Question

I have 3 classes of objects. All 3 classes share some properties in common, as color, text, etc.

For example, I can have this

Class1 *objectA = [[Class1 alloc] init];
objectA.myColor = [UIColor redColor];

Class2 *objectB = [[Class2 alloc] init];
objectA.myColor = [UIColor redColor];

Class3 *objectC = [[Class3 alloc] init];
objectA.myColor = [UIColor redColor];

… etc.

Now I need, for example, to create a method that can change the color of a given object, whatever class it represents.

A typical method would be

- (void) changeColor:(Class1*) myOBJ toColor:(UIColor*)myColor {
   myOBJ.color = myColor;
}

when in fact I need this

- (void) changeColor:(???) myOBJ toColor:(UIColor*)myColor {
   myOBJ.color = myColor;
}
// what to put on ??? to make it generic? Is this a "whatever" kind?

thanks

---

EDIT

the problem of using this approach

- (void) changeColor:(id)myOBJ toColor:(UIColor*)myColor {
   if ([myOBJ respondsToSelector:@selector(setColor:)]) {
       myOBJ.color = myColor;
   }
}

is this. Imagine I want to set the frame of the object.
Then I will have to have this:

- (void) changeColor:(id)myOBJ newFrame:(CGRect)myFrame {

 if ([umID isKindOfClass:[Class1 class]]) {
   Class1 *oneObj = (Class1 *)myObj;
   oneObj.frame = myFrame;
 }

 if ([umID isKindOfClass:[Class2 class]]) 
   Class2 *oneObj = (Class2 *)myObj;
   oneObj.frame = myFrame;
 }


 if ([umID isKindOfClass:[Class3 class]]) 
   Class3 *oneObj = (Class3 *)myObj;
   oneObj.frame = myFrame;
 }

}

in other words, I will have to repeat the same stuff 3 times… right?

in other words, the problem is not solved as this is the same of having 3 methods, one for each class.

Answer 1

Maybe you can use protocols? Make Class1, Class2 and Class3 conform to a protocol with a property myColor. Then you could have a method like this (assuming your classes are of type UIView and your protocol is called ColorProtocol):

- (void) changeColor:(UIView<ColorProtocol>*) myOBJ toColor:(UIColor*)myColor {
   myOBJ.color = myColor;
   myOBJ.frame = ...;
}

Here is what your protocol definition could look like:

@protocol ColorProtocol

@property (nonatomic, retain) UIColor *myColor;

@end

Change your class definition files (.h) as follows to specify that you will conform to the protocol:

interface Class1 : UIView <ColorProtocol> {...}

In the implementation files (.m) you must simply synthesize the myColor property to conform to the ColorProtocol:

@synthesize myColor;

If your classes are very similar, using inheritance might be even simpler though. Check out Philip Regan’s answer.