How do I acquire data from a NSNotification object? - iphone

Question

I am trying to send a location update with the new location as a notification object. When I do, I receive a "EXC_BAD_ACCESS" error when I try to access the data from the notification. If I execute "po location" I see the data, but it is unclear to me why I cannot acquire it. When setting the observer, I also tried assigning the object parameter to a member variable, but then locationUpdate is never called.
Here's my code (note that ARC is enabled):
// LocationController.h
#protocol LocationDelegateProtocol
#required
- (void)locationUpdate:(CLLocation *)location;
#end
#interface LocationController : NSObject <CLLocationManagerDelegate> {
CLLocationManager *locationManager;
id delegate;
}
#property(nonatomic, retain) CLLocationManager *locationManager;
#property(nonatomic, strong) id delegate;
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation;
+ (LocationController *)sharedInstance; // this class is a singleton
#end
// LocationController.m
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
[Notification locationChanged:newLocation];
}
// Notification.h
#interface Notification : NSObject
+ (void)locationChanged:(CLLocation *)newLocation;
#end
extern NSString *const kLocationChanged;
// Notification.m
NSString *const kLocationChanged = #"NewLocation";
[[NSNotificationCenter defaultCenter] postNotificationName:kLocationChanged object:newLocation];
// ViewController.h
#interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, LocationDelegateProtocol> {
...
}
...
- (void)locationUpdate:(CLLocation *)location;
#end
// ViewController.m
- (void)setupNotifications {
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(locationUpdate:) name:kLocationChanged object:nil];
// I've tried setting object to a member var "CLLocation *objectFromNotification", but then locationUpdate() is never called.
}
- (void)locationUpdate:(NSNotification *)notification {
CLLocation *location = (CLLocation *) [notification object];
// program receives signal "EXC_BAD_ACCESS" when executing NSLog below. I can see data inside location when I execute "po location".
NSLog(#"latitude = %#, longitude = %#",location.coordinate.latitude, location.coordinate.longitude);

Answer 1

Change the format specifier in your NSLog from %# to %f. You are trying to access float value as object!

Answer 2

NSNotifications have a dictionary with them called userInfo where you can put information you want to be sent with the notification.
I am going to fix your code kinda going backwards, so bear with me. You really haven't used the NSNotification class as it is typically (or intended to be) used.
To fix this situation, we have to do a bunch of things. The object value of an NSNotification post is the object that is posting the NSNotification, not the object you want to pass with it.
Add the CLLocation object to a dictionary, and pass it in as the userInfo dictionary. There is also no reason for this custom notification class stuff you have. So you can get rid of the Notification.h and Notification.m
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
NSString *const kLocationChanged = #"NewLocation";
NSDictionary *locationDict = [NSDictionary dictionaryWithObject:newLocation forKey:#"Location"];
[[NSNotificationCenter defaultCenter] postNotificationName:kLocationChanged object:nil userInfo:locationDict];
}
So now we are posting the location information with the notification. Next, handle it when you get the notification.
- (void)locationUpdate:(NSNotification *)notification {
CLLocation *location = [[notification userInfo] valueForKey:#"Location"];
NSLog(#"latitude = %f, longitude = %f",location.coordinate.latitude, location.coordinate.longitude);
}
Also, change your view controller header to the following:
#interface ViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, LocationDelegateProtocol> {
...
}
...
- (void)locationUpdate:(NSNotification *)notif;
#end