如何跟踪用户的位置刚好足以抓住位置？

Question

I have three points, but really only the first one is the most important

• In order to preserve battery life, I'm trying to have the locationManager turn on just long enough to get the user's location and then shut off. What is the best means to do so?

• I don't always need to know the user's location, but having a relatively accurate location when the user hits search is important (within perhaps a couple dozen city blocks, 10,000 meters, maybe even less accurate).

• I'm sending a request to a server and then getting the results, and after THAT delay, I need a more accurate version of the user location (within 100 meters is fine).

I don't know how much of this is too nitpicky, but if the last two points are possible/efficient battery-wise, then please let me know how to do it!

Answer 1

You can easily stop tracking location when your CLLocationManager 's delegate receives a location update meeting your desired accuracy.

To start updating location, do something like:

CLLocationManager *locationManager = [CLLocationManager alloc] init];
locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
[locationManager startUpdatingLocation];

Then implement the appropriate CLLocationManagerDelegate method:

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
  CLLocation *foundLocation = [locations lastObject];
  if (foundLocation && foundLocation.horizontalAccuracy < kYourDesiredAccuracyInMetres)
  {
    [manager stopUpdatingLocation];
    //Do whatever else with the location you've established
  }
}

You should be able to tweak this meet your requirements, by checking the accuracy of the returned locations returned and either stopping the updates or letting them continue (if you need better accuracy).

It's also a good idea to set a timer when you start updating location, and stop updates if you haven't found a location within a set amount of time. You should also implement the locationManager:didFailWithError: delegate method to check whether you can access location services at all.

Answer 2

LocationManager could be stopped after location information of user has been retrieved .

CLLocationManager* locationManager = [ [ CLLocationManager alloc] init];

locationManager.delegate = self; //we must implement the protocol

locationManager.distanceFilter = kCLDistanceFilterNone;
locationManager.headingFilter = kCLHeadingFilterNone;
locationManager.desiredAccuracy = kCLLocationAccuracyThreeKilometers; 


//To turn on gps (if it isn't on already)
[locationManager startUpdatingLocation];

//To turn gps off (if no other apps are listening)
[locationManager stopUpdatingLocation];