On Jan 11, 2009, at 05:25, Russell Martin wrote:
Here's the source of changeKeyPath:
- (void)changeKeyPath:(NSString *)keyPath
ofObject:(id)obj
toValue:(id)newValue
{
// setValue:forKeyPath: will cause the key-value observing method
// to be called, which takes care of the undo stuff
[obj setValue:newValue forKeyPath:keyPath];
}
OK, so you've found the definition of the method. You certainly can't
tell from this definition alone whether it's overriding something
else, but you've eliminated the possibility of its overriding
something else in your (or Hillegass's) code by searching for it, and
you've eliminated the possibility of its overriding something in the
Cocoa frameworks (or something similar, like being a delegate method)
by checking the documentation. So it's just a method.
I tried this. 'Jump to definition' stays right where I started, at
the one and only implementation of changeKeyPath in my MyDocument.m
file. Also, searching for changeKeyPath in all of my project file
shows only the one instance in MyDocument.m. This is why I was
thinking that I was overriding a super's method or implementing a
delegate method.
...
Nope. Not getting a compile error. I even cleaned all targets and
rebuilt just to make sure. The program builds and runs and does what
Hillegass says it will do. He's got an email address listed in the
book for feedback, I guess I should give him some because to a
complete beginner (which is what this book is for), it's a complete
mystery as to why:
a) I don't have to provide any earlier declaration of changeKeyPath
This is true, under certain conditions. If nothing in the .m file
containing the definition refers to it *before* the definition, and
nothing in any other .m file refers to it at all, then there's no need
to have a separate declaration ("stub"). [This is a useful technique
for methods that are private to the .m file, BTW, since it runs no
risk of exposing the method to the outside world.] As I noted before,
that's true of *any* definition in C, whether it's a variable or a
function (or a method in Objective-C). If you need to use the method
elsewhere, just add a declaration in the @interface of the .h file
corresponding to the .m file.
b) no other method calls it in the program
Could be. Since this a method you (or Hillegass) wrote, it won't be
called unless you write code to call it.
c) I just added a an NSLog call to it, built, put the program
through its paces and it never seems to get called.
See (b).
d) I just commented it out and it doesn't seem to affect the
program's functionality at all
See (b).
e) I might have just been wasting everyone's time, and if so, please
let me apologize for that.
Not a problem, and I don't think you were so terribly tangled up after
all. If you can work out where you're supposed to call this method
(and you'll have to refer to Hillegass's book for that -- maybe he
doesn't have you use it until a later section), you'll work out
whether you're going to need the declaration in the .h file, or
whether you can take the shortcut of omitting the .h file declaration.
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