Re: [Rubycocoa-talk] SyncServices and RubyCocoa

[Jonathan P. <jp...@dc...>]

On 7 Nov 2005, at 19:00, Rupert BARROW wrote:

> 2005-11-07 19:55:36.494 SimpleStickies[782] Exception syncing:  
> NSUnknownKeyException, reason [<Note 0x651130> takeValue:forKey:]:  
> attempt to assign value to unknown key: 'primaryKey'.
> This class does not have an instance variable of the name  
> primaryKey or _primaryKey, nor a method of the name setPrimaryKey,  
> or _setPrimaryKey
>
> This is strange since dumping the instance_methods of Note shows  
> that all the expected methods are there :
> setCreateDate
> createDate

I think these are ruby-level instance methods - not actually known to  
Objective C. The Objective C -> ruby bridge is accomplished through  
the ObjC equivalent of Ruby's method_missing.

>
> So, do you think that SyncServices are using some route which is  
> bypassing our kvc_wrapper mechanism to reach the primaryKey  
> "attribute" and getter and setter ?

I think the problem is that SyncServices is indirectly checking the  
Objective C class for a method primaryKey or _primaryKey and failing  
because they don't exist. The key-value-coding support in RubyCocoa  
is implemented by hooking into the valueForUndefinedKey: method that  
KVC calls if such a method doesn't exist. It seems that SyncServices  
is using another route that doesn't use that method. (this is my  
guess - haven't looked into it further)

It might be possible to resolve the problem, by defining the methods  
in question in Objective C land. There is a special RubyCocoa method  
to help you do this. Take a look at the kvc_array_accessor method  
declared in oc_import.rb. It uses addRubyMethod_withType to add a  
real ObjC method that calls through to a Ruby method. So you'd  
convert your kvc_wrapper_representation to look something like  
(untested):

         def kvc_wrapper_representation(*keys)
             keys.each do |key|
                 set_key = "set" + key
                 set_key[3..3] = set_key[3..3].upcase
                 class_eval <<- 
EOE_KVC_WRAPPER_REPRESENTATION,__FILE__,__LINE__+1
                     def #{key}
                         @_representation.valueForKey("#{key}")
                     end
                     def #{key}=(val)
                         self.willChangeValueForKey("#{key}")
                         @_representation.setValue_forKey(val, "#{key}")
                         self.didChangeValueForKey("#{key}")
                     end
                     def #{set_key}(val); self.#{key}= val; end
                     EOE_KVC_WRAPPER_REPRESENTATION
                     self.addRubyMethod_withType("#{key}".to_sym,  
"@4@8:12")
                     self.addRubyMethod_withType("# 
{set_key}:".to_sym, "@4@8:12@16")
             end
         end

Having thought about this a bit more, it may be cleaner to 'improve'  
the implementation of kvc_reader and kvc_writer to define these  
methods and call through to the appropriate ruby setter/getter. Then  
you'd implement the delegation to @_representation in a normal ruby  
accessor.

Hope that makes some sense :)

Jonathan