Objective-C call specific class method

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

Why would that be necessary? This is the only method that gives me problems... — Richard J. Ross III, Oct 07 '10 at 12:28

score 3 · Accepted Answer · answered Oct 07 '10 at 13:19

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

I used this answer with some modifications: I renamed the `init` method in the `BaseFooClass` to `_initializeInstanceVariables` and Called that after I called `[super init], and It works great now, thank you!! — Richard J. Ross III, Oct 07 '10 at 13:39

nacho4d · Answer 2 · 2010-10-07T13:13:03.863

1

You have to call [super initWithSomeInt:someInt]; in the init method of your SubFooClass. ;)

ADDED: I think is weird you try to call init within iniWithSomeInt . The usual thing would be to call [super initWithSomeInt:someInt] in initIthSomeInt method of SubFooClass and change what you need inside the if clause.

edited Oct 07 '10 at 13:13

answered Oct 07 '10 at 13:01

nacho4d

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That results in the same stackoverflow error. The problem is on the line (Edited) shown.. – Richard J. Ross III Oct 07 '10 at 13:02

Objective-C call specific class method

2 Answers2