Uso di stringWithFormat per comporre una NSString in XCODE

NSString *category = [row objectForKey:@"category"];
NSString *logonUser = [row objectForKey:@"username"];
user.text = [NSString stringWithFormat:@"In %@ by %@", category, logonUser];

ref ufficiale: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Strings/Articles/FormatStrings.html