Give a time between tasks - iOS - ios

Question

I'm getting my location position from the iPhone's GPS. I want to get the coordinate from the same point 15 times (to get the best horizontal accuracy).
Is there a way to wait for example, 2 seconds between one coordinate and another?
I use an object called coordinate, with latitude and longitude as property.
.... Exemple code
Coordinate * coord = [[Coordinate alloc] init];
NSMutableArray *coordinates = [[NSMutableArray alloc] init];
for (i=0 ; i<=14; i++)
{
coord = newlocation;
[coordinates addObject:coord];
.... some code to wait 2 seconds before add a new object to the array....
}
I tried to use NSThread sleepfortimeinterval, but the view freezes.
Thanks

Answer 1

Rather than having a for loop like this, you could theoretically use a repeating NSTimer that fired every two seconds, and then invalidate the timer after 15 iterations.
But I'd not suggest doing that, but rather shift to an event-driven model, waiting for calls to your didUpdateLocations. There's no point in checking in two seconds, if didUpdateLocations hasn't been updated. Likewise, there's no point in repeatedly checking 15 times over 30 seconds if, for example, you get a really accurate location after 5 seconds.
I'd suggest start monitoring the location, watch the locations as they come in with subsequent calls to didUpdateLocations, and examine horizontalAccuracy of the CLLocation (which tells you how accurate the location is). Once you reach the desired horizontalAccuracy, you can declare success (e.g. stop monitoring locations or whatever). You could also establish a NSTimer that automatically turned off the monitoring of locations after 30 seconds, if you want, as well.
For example:
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"%s", __PRETTY_FUNCTION__);
[self startStandardUpdates];
// after 30 seconds, if we haven't found a location, declare success with whatever we got (if anything)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(30.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self stopStandardUpdates]; // stop monitoring location if you want
if (!self.foundLocation) {
if (self.bestLocation) {
NSLog(#"Didn't find perfect location, but location has accuracy of %.1f meters", self.bestLocation.horizontalAccuracy);
} else {
NSLog(#"Even after 30 seconds, did not find any locations!");
}
}
});
}
#pragma mark - Location Services
- (void)startStandardUpdates
{
// Create the location manager if this object does not
// already have one.
if (nil == self.locationManager)
self.locationManager = [[CLLocationManager alloc] init];
self.locationManager.delegate = self;
self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
// Set a movement threshold for new events.
self.locationManager.distanceFilter = 5;
[self.locationManager startUpdatingLocation];
}
- (void)stopStandardUpdates
{
[self.locationManager stopUpdatingLocation];
self.locationManager = nil;
}
#pragma mark - CLLocationManagerDelegate
- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
CLLocation* location = [locations lastObject];
NSLog(#"%s: horizontalAccuracy = %.1f", __FUNCTION__, location.horizontalAccuracy);
if (location.horizontalAccuracy < 0) // not a valid location
return;
// this checks to see if the location is more accurate than the last;
// or you might just want to eliminate this `if` clause, because if
// you get updated location, you can probably assume it's better than
// the last one (esp if the user might be moving)
if (!self.bestLocation || location.horizontalAccuracy <= self.bestLocation.horizontalAccuracy) {
self.bestLocation = location;
}
if (location.horizontalAccuracy <= 5) { // use whatever you want here
NSLog(#"Found location %#", location);
self.foundLocation = YES;
[self stopStandardUpdates]; // stop it if you want
}
}
This uses the following properties:
#property (nonatomic, strong) CLLocationManager *locationManager;
#property (nonatomic, strong) CLLocation *bestLocation;
#property (nonatomic) BOOL foundLocation;