IOS: NSKnownKeysDictionary1 error - ios

Question

I have an object selectedActivity defined as follows:
#property (strong, nonatomic) Activities *selectedActivity;
At the point I need to work with it logs out as:
{
actname = "Running";
aid = 23;
}
The Activities object is an NSManaged object and its .h file looks like this.
#interface Activities : NSManagedObject
#property (nonatomic, retain) NSString * actname;
#property (nonatomic, retain) NSNumber * aid;
#end
I am trying to place one of the object properties in a variable to work with it using the following:
NSNumber *aid = _selectedActivity.aid;
However, the above line gives the following error message:
[NSKnownKeysDictionary1 aid]: unrecognized selector sent to instance 0x147842fb0
Can anyone explain this error and how to fix it?
Thanks for any suggestions.
Update:
setting of selected activity
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
_selectedActivity =([_activities objectAtIndex:row]);
NSLog(#"selectedActivity in pickerview%#",_selectedActivity);
}
//activities in .h file
#property (strong, nonatomic) NSArray *activities;
//setting of activities
self.activities= [self getActivities];
//method that gets activities
- (id) getActivities{
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Activities"];
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:#"created" ascending:NO];
[fetchRequest setSortDescriptors:#[sort]];
NSError *error = nil;
self.managedObjectContext = [Model sharedInstance].managedObjectContext;
NSArray *results = [self.managedObjectContext executeFetchRequest:fetchRequest
error:&error];
NSMutableArray *mutableresults = [results mutableCopy];
[mutableresults removeObjectIdenticalTo:[NSNull null]];
return mutableresults;
}

Answer 1

The results are coming as a dictionary.
instead of the usual NSManagedObject-style value retrieval:
Objective-C
NSString *actname = _selectedActivity.actname;
NSNumber *aid = _selectedActivity.aid;
Swift
let actname:String = _selectedActivity.actname
let aid:Int = _selectedActivity.aid
Use the NSDictionary-style value retrieval, like so:
Objective-C:
NSString *actname = [_selectedActivity valueForKey:#"actname"];
NSNumber *aid = [[_selectedActivity valueForKey:#"aid"] intValue];
Swift (tested as of 3.0.1)
_selectedActivity(forKey: "actname") as! String
_selectedActivity.value(forKey: "aid") as! Int