Call instance method from class method

Question

So I need to call some instance methods from class methods in Objective-C...

Example :

+(id)barWithFoo:(NSFoo *) {
[self foo]; //Raises compiler warn         


        

Answer 1

If you want to call an instance method you need an instance to call the method on.

self is a reference to the instance that is being messaged. Thus self in a class method is the class and self in an instance method is an instance of the class.

So, naively, you might do:

+(id)barWithFoo:(NSFoo *) {
    [[[self alloc] init] foo]; //Raises compiler warning. 
}

-(void)foo {
//cool stuff
}

Of course, that'd leak memory in a non-GC application (since the instance isn't being released or autoreleased). Instead of explaining why, I will point you to the Objective-C intro documentation. It is some awesome stuff, covering both Objective-C and general object oriented programming patterns.