CODEWITHSUNDEEP
iosobjective-ccllocationmanager
MichiZH
MichiZH

Reputation: 5807

iOS: When I try to get CLLocation by click, there is most of the time a "big" lag

I'm first using the CoreLocation framework. I have a table and by button click a new location should be added and the distance to all entries in the table should be shown and updated all the time. That is why I have a BOOL saveNewLocation which is set to Yes when the button is clicked. Because the updates need to happen still all the time in the background, but when the button is clicked only a new entry is added.

At the moment I have this in my viewDidLoad:

self.locationManager = [[CLLocationManager alloc] init];
    self.locationManager.delegate = self;
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
    // Check for iOS 8. Without this guard the code will crash with "unknown selector" on iOS 7.
    if ([self.locationManager respondsToSelector:@selector(requestWhenInUseAuthorization)]) {
        [self.locationManager requestWhenInUseAuthorization];
    }
    [self.locationManager startUpdatingLocation];

And this is my delegate method:

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    self.currentLocation = newLocation;
    if(self.saveNewLocation){
       [PointOfInterest addPointOfInterest:newLocation withAddress:@"" andNotes:@"" inManagedObjectContext:self.cdh.context];
        self.saveNewLocation = NO;
    }
    [self updateAllDistances];
}

And this my button:

- (IBAction)addLocationClicked:(id)sender {
    self.saveNewLocation = YES;
}

But the problem at the moment is that when you click this button, there is sometimes a big lag and nothing happens. Sometimes immediately a new location is added. How can I avoid this lag and instantly add a new location by click?

Upvotes: 0

Views: 97

Answers (1)

Aaron Hayman
Aaron Hayman

Reputation: 8502

The time interval between update calls to the location manager delegate is variable, so the behavior you're experiencing is expected.

CLLocationManager has a property called location which returns the last known location of the user (or nil if you've never used the Location Manager in the app).

Instead of waiting for the LocationManager to update, grab the last known location of the user instead:

- (IBAction)addLocationClicked:(id)sender {
    CLLocation *location = self.locationManager.location;
    if (location && [NSDate timeIntervalSinceReferenceDate] - location.timeStamp.timeIntervalSinceReferenceDate < 60 * 10){
    //Do something with the location if the location manager returns a location within the last 10 minutes
    } else {
       self.saveNewLocation = YES;
    }
}

If the app has never asked for it's location, you may get nil, in which case you'll have to wait for the locationManager to update. But otherwise, you can just grab the last known location. You can also check whether the location was update recently by checking the timeStamp on the location object.

You also may want to set a state flag indicating that the app should wait for a location update when the location manager is first used. When you first start up the LocationManager, you can't really know how up-to-date that location is. But once the manager begins updating the delegate, you can be reasonably certain the location manager holds a fairly up-to-date location.

Upvotes: 2

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