Question

I have a class that does some generic code for Writing to a Database. Bring up the popovers, and controls, etc. Though there are many types of elements that I can write out to the database, each sub-class needs to have its own -(void) writeTagValue selector to implement the element’s write.

The base-class has a selector that does the call to self.writeTagValue though since the base class does not really do any writing, its -(void) writeElement selector is empty with an abort(); in it.

I’ve implemented a protocol in the base class.h

@protocol IoUISEWriteAnimation <NSObject>
  -(void) writeTagValue;
  -(IBAction)saWriteValue:(NSNotification *)notification;
@end

added the protocol to the Sub-classes and now if the sub-classes don’t define the selectors, I get compiler warnings.

What I want to know is, is there a way to remove the empty -(void) writeElement selector in the base class?

Answer 1

You can do something like this:

@protocol MyProtocol<NSObject>

@required 
-(void) myRequiredMethod;

@optional
-(void) myOptionalMethod;

@end

And when you need to call an optional method, you do something like this:

if ([delegate respondsToSelector:@selector(myOptionalMethod)])
   [delegate myOptionalMethod];
else
   // abort, or ignore.