Get New Location when App Enters Foreground - iphone

Question

I am having difficulty implementing what I think should be a pretty simple capability. I have an button that compares the user's location to another set of lat/lon coordinates and displays an alert telling the user if they are "nearby" or "far away" from the location. This works well if the app remains in the foreground.
However, if the app gets sent to the background, the locationManager stops updating the user's location. If this happens, when the user brings the app back up and presses the "compare location button", the app doesn't seem to be able to get the user's new coordinates correctly.
Adding receive location updates to the background modes seems to work, but I know this will drain battery an may be rejected by Apple.
All I really want is to be able to have the button wait for an accurate set of lat/lon coordinates before trying to calculate the distance between the user and the other set lat/lon coordinates. Here is what I have so far:
The Location Button Does This:
-(void) locationButton {
NSString *userLatitude =[(PDCAppDelegate *)[UIApplication sharedApplication].delegate
getUserLatitude];
NSString *userLongitude =[(PDCAppDelegate *)[UIApplication sharedApplication].delegate
getUserLongitude];
NSString *placeLatitude = [[NSUserDefaults standardUserDefaults]
stringForKey:#"savedLatitude"];
NSString *placeLongitude = [[NSUserDefaults standardUserDefaults]
stringForKey:#"savedLongitude"];
NSString *distanceURL = [NSString stringWithFormat:#"http://www.website.com/page.php?
lat1=%#&lon1=%#&lat2=%#&lon2=%#",userLatitude, userLongitude, placeLatitude,
placeLongitude];
NSData *distanceURLResult = [NSData dataWithContentsOfURL:[NSURL
URLWithString:distanceURL]];
NSString *distanceInFeet = [[NSString alloc] initWithData:distanceURLResult
encoding:NSUTF8StringEncoding];
if ([distanceInFeet isEqualToString:#"1"]) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"You're Near!"
message:#"" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
return;
}
if ([distanceInFeet isEqualToString:#"0"]) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"You're Far!" message:#""
delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
return;
}
}
The first few lines of the locationButton method get the userLatitude and userLongitude from my App Delegate:
- (NSString *)getUserCoordinates {
NSString *userCoordinates = [NSString stringWithFormat:#"latitude: %f longitude: %f",
locationManager.location.coordinate.latitude,
locationManager.location.coordinate.longitude];
locationManager = [[CLLocationManager alloc] init];
locationManager.distanceFilter = kCLDistanceFilterNone; // whenever we move
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters; // 100 m
[locationManager startUpdatingLocation];
return userCoordinates;
}
- (NSString *)getUserLatitude {
NSString *userLatitude = [NSString stringWithFormat:#"%f",
locationManager.location.coordinate.latitude];
return userLatitude;
}
- (NSString *)getUserLongitude {
NSString *userLongitude = [NSString stringWithFormat:#"%f",
locationManager.location.coordinate.longitude];
return userLongitude;
}