CODEWITHSUNDEEP
objective-ccocoa
Nicholas
Nicholas

Reputation: 85

Accessing subclass instances

I have a Class with an instance variable of an NSArray of different objects I know should inherit from the same superclass. My question is how do I access the instance variables and methods from another class (its controller) while ensuring that the contents of the array contains only objects that are a subclass of a certain class? I tried implementing a minimal protocol and refencing the objects in the array as type id and (id *) but that won't let me access any instance variables or methods of the classes in the array (and rightly so). In object file

NSArray* components; // contains subclasses of component

In the controller file

subclassofClassObject* object;

is there a subclassOf function, macro, typedef ... etc or a workaround so I can reference the subclasses of component in a subclass of object from a subclass of controller. i.e something to replace subclassofClass.

Upvotes: 0

Views: 88

Answers (2)

CRD
CRD

Reputation: 53000

I don't quite follow what you're asking, but maybe the following will help:

You can determine if you have an instance of a class, or one of its subclasses using isKindOfClass:. For example given a class MyBaseClass, then use a cast:

id elem = [components objectAtIndex:ix];
if ([elem isKindOfClass:[MyBaseClass class]])
{
   // elem is an instance of MyBaseClass or one of its subclasses so cast is safe
   MyBaseClass *mbc = (MyBaseClass *)elem;
   // now can access methods, properties and public instance variables
   // of MyBaseClass via mbc without warnings
   ...
}

Upvotes: 0

Denis
Denis

Reputation: 6413

I'd suggest to think on your architecture design first. You can try to move your logic inside your subclasses implementation:

@interface BaseClass: NSObject {
}
...
- (void) doMySuperImportantStuff: (id)data;
@end

@implementation BaseClass
...
- (void) doMySuperImportantStuff: (id)data
{
  // basic implementation here, or common actions for all subclasses
  NSLog(@"BaseClass is here");
}
@end


@interface ClassA: BaseClass
{
NSInteger i;
}
...
@end

@implementation ClassA
...
- (void) doMySuperImportantStuff: (id)data
{
  // some specific stuff
  NSLog(@"ClassA is here, i=%d", i);
}
@end


@interface ClassB: BaseClass
{
  NSString *myString;
}
...
@end

@implementation ClassB
...
- (void) doMySuperImportantStuff: (id)data
{
  // another specific stuff
  NSLog(@"ClassB is here, myString = %@", myString);
}
@end

// client code example
....
NSArray *list = ...; // list of instances of the subclasses from BaseClass
for(BaseClass *item in list) {
  [item doMySuperImportantStuff: userData];
}

Upvotes: 2

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