Unrecognized selector sent to instance

Question

I'm having trouble with this method, more specifically I'm having trouble with my logic. I'm trying to combine two array's firstName and lastName both sequentially matching up. I was thinking I could us a for loop to iterate through the array count and then combine the array's using arrayByAddingObjectsFromArray.

Unfortunately it seems that this part throws up an error : __NSCFConstantString arrayByAddingObjectsFromArray:]: unrecognized selector sent to instance 0x10c824218

Any ideas why this is? What does it mean by selector; is that it doesn't like the array i'm trying to pass to it?

- (NSString *)badgeForSpeaker:(NSString *)speaker{ NSArray *firstName = @[@"Adele", @"Edsger", @"Joan", @"Clarence", @"Margaret", @"George", @"Tim", @"Jean"]; NSArray *lastName = @[@"Goldberg",@"Dijkstra",@"Clarke",@"Ellis",@"Hamilton",@"Boole",@"Berners-Lee",@"Bartik"]; NSString *uppercaseString = [speaker copy]; NSMutableString *hello = [[NSMutableString alloc]init]; for (NSUInteger i =0; i < [lastName count] ; i++) { uppercaseString = [lastName[i] capitalizedString]; hello = [@"Hello, my name is " mutableCopy]; firstName = [firstName[i] arrayByAddingObjectsFromArray:lastName[i]]; NSString *fullNameString = [firstName componentsJoinedByString:@" "]; [hello appendFormat:@"%@",fullNameString]; NSLog(@"%@",hello); } return hello; }

firstName[i] returns NSString object. the method arrayByAddingObjectsFromArray belongs to NSArray — ProblemSlover
– ProblemSlover, Commented Oct 22, 2015 at 17:07
My fault, I expect "hello" to return a String "Hello, my name is [firstName] [lastName]." — Diego Aguirre
– Diego Aguirre, Commented Oct 22, 2015 at 17:42
Possible duplicate of How can I debug 'unrecognized selector sent to instance' error — Cœur
– Cœur, Commented Jul 8, 2019 at 5:54

luckyShubhra · Accepted Answer · 2015-10-22 17:44:43Z

You are getting this error as arrayByAddingObjectsFromArray method is not defined for NSString object. You are trying to use this method with a NSSting object as first name[i] returns a NSString not an NSArray.

Why r u complicating things you can achieve the same by

NSArray *firstName = @[@"Adele", @"Edsger", @"Joan", @"Clarence", @"Margaret", @"George", @"Tim", @"Jean"]; NSArray *lastName = @[@"Goldberg",@"Dijkstra",@"Clarke",@"Ellis",@"Hamilton",@"Boole",@"Berners-Lee",@"Bartik"]; NSMutableArray *array = [[NSMutableArray alloc] init]; NSString *hello; for (NSUInteger i = 0; i < [lastName count] ; i++) { NSString *fullName = [[[firstName objectAtIndex:i] uppercaseString]stringByAppendingString:[@" " stringByAppendingString:[[lastName objectAtIndex:i]uppercaseString]]]; [array addObject:fullName]; hello = [NSString stringWithFormat:@"Hello, my name is %@", fullName]; NSLog(@"%@",hello); }

Hope it helps.. Happy Coding.. :)

Ty Lertwichaiworawit · Accepted Answer · 2015-10-22 17:34:52Z

If I undestand correctly, you want the hello string to be

Hello, my name is Firstname Lastname

You can do this by:

NSArray *firstName = @[@"Adele", @"Edsger", @"Joan", @"Clarence", @"Margaret", @"George", @"Tim", @"Jean"]; NSArray *lastName = @[@"Goldberg",@"Dijkstra",@"Clarke",@"Ellis",@"Hamilton",@"Boole",@"Berners-Lee",@"Bartik"]; NSMutableArray *fullNameArray = [[NSMutableArray alloc] init]; NSString *hello; NSString *uppercaseString = [speaker copy]; for (NSUInteger i = 0; i < [lastName count] ; i++) { uppercaseString = [lastName[i] capitalizedString]; //join firstName and lastName in a string NSString *fullName = [[firstName objectAtIndex:i] stringByAppendingString:[NSString stringWithFormat:@" %@", uppercaseString]]; //add fullName string to fullNameArray [fullNameArray addObject:fullName]; //set it in hello string hello = [NSString stringWithFormat:@"Hello, my name is %@", fullName]; NSLog(@"%@",hello); }

Thanks tnylee, this definitely closer matches my original code and logic. Appreciate the help

Anton Onizhuk · Accepted Answer · 2015-10-22 17:58:51Z

Method arrayByAddingObjectsFromArray: is used to connect two arrays. It works like this:

NSArray * first = @[@1, @2, @3]; //[1, 2, 3] NSArray * second = @[@4, @5]; //[4, 5] NSArray * bothArrays = [first arrayByAddingObjectsFromArray:second]; // [1, 2, 3, 4, 5]

If you really wanna use this method for this task, you can wrap strings into arrays, like this:

NSArray * fullNameComponents = [@[firstName[i]] arrayByAddingObjectsFromArray:@[lastName[i]]];

but it is like the most unefficient whay to do that. Much better is to create array instantly:

NSArray * fullNameComponents = @[firstName[i], secondName[i]];

In your case the best option will be to omit all the array job, and create your string using format:

NSString * hello = [NSString stringWithFormat:@"Hello, my name is %@ %@", firstName[i], secondName[i]];

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