redundant calculations slowing down UITableView - ios

Question

I am creating a scrollable UITableView in which each cell requires to make a call to the Google Directions Matrix API.For some reason,each time I scroll it makes the call and does the calculations separately which significantly takes a toll on the responsiveness of the scrolling.Here's the code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
if(tableView.tag == 1) {
return [self specialTableViewCell: tableView];
}
static NSString *CellIdentifier = #"OfferCell";
OTNOfferCell *cell = (OTNOfferCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
{
// create cell using style Subtitle
cell = [[OTNOfferCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier];
}
PFObject *venue = [self.venues objectAtIndex:indexPath.section];
cell.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"MainPage Item.png"]];
cell.selectedBackgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"MainPageItemSelected.png"]];
cell.clubNameLabel.text = [venue valueForKey: #"name"] ;
PFFile *photo = [venue objectForKey:#"logo"];
NSData *data = [photo getData];
UIImage *image = [UIImage imageWithData: data];
cell.clubLogoImageView.image = image;
int count = [[venue valueForKey:#"events"] count];
if(count == 1)
{
cell.numberOfEventsLabel.text = #"1 Event";
}
else
{
cell.numberOfEventsLabel.text = [NSString stringWithFormat:#"%d Events", count];
}
PFGeoPoint *destinationLocation = [venue objectForKey:#"geopoint"];
locationManager = [[CLLocationManager alloc] init];
locationManager.distanceFilter = kCLDistanceFilterNone;
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
[locationManager startUpdatingLocation];
PFGeoPoint *currentLocation = [PFGeoPoint geoPointWithLatitude:locationManager.location.coordinate.latitude longitude:locationManager.location.coordinate.longitude];
NSString *current = [venue objectForKey:#"address"];
NSLog(#"%#",current);
NSString *urlString = [NSString stringWithFormat:#"http://maps.googleapis.com/maps/api/distancematrix/json?origins=%#&destinations=San+Francisco&mode=driving&language=en&sensor=true&units=imperial",current];
NSURL *url = [NSURL
URLWithString:[urlString
stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
NSData *googledata = [NSData dataWithContentsOfURL:url];
NSError *error;
NSMutableDictionary *json = [NSJSONSerialization JSONObjectWithData:googledata options:kNilOptions error:&error];
NSString *result = [[[[[[json objectForKey:#"rows"] objectAtIndex: 0] objectForKey:#"elements"] objectAtIndex:0]objectForKey:#"distance"]objectForKey:#"text"];
double tempd = [currentLocation distanceInMilesTo:destinationLocation];
NSString *distance = [NSString stringWithFormat:#"%f",tempd];
NSString *distanceTrunc = [distance substringToIndex: MIN(3, [distance length])];
cell.distanceLabel.text = [NSString stringWithFormat:#"%# mi", distanceTrunc];
return cell;
}
Is there any way to fix this,wherein the calculation is done only once.

Answer 1

You should not be making these calculations in the cell. UITableViewCells are part of the view layer.
You should make the requests in your controller and store the results in something like an NSArray. Then cellForRowAtIndexPath should just pull data from that array.