[bug #22246] problem with key value observation

[Fred Kiefer]

URL:
  <http://savannah.gnu.org/bugs/?22246>

                 Summary: problem with key value observation
                 Project: GNUstep
            Submitted by: FredKiefer
            Submitted on: Donnerstag 07.02.2008 um 08:42
                Category: Base/Foundation
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

In gui I use KVO to implement KVB. The last change I made on that some time
ago should allow a back chanel from the user inteface elements to the bound
controller. Now this bit is failing. For a check box I get a strange effect.
When I switch this checkbox on by clicking on it, it is shown on very shortly
but gets switched off again immediatly. Debugging this showed that the call to
setValue:For: on the controller results in three changes reported back to the
user interface. One from the actual setSomething: method in the controller
class (which is fine), one from takeValue:For: (which could be switched off,
as far as I understand the code) and one from setValue:For:. 
Now there should be a way that the KVO mechanism is able to tell that it
already send the notification for a change and use the underlying methods of
the base class to change the value, not the cooked up methods from the special
class. But this isn't the real problem, what makes it worse for me is that the
set value changes. This seems to happen in the takeValue:For: call, as I get
the correct value once and then twice the wrong one.
It is this later behaviour that I don't understand. Anybody with an idea,
what may be happening?




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