NSMutableArray of ClLocationCoordinate2D - iphone

Question

I'm trying to create then retrieve an array of CLLocationCoordinate2D objects, but for some reason the array is always empty.
I have:
NSMutableArray *currentlyDisplayedTowers;
CLLocationCoordinate2D new_coordinate = { currentTowerLocation.latitude, currentTowerLocation.longitude };
[currentlyDisplayedTowers addObject:[NSData dataWithBytes:&new_coordinate length:sizeof(new_coordinate)] ];
I've also tried this for adding the data:
[currentlyDisplayedTowers addObject:[NSValue value:&new_coordinate withObjCType:#encode(struct CLLocationCoordinate2D)] ];
And either way, the [currentlyDisplayedTowers count] always returns zero. Any ideas what might be going wrong?
Thanks!

Answer 1

To stay in object land, you could create instances of CLLocation and add those to the mutable array.
CLLocation *towerLocation = [[CLLocation alloc] initWithLatitude:lat longitude:lon];
[currentDisplayedTowers addObject:towerLocation];
To get the CLLocationCoordinate struct back from CLLocation, call coordinate on the object.
CLLocationCoordinate2D coord = [[currentDisplayedTowers lastObject] coordinate];

Answer 2

As SB said, make sure your array is allocated and initialized.
You’ll also probably want to use NSValue wrapping as in your second code snippet. Then decoding is as simple as:
NSValue *wrappedCoordinates = [currentlyDisplayedTowers lastObject]; // or whatever object you wish to grab
CLLocationCoordinate2D coordinates;
[wrappedCoordinates getValue:&coordinates];

Answer 3

You need to allocate your array.
NSMutableArray* currentlyDisplayedTowers = [[NSMutableArray alloc] init];
Then you can use it. Be sure to call release when you are done with it or use another factory method.

Answer 4

I had currentlyDisplayedTowers = nil which was causing all the problems. Also, the previous advice to init and alloc were necessary. Thanks everyone for the help!

Answer 5

For anyone else with this issue, there's another solution if you are planning on using MapKit.
(The reason I say IF, of course, is because importing a module such as MapKit purely for a convenient wrapper method is probably not the best move.. but nonetheless here you go.)
#import MapKit;
Then just use MapKit's coordinate value wrapper whenever you need to:
[coordinateArray addObject:[NSValue valueWithMKCoordinate:coordinateToAdd]];
In your example..
[currentlyDisplayedTowers addObject:[NSValue valueWithMKCoordinate:new_coordinate]];