Question

I will try to make myself as clear as possible. Let start from the beginning. I have an application with a tableview that contains a list of places with distances from myLocation. Now everytime I get an update in the gps location I run the following code

- (void)locationUpdate:(CLLocation *)location {
 myLocation = location;
 for (Trek * trek in list) {
  CLLocation *loc = [[CLLocation alloc] initWithLatitude:[trek latitude_start]             longitude:[trek longitude_start]];
  double dis = [locationManager getDistance: loc];
  [trek setDistance:dis];
  [trek setDistanceUnit];
  [loc release];
 }

 [self.tableView reloadData];
}

Now this piece of code [trek setDistanceUnit]; calls

-(void) setDistanceUnit {

 if (self.distance < 1000.0) 
  self.distanceString = [NSString stringWithFormat:@"%.0lf m", self.distance];
}

Now if I use only distanceString the application crash. Now I think it may have something to do with the fact that those updates may run concurrently (in parallel) to the access required by the view to draw the cells. Anyone has any idea? I can post more code if helpful, I just didn’t want to post too much to make this post too long.

I tried to search everywhere but I could not found anything so far.

Thanks in advance,
Umberto

PS Now the application is working but I would like to understand what is going on.

Answer 1

If your distanceString is a retain property, assigning it without self sets it up for a crash because you bypass the setter, and assign the string without retaining it. So when the string gets deallocated on being sent to the autorelease pool, your app crashes.

By synthesizing the accessors using @synthesize and using the dot notation (or setDistanceString:), the object will retain the string for you so that it always has a pointer to it for itself (until it’s released).