[Glade-devel] Property Binding: Fixing the big blocker

Am 18.11.2011 19:49, schrieb Tristan Van Berkom:
On Fri, Nov 18, 2011 at 2:24 AM, Denis Washington<denisw at online.de>  wrote:
Am 15.11.2011 22:44, schrieb Tristan Van Berkom:

I think that it's obvious the mechanism is needed, but I dont think that
should clear bindings based on sensitivity state, in other words I would
rather that sensitivity always be the last thing which is evaluated based
on other real states (it doesnt seem to make sense that we drive a 'real'
project state based on the 'virtual' sensitivity state, and I fear with
complexity of Glade that that will bite us later on).

So, for the scenario you described above, functionally speaking I
think this needs
to happen:

   o Button editor sets the edit mode and does glade_command_push_group()
   o Button editor does it's normal command group routines
   o Button editor invalidates the "label" property (note: this
invalidation does not exist)
   o Invalidating the "label" property causes bindings to that label to
become invalid, in
      fact anything which "refers to that property" is invalid, today
this can only be a binding
      of another property.
       o A widget has a property which was bound to the "label"
property which was invalidated,
          as a consequence of that action, it's binding to the said
label is undoably cleared
       o GladeWidgetAdaptor->evaluate_sensitivity ( use_command = TRUE
) is called on
          that target property's widget to re-evaluate sensitivity
states after having changed
          the binding state
   o All widgets with any binding to the invalidated label finish
adjusting themselves to the
   o Button editor calls GladeWidgetAdaptor->evaluate_sensitivity (
use_command = TRUE )
      on itself to evaluate the sensitivity after having changed it's
own "edit mode"
   o Finally glade_command_pop_group() is hit

The "invalidation" above might be a signal from the source
GladeProperty which has
a strict meaning, or possibly just a function
which loops over all the targets, unsets them and resolves the
sensitivity of the
target widget.

I am not sure how the additional "invalidation" command you envision would
conceptually differ from glade_command_set_sensitive (sensitive = FALSE).
While I understand your intention, the fact that the property sensitivity
*does* affect the binding state still remains in your proposed design; it is

And enter the confusion:

    a.) Bindings use this virtual state of 'sensitivity' to clear themselves
    b.) Anything else... like activatable properties, looks at the code you
         wrote and decides that it's also a good idea to clear itself when it
         something goes insensitive
    c.) Code competes for real states because of insignificant
sensitivity changes

Yes, it is important that when one editor sets a property insensitive,
the binding
updates/clears itself, however it is also important that that clearing
is not simply
*because* of the sensitivity state.

OK, I think I know where you're getting at now. You want to ensure that 
the binding removal only happens if a property is made sensitive because 
it is invalidated by an Editor, not because of any other random kinds of 
property sensitivity changes. Seen this way, a separate "invalidation" 
command is surely a superior design.

At any rate, if you were to drive the project states from the sensitivity state,
you would still need to find a way to do it undoably while the sensitivity is
set as a command.

i.e. it's important that:

   a.) Editor sets activatable stuff that makes a property insensitive
   b.) Property undoably goes insensitive
   c.) Binding is undoably unset

a, b and c have to happen as part of the same command group (so you
cant very well listen to a sensitivity changed signal and clear the
binding state).

just indirected by the "invalidate" command. Also, the "invalidation" logic
in the Editor would inevitably duplicate the logic in
GladeWidgetAdaptor->evaluate_property_flags() (or ->evaluate_sensitivity(),
we we're going to call it), meaning that changes to that logic alway
requires modifications to two places (error-prone). In short, I think this
needlessly complicates things without benefit.

For reference, this is how the process works currently in the
"command-set-sensitive" branch:

1. The Editor does glade_command_group_push() and does what it has always

2. Editor calls "GladeWidgetAdaptor->adjust_property_flags (use_command =
TRUE)". That function's implementation uses
glade_command_set_property_sensitive(), which checks whether any bindings
become invalidated by the sensitivity change and, in turn, calls
"glade_command_bind_property (binding_target, NULL)" as needed (grouped with
the original sensitivity-setting command).

Right, so in this specific step we have code that explicitly writes out that if
you set a property insensitive... *only* bindings are effected, which singles
out bindings as some kind of a special case feature.

This is where a generalized "clear property" with a general meaning would
be better.

Actually, I agree with this now. A separate notion of invalidation is 
much clearer and less fragile. Given that, we might even be able to omit 
glade_command_set_property_sensitive() and call 
GladeWidgetAdaptor->evaluate_sensitivity() from the invalidation command 

Historically you need to know that all the worst code ends up in glade-command.c
because we are too lazy to do things properly, then we add adaptor methods to
do things more generically and pull hard-code out of glade-command.c... I'm just
trying to avoid that.

So you're thinking of something like GladeWidgetAdaptor->invalidate()? 
How would that be better than simply having 
glade_command_invalidate_property()? I cannot think of any way thank 
specific widget types would need different implementations of this.


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