Ensure locationManager has finished then perform request - ios

Question

I am using CoreLocation to grab the users location. I need to grab the users location then send that to the server. I have it all working, but! I am implementing locationManager:(CCLLocationManager *)manager...
My url request is hitting before the location is found. Whats the best way to:
Request location
Store in string
Send string to request
I want to ensure the location is found before its sent. Do I check against the instance of the class with a conditional and inside the block hit the server. I dont need to keep updating, just grab once and stopUpdatingLocation
Was going through this post previously: Getting Longitude/Latitude of the User When the viewDidLoad
What I have so far:
- (void)viewDidLoad {
[super viewDidLoad];
locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyThreeKilometers;
[locationManager startUpdatingLocation];
...more below... server request below here
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
NSLog(#"didUpdateToLocation: %#", newLocation);
CLLocation *currentLocation = newLocation;
if (currentLocation != nil) {
NSLog(#"found!");
[locationManager stopUpdatingLocation];
}
}
Thoughts on how to do that? I think the conditional may work, but not sure if there was a proper way to handle that using the methods provided from CoreLocation.

Answer 1

Create a new method that will perform your location-dependent code. Then once you have the location (I.e. After the NSLog(#"found!"); line), call this method.
Note that the method may get called multiple times as the location accuracy improves - you might want to handle this.
For example:
- (void)viewDidLoad {
[super viewDidLoad];
locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyThreeKilometers;
[locationManager startUpdatingLocation];
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
NSLog(#"didUpdateToLocation: %#", newLocation);
CLLocation *currentLocation = newLocation;
if (currentLocation != nil)
{
NSLog(#"found!");
[self handleLocation:newLocation];
[locationManager stopUpdatingLocation];
}
}
- (void)handleLocation:(CLLocation*)location
{
// handling code here
}

Answer 2

The location manager is asynchronous. You have to ask for location updates, then wait for it to call you back.
Worse, the first several updates are usually garbage that needs to be thrown away.
The first location update frequently has a timestamp that is hours, days, or even weeks old. You first have to check to make sure the timestamp is in the last few seconds.
Once you've done that, you need to check the horizontal accuracy, and make sure the reading is accurate enough. Often when you first start the location manager the first few readings have an accuracy value of more than a kilometer, which is awful. (Accuracy is really a radius value. You can only be sure that the location you get is somewhere inside a circle with the specified radius.) You need to come up with an app-specific accuracy reading that is "good enough", and throw away accuracy readings until you get one that is good enough. You also need to check for negative accuracy readings, which mean that the GPS is returning invalid values.
Next, you have to allow for the case where the GPS doesn't settle down in a reasonable time. (Sometimes it can take multiple minutes, or simply fail to get a good reading.) In that case you need to handle it as a failure.
So, to handle all that you need to write your locationManager:didUpdateLocation: method to check the time stamp and the horizontal accuracy to make sure the reading is actually good. You also need to make sure you time out and report a failure if you can't get a decent location reading after a reasonable wait. One way to do this is to start a "give up" timer when you first begin location updates, and after you get a good reading, kill it. If the timer fires, stop location updates and report a "can't get a good location reading" error to your user. Understand that it's not uncommon to take 10 or 15 seconds to get a decent accuracy reading.