Re: [Pydispatcher-devel] dispatcher questions

[Mike C. F. <mcf...@ro...>]

Thomas Heller wrote:
...

>I hope this forum is the correct one to ask questions about Patrick's
>dispatcher module ;-)
>
Yup, this is the place.  Though I'm rather busy these days, so there may 
be considerable delays in response from me particularly.

>The problem occurs when the event handling become more complicated, and
>cannot simply be done by a simple (bound) method call in a widget
>instance.
>
>What I want to achive is something like this:
>
>    def on_create(self, widget):
>        name = widget.label
>        import registry
>        model = registry.get(name)
>        
>        def handler(model, widget=widget):
>            data = model.get_some_data()
>            widget.show_value(data)
>
>        dispatcher.connect(signal=(name, "changed"),
>                           receiver=handler)
>
>In other words, the handler for the event must do an operation on the
>model for some data, and then call a method on the widget. (The
>'changed' event in the above code has the model as a parameter to make
>this possible).
>
If I understand correctly, what you want to do is to have the handler 
function live a life of its own (not be collected) until the widget goes 
out of scope, at which point you want to drop the handler function.

class Holder( object ):
    def __init__( self, method, client ):
       self.method= method # strong reference, kept alive
       self.client = saferef.safeRef( client, onDelete = self.cleanup )
    def __call__( self, *args, **named ):
       if self.client:
           client = self.client()
           if client is not None:
              return self.method( *args, **named )
    def cleanup( self, oldWeakRef ):
       self.client = None
       dispatcher.disconnect( self )

I haven't tested that, but it should outline the basic approach.  You 
use weak=False when registering the Holder instance, and the holder 
takes care of managing the lifetime of the method (keeps a strong ref 
until the client widget goes away).

>Any ideas, anyone? Is this a common problem?
>
>Thomas
>  
>

Don't know how common it is, I've seen similar patterns in a few cases, 
but I do a lot of meta-programming. HTH,
Mike

_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/