Getting Latitude and Longitude Values Using Geocoder

Question

I write the below code for getting Latitude and Longitude Values from an Address.I am having 2 Address fields From and To.

-(void)getLatLong:(NSString *)string
{
CLGeocoder *geocoder = [[CLGeocoder alloc] init];

[geocoder geocodeAddressString:string completionHandler:^(NSArray *placemarks, NSError *error) {
    if([placemarks count]) {
        CLPlacemark *placemark = [placemarks objectAtIndex:0];
        CLLocation *location = placemark.location;
        CLLocationCoordinate2D coordinate = location.coordinate;
        NSLog(@"coordinate = (%f, %f)", coordinate.latitude, coordinate.longitude);
        if([string isEqualToString:self.from.text])
        {
            fromLat = coordinate.latitude;
            fromLng = coordinate.longitude;

        }
        else if([string  isEqualToString:self.to.text])
        {
            toLat = coordinate.latitude;
            toLng = coordinate.longitude;
        }
    }
}];
}  
- (void)display
{
    NSLog(@"%f",fromLat);
    NSLog(@"%f",fromLng);
    NSLog(@"%f",toLat);
    NSLog(@"%f",toLng);
}
- (IBAction)getLatLongs:(id)sender
{
    [self getLatLong:self.from.text];
    [self getLatLong:self.to.text];
    [self display];
}

After Clicking the Submit button for First time the output is:

 2014-03-20 10:15:28.178 Application[746:70b] 0.000000  
 2014-03-20 10:15:28.179 Application[746:70b] 0.000000  
 2014-03-20 10:15:28.180 Application[746:70b] 0.000000  
 2014-03-20 10:15:28.181 Application[746:70b] 0.000000   
 2014-03-20 10:15:29.019 Application[746:70b] coordinate = (17.387337, 78.480835)  
 2014-03-20 10:15:29.134 Application[746:70b] coordinate = (16.516667, 80.616667) 

After Clicking the Submit button for Second time the output is:

 2014-03-20 10:15:28.178 Application[746:70b] 17.387337  
 2014-03-20 10:15:28.179 Application[746:70b] 78.480835 
 2014-03-20 10:15:28.180 Application[746:70b] 16.516667  
 2014-03-20 10:15:28.181 Application[746:70b] 80.616667  
 2014-03-20 10:15:29.019 Application[746:70b] coordinate = (17.387337, 78.480835)  
 2014-03-20 10:15:29.134 Application[746:70b] coordinate = (16.516667, 80.616667) 

I want to Know Why it is Getting All Zero's for First time if i call display method after Getting LaltLong Method.

Answer 1

when you call [self getLatLong:self.from.text];

It calls [geocoder geocodeAddressString:string completionHandler:^{}]; which is GCD. Which runs on different thread.

Then you instantly calls [self display]; till then values are not received in GCD. thats why you are getting 0 first time. Next time when you call [self display]; values are already present so it prints as it is.

Use breakpoints in -(void)display and inside GCD to get more idea.

try to call [self display]; inside GCD.

-(void)getLatLong:(NSString *)string
{
    CLGeocoder *geocoder = [[CLGeocoder alloc] init];

    [geocoder geocodeAddressString:string completionHandler:^(NSArray *placemarks, NSError *error) {
    if([placemarks count]) {
        CLPlacemark *placemark = [placemarks objectAtIndex:0];
        CLLocation *location = placemark.location;
        CLLocationCoordinate2D coordinate = location.coordinate;
        NSLog(@"coordinate = (%f, %f)", coordinate.latitude, coordinate.longitude);
        if([string isEqualToString:self.from.text])
        {
            fromLat = coordinate.latitude;
            fromLng = coordinate.longitude;
            [self display];
        }
        else if([string  isEqualToString:self.to.text])
        {
            toLat = coordinate.latitude;
            toLng = coordinate.longitude;
            [self display];
        }
    }
    }];
} 

- (void)display
{
   NSLog(@"%f",fromLat);
   NSLog(@"%f",fromLng);
   NSLog(@"%f",toLat);
   NSLog(@"%f",toLng);
}

- (IBAction)getLatLongs:(id)sender
{
   [self getLatLong:self.from.text];
   [self getLatLong:self.to.text];
}

Answer 2

i Solved My Problem Like This It's Working Fine

-(void)getLatLong:(NSString *)string
{
CLGeocoder *geocoder = [[CLGeocoder alloc] init];

[geocoder geocodeAddressString:string completionHandler:^(NSArray *placemarks, NSError *error) {
if([placemarks count]) {
    CLPlacemark *placemark = [placemarks objectAtIndex:0];
    CLLocation *location = placemark.location;
    CLLocationCoordinate2D coordinate = location.coordinate;
    NSLog(@"coordinate = (%f, %f)", coordinate.latitude, coordinate.longitude);
    if([string isEqualToString:self.from.text])
    {
        fromLat = coordinate.latitude;
        fromLng = coordinate.longitude;

    }
    else if([string  isEqualToString:self.to.text])
    {
        toLat = coordinate.latitude;
        toLng = coordinate.longitude;
    }
}
}];
}  
- (void)display
{
 NSLog(@"%f",fromLat);
 NSLog(@"%f",fromLng);
 NSLog(@"%f",toLat);
 NSLog(@"%f",toLng);
}
- (IBAction)getLatLongs:(id)sender
{
 [self getLatLong:self.from.text];
 [self getLatLong:self.to.text];
  int64_t delayInSeconds = 1.5;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

       [self display];
    });
}

}