Re: Subclassing Catch-22

FROM : Todd Ransom
DATE : Tue Apr 26 23:17:27 2005

The code looks like this:

- (NSString *)bindingKeyForTableColumnIdentifier: (NSString
*)identifier {

   NSArray *keys = [NSArray arrayWithObjects: @"name", @"notes",
@"status", nil];
   NSArray *identifiers = [NSArray arrayWithObjects: @"Name", @"Notes",
@"Status", nil];

   NSDictionary *keyForIdentifier = [dictionaryWithObjects: keys forKeys:
identifiers;

   return [keyForIdentifier valueForKey: identifier];
}

- (BOOL) tableViewAddColumnWithIdentifier: (NSString *)identifier {

   NSString *bindingKey = [self bindingKeyForTableColumnIdentifier:
identifier];

   [create a table column, bind it, add it to a table]

}

The theory was that subclasses would override both methods, returning
the appropriate key to bind to and implementing whatever specifics were
required for the table column (popup button cells, date formatters,
etc.).

It all worked fine except I wanted the subclasses to defer to super for
columns shared by all views.

Todd Ransom
Return Self Software
http://returnself.com
On Apr 26, 2005, at 2:57 PM, Greg Titus wrote:

>
> On Apr 26, 2005, at 20:28, Todd Ransom wrote:

>> I have a controller class that has methods like this:
>>
>> - (BOOL)doSomething;
>> - (NSString *)getInformationRequiredToDoSomething;
>>
>> - (BOOL)doSomething {
>>
>>    NSString *info = [self getInformationRequiredToDoSomething];
>>    ...
>> }
>>
>> Which works fine until I subclass. In my subclass I would like
>> doSomething to call super for a subset of possible actions. But when
>> I call super it calls [self getInformationRequiredToDoSomething] and
>> returns its own info, not super's.

>
> The pattern for this would be to make the superclass actually
> implement:
>
> - (NSString *)internalInformationRequired;
> {
>     ...
> }
>
> - (NSString *)getInformationRequiredToDoSomething
> {
>     return [self internalInformationRequired];
> }
>
> - (BOOL)doSomething
> {
>     NSString *info = [self internalInformationRequired];
> }
>
> Then even if you override getInformationRequiredToDoSomething in a
> subclass, the superclass's doSomething will get the original
> information from the superclass. But like Ondra, I suspect that there
> may be a better way to design this, if I had more information on what
> you are trying to do.
>
> Hope this helps,
>      - Greg
>     
>