Question

I have a class that has this in the initializer:

@implementation BaseFooClass

-(id) init
{
     if (self = [super init])
     {
          // initialize instance variables that always need to start with this value
     }

     return self;
}

-(id) initWithSomeInt:(int) someInt
{
     if (self = [self init]) // <-- I need to make sure that I am calling BaseFooClass's init here, not SubFooClass's, does that make sense?
     {
          self.someInt = someInt;
     }

     return self;
}

@end

That is all fine and dandy. My problem is that when I implement the subclass:

@implementation SubFooClass

-(id) init
{
     return [self initWithSomeInt:0];
}

-(id) initWithSomeInt:(int) someInt
{

     if (self = [super init]) // <--- Infinite loop (stack overflow :) )
     {
          // initialize other variables
     }
}

@end

I basically need to specifically call the BaseFooClass‘s init rather than the SubFooClass‘s init.

I cannot change the way the objects are initialized, as I am converting a project from C# to use in my iPad application.

Thank you all in advance

EDIT:

Due to someone asking, here is my header:

@interface BaseFooClass : NSObject

// implicit from NSObject
// -(id) init;

-(id) initWithSomeInt:(int) someInt;

// more methods

@end

@interface SubFooClass : BaseFooClass

// implicit from NSObject
// -(id) init;

// implicit from BaseFooClass
//-(id) initWithSomeInt:(int) someInt;


@end

Answer 1

Objective-C doesn’t work this way because of the way the runtime converts methods into function calls. Self is always an instance of the allocated class, even when invoking the super-class’s methods. You need to create your designated initializer for your BaseClassFoo and always go there. So you should be doing something like this:

@implementation BaseFooClass

-(id) init
{
  return [self initWithSomeInt:0]; // redirect super class's designated initializer
}

-(id) initWithSomeInt:(int) someInt
{
  if ((self = [super init])) // Designated initializer always calls into super class's designated initializer (in this case, NSObject's designated initializer is init
  {
    self.someInt = someInt;
  }

  return self;
}

@end

@implementation SubFooClass

// Here we don't override init because our super class's designated initializer
// is initWithSomeInt:
// -(id) init
// {
//   return [self initWithSomeInt:0];
// }

// we override this because it's our superclass's designated initializer, plus it
// is ours as well
-(id) initWithSomeInt:(int) someInt
{
  if ((self = [super initWithSomeInt:someInt]))
  {
    // initialize other sub-class specific variables
  }
}

@end