Thanks for the suggestions, all. I think this will probably suit my needs for now.
Mikkel
On 12/02/2011, at 17.06, Andy Lee wrote:
> "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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