What is self in ObjC? When should i use it?

Question

What does self mean in Objective-C? When and where should I use it? Is it similar to this in Java?

Answer 1

Two important notes:

1. The class itself, e.g. UIView (I'm NOT talking about a UIView object) is itself an object, and there is a self associated with it. So for example, you can reference self in a class method like this:

   // This works
   +(void) showYourself { [self performSelector: @selector(makeTheMostOfYourself)]; }
   
   // Class method!
   +(void) makeTheMostOfYourself { }
   

2. Note that the compiler does NOT raise any warnings or errors, even if the self you mean to reference is an object and not a class. It is VERY easy to cause crashes this way, for example:

   // This will crash!
   +(void) showYourself { [self performSelector: @selector(makeTheMostOfYourself)]; }
   
   // Object method!
   -(void) makeTheMostOfYourself { }
   
   
   
   // This will crash too!
   -(void) showYourself2 { [self performSelector: @selector(makeTheMostOfYourself2)]; }
   
   // Class method!
   +(void) makeTheMostOfYourself2 { }
   

   Sadly, this makes class methods a bit harder to use, which is unfortunate because they are a valuable tool for encapsulation through information hiding. Just be careful.