Objective C: How to resolve 'unrecognized selector sent to instance' error

Question

I am trying to access a property of instance object using the following code

for (User *user in likersArray) 
{
    //Set variables for dictionary
    NSString *nameLength = [NSString stringWithFormat:@"%i",[user.nickname length]];
}

However, I keep getting the following error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString nickname]: unrecognized selector sent to instance 0x8c0f780'

My user class is defined as below

@interface User : NSObject <NSCoding>
{
NSString *uid;
NSString *name;
NSString *nickname;
}

@property (nonatomic, copy) NSString *uid;
@property (nonatomic, copy) NSString *name;
@property (nonatomic, copy) NSString *nickname;

@end

Answer 1

That error means that not everything in your likersArray is a User object. At least one thing in there is an NSString.