Question

I have derived from a 3rd party class, and when I attempt to call a method in the base class, I get the x may not respond to y compiler warning.

How can I remove the warning?

Repro:

@interface ThirdPartyBaseClass : NSObject {}
+(id)build;
-(void)doStuff;
@end

@implementation ThirdPartyBaseClass
+(id) build{
    return [[[self alloc] init] autorelease];
}
-(void)doStuff{ 
}
@end

@interface MyDerivedClass : ThirdPartyBaseClass {}
+(id)buildMySelf;
@end

@implementation MyDerivedClass
+(id)buildMySelf{
    self = [ThirdPartyBaseClass build];
    [self doStuff]; // compiler warning here - 'MyDerivedClass' may not respond to '+doStuff'
return self;
}
@end

Thanks!

Answer 1

In a class method (preceded by the ‘+’), ‘self’ is not an instance of the class; ‘self’ is the Class object, which only responds to Class methods, not instance methods. If you’re building an instance so you can call doStuff on it and return it, you’ll need to use a separate variable:

+ (id) buildMySelf
{
   MyDerivedClass *myDerivedClassInstance;

   myDerivedClassInstance = [self build];
   [myDerivedClassInstance doStuff];

   return myDerivedClassInstance;
}