Re: [Rubycocoa-talk] [XCode] GDB (debugger) and NSOutlineView[MESSAGE NOT SCANNED]

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

On 16 Feb 2006, at 16:28, Yvon Thoraval wrote:

>> How are these methods implemented, and what types of values are  
>> the items you are returning? They must be NSObject subclasses, and  
>> you must keep a reference to them somewhere - otherwise they will  
>> be garbage collected and things will go wrong.
>

> for :
> 	def outlineView_child_ofItem(aTree, index, bookmark)
> i return a REXML::Element :
>       return children[index]


OK, this is the problem. NSOutlineView doesn't retain the object  
returned from this method. Since REXML::Element is not derived from  
NSObject, the object NSOutlineView sees is a temporary proxy for the  
ruby instance. Since the proxy is temporary, NSOutlineView gets  
confused because it expects to see the same object later.

Here's a workaround for the moment (until there's a better solution  
in RubyCocoa core):

# Define helper class
class OutlineViewProxy < OSX::NSObject
   ns_overrides :init
   def init(slave)
     super_init
     @slave = slave
     self
   end
   def slave
     ObjectSpace._id2ref(@slave) # used to prevent GC cycle
   end
end

# One instance of helper class per plain ruby object being helped
module NSOutlineViewable
   def to_nsobj
     # This will be released with ruby instance is GC-ed
     @__nsoutlineviewproxy ||= OutlineViewProxy.alloc.init(self)
   end
end

# Include the helper module in REXML::Element
module REXML
   class Element
     include NSOutlineViewable
   end
end

# Now, in any of your outlineView methods that takes an 'item' argument,
# you must get at the real object by using 'slave' first.
# e.g.,

   def outlineView_isItemExpandable(aTree, bookmark)
     return bookmark.slave.has_elements?
   end

Let me know if that works for you.
Jonathan