ClLocationCoordinate2D的NSMutableArray

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]];