Sorry to answer a question with a question, but will this really do
what you want?
I see from the docs that the @optional keyword means the method is not
required. Doesn't that mean you can conform to the Check protocol
without implementing -optionalMethodToImplement, which would mean that
-conformsToProtocol: could give you a misleading answer? (I would
check this myself with some test code, but I don't have enough time
right this second.)
If the above is correct, I suppose you could take out the @optional
keyword, but personally, I prefer the category approach that Jens
Alfke suggested rather than using protocols at all. Then you don't
have to change your class declaration in order to tell yourself that a
given class implements a given method. You can just ask the object
*directly* whether it implements the method. This makes it easier to
change your mind about whether and where to implement -
optionalMethodToImplement, because you don't have to remember to
change class declarations.
--Andy
On Apr 29, 2008, at 4:40 PM, K. Darcy Otto wrote:
The casting worked, and the protocol gets found; but I'm still
getting a warning that the protocol is not found. Here's what I have:
Superclass.h:
@protocol Check;
Superclass.m:
@protocol Check
@optional
-(BOOL)optionalMethodToImplement;
@end
(I'm relegating the protocol to the .m file to make it "private" in
a sense.)
Subclass.h
@interface Subclass : Superclass <Check>
...
Now, the compiler issues a warning at the @interface line in
Subclass.h - "no definition of protocol 'Check' is found". But it
is clear that the protocol is being located at runtime nevertheless,
because if I eliminate <Check> from the @interface line,
optionalMethodToImplement: does not get called. Also, what is
interesting is that if I move @protocol Check ... @end in
Superclass.m to Superclass.h, the warning goes away. So, is there a
way to keep @protocol Check ... @end in Superclass.m and eliminate
the warning?
Thanks.
On 28-Apr-08, at 11:25 PM, Michael Vannorsdel wrote:
You can make the superclass's method look like this:
- (void)doSomething
{
if([self conformsToProtocol:@protocol(Check)])
[(SuperClass <Check> *)self optionalMethodToImplement];
}
The cast eliminates the compiler warning.
As far as making it private it depends what you mean by that. If
you don't want it visible in headers you're going to distribute you
can put:
@protocol Check;
in the public header then actually define the whole protocol in a
private undistributed header.
On Apr 28, 2008, at 9:22 PM, K. Darcy Otto wrote:
Okay, I have done this, and things are compiling and running
correctly. Thank you. Two additional questions then. First, I
still get the warning that the superclass "may not respond" to the
method (and to be sure, it is only implemented in the subclass,
but the superclass calls it after a conformsToProtocol: check).
Second, I would like the optionalMethodToImplement to be private -
usually I put this in the .m file under a category; but when I do
that with the protocol, the subclass cannot locate the protocol.
Any suggestions?
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