"super" does not change what class the object thinks it is an instance of.
(It's different from C++ in this way, if I remember my C++.) If an object is an
instance of class X, [self class] *always* returns X.
Suppose you call [obj tagDict] where obj is an instance of SubClass. This is
what happens:
"if ([self class] ..." fails, so you fall through to the [super tagDict] call.
The message dispatcher sees the "super" and looks for an implementation of
tagDict one level up in the class hierarchy, and finds that SuperClass
implements it, so it calls that implementation.
"if ([self class] ..." again fails (because [self class] still returns
SubClass), so again you fall through to the [super tagDict] call. The message
dispatcher looks for an implementation of tagDict one level up in the class
hierarchy, but SuperClass's superclass does not implement tagDict, hence the
error.
I *think* this is what's happening. To test my theory, use the debugger or
NSLog statements to trace the logic that is being executed.
You can fix this by doing something like this (note this is quick untested code
and there might be a smarter and/or more efficient approach):
-(NSDictionary *)tagDictForClass:(Class)aClass
{
NSMutableDictionary *dict = //built from plist, different for each class
if (aClass == [SuperClass class]]) {
return dict; // we don't go above our own root
}
NSDictionary *superDict = [self tagDictForClass:[aClass superclass]];
[dict addEntriesFromDictionary:superDict];
return dict;
}
-(NSDictionary *)tagDict
{
return [self tagDictForClass:[self class]];
}
--Andy
On Feb 12, 2011, at 8:52 AM, Mikkel Eide Eriksen wrote:
> Hi all,
>
> I think I may have misunderstood something about how super works. In trying
> to build a dictionary that contains key/value pairs from the class itself as
> well as super classes up to an arbitrary height, I've hit a wall. Simplified,
> I have two classes, SuperClass and SubClass. In SuperClass, the following
> method is implemented:
>
> -(NSDictionary *)tagDict
> {
> NSMutableDictionary *dict = //built from plist, different for each class
> if ([self class] == [SuperClass class]) {
> return dict; // we don't go above our own root
> }
>
> NSEnumerator *keyE = [[super tagDict] keyEnumerator]; //HERE
> id key;
>
> while (key = [keyE nextObject]) {
> [dict setValue:[[super tagDict] valueForKey:key]];
> }
>
> return [dict copy];
> }
>
> When this runs, it works fine if I call tagDict on an instance of SuperClass,
> but if I try with SubClass, I get:
>
> -[SubClass tagDict]: unrecognized selector sent to instance 0x20038efe0
>
> But shouldn't it keep calling upwards until I reach the SuperClass, then stop
> and return my finished dict? I see that it appears to be calling [SubClass
> tagDict] which is the very method it's already in (so the selector can't very
> well be unrecognized, or what?)...
>
> Regards,
> Mikkel_______________________________________________
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