorials trying to get this working, but they seem to gloss over some crucial steps that a beginner might not know.
I have a JSON file at a URL with name, latitude, and longitude listed. How can I import that to an array or dictionary (I don't know the difference), and then iterate over it and create a new annotation with each iteration.
IOS6, Storyboards
_ Added Code _
ViewController.h
#import <UIKit/UIKit.h>
#import <MapKit/MapKit.h>
#interface ViewController : UIViewController {}
#property (weak, nonatomic) IBOutlet MKMapView *mapView;
#property (nonatomic, strong) NSMutableData *downloadData;
#end
ViewController.m
#import "ViewController.h"
#import "MapViewAnnotation.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
_downloadData = [NSMutableData new];
NSURL *requestURL = [NSURL URLWithString:#"OMITTED/apptest/locations.json"];
NSURLRequest *request = [NSURLRequest requestWithURL:requestURL];
NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:self];
[connection start];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[_downloadData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
id parsed = [NSJSONSerialization JSONObjectWithData:_downloadData options:kNilOptions error:nil];
for (NSDictionary *pointInfo in parsed)
{
NSLog([parsed objectForKey:#"name"]);
double xCoord = [(NSNumber*)[parsed objectForKey:#"lat"] doubleValue];
double yCoord = [(NSNumber*)[parsed objectForKey:#"lon"] doubleValue];
CLLocationCoordinate2D coords = CLLocationCoordinate2DMake(xCoord, yCoord);
MKPointAnnotation *point = [MKPointAnnotation new];
point.coordinate = coords;
point.title = [parsed objectForKey:#"name"];
[self.mapView addAnnotation:point]; // or whatever your map view's variable name is
}
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(void)viewDidUnload {
[super viewDidUnload];
// ARC Problem --- [_mapView release];
self.mapView = nil;
}
#end

Answer 1

With iOS 5 there's a JSONSerializer class that can convert the raw JSON data from your URL into an array or dictionary as appropriate.
You'll need to download the data from the server:
NSURL *requestURL = [NSURL URLWithString:#"<your url here>"];
NSURLRequest *request = [NSURLRequest requestWithURL:requestURL];
NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:self];
[connection start];
Then you'll add these delegate methods:
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[_downloadData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
id parsed = [NSJSONSerialization JSONObjectWithData:_downloadData options:kNilOptions error:nil];
}
_downloadData is an instance variable or property of your class of type NSMutableData.
That parsed variable will contain your data from the server. It's probably an array if it's a list of points, so you can iterate through it using fast enumeration:
for (NSDictionary *pointInfo in parsed) {
double xCoord = [(NSNumber*)[parsed objectForKey:#"<key for lat coord>"] doubleValue];
double yCoord = [(NSNumber*)[parsed objectForKey:#"<key for long coord>"] doubleValue];
CLLocationCoordinate2D coords = CLLocationCoordinate2DMake(xCoord, yCoord);
MKPointAnnotation *point = [[MKPointAnnotation new] autorelease];
point.coordinate = coords;
point.title = [parsed objectForKey:#"<key for title>"];
[self.mapView addAnnotation:point]; // or whatever your map view's variable name is
}

Answer 2

I have an open source project on GitHub that uses the serializer with the NSCoding protocol so you can automatically create instances right from the JSON stream.
It's here.