Re: [Pydispatcher-devel] dispatcher questions

[Thomas H. <th...@py...>]

"Mike C. Fletcher" <mcf...@ro...> writes:

> 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).

Mike, thanks for this suggestion. It didn't work exactly as shown above,
but it showed me the way to do it. I assume you meant
        self.client = weakref.ref(client, self.cleanup)
instead of
        self.client = saferef.safeRef( client, onDelete = self.cleanup )
or did I miss something.

And sorry for the late reply.

Thomas