# Scripts/kvo-debugging

- `Download example`

…

## kvo-debugging.py

    #!/usr/bin/env python
    """
    Experimental code, attempting to work around Apple's KVO hacks.
    """

    import objc
    from Foundation import (
        NSObject,
        NSKeyValueObservingOptionOld,
        NSKeyValueObservingOptionNew,
    )

    _kvoclassed = {}

    def dumpClass(cls):
        print("DUMP", cls)
        print(cls.__bases__)
        # for k, v in cls.__dict__.items():
        #    print k, v
        print("-" * 40)

    def toKVOClass(orig, new):
        if new in _kvoclassed:
            return new
        origdct = dict(orig.__dict__)
        origset = set(origdct)
        newset = set(new.__dict__)
        # Merge in non-methods from the dict
        for key in origset - newset:
            value = origdct[key]
            if isinstance(value, objc.selector):
                continue
            setattr(new, key, value)
        # Remember the original class,
        # KVO wants to go back to NSObject!
        _kvoclassed[new] = orig
        return new

    def fromKVOClass(new):
        return _kvoclassed[new]

    class FooClass(NSObject):
        _kvc_bar = None
        outlet = objc.IBOutlet("outlet")

        def XXaddObserver_forKeyPath_options_context_(
            self, observer, keyPath, options, context
        ):
            print(
                "addObserver_forKeyPath_options_context_",
                observer,
                keyPath,
                options,
                context,
            )
            orig = FooClass  # type(self)
            super(orig, self).addObserver_forKeyPath_options_context_(
                observer, keyPath, options, context
            )
            new = self.class__()
            print(orig, type(self), new)
            if orig is not new:
                print("class changed!!")
                self.__class__ = toKVOClass(orig, new)

        def XXremoveObserver_forKeyPath_(self, observer, keyPath):
            print("removeObserver_forKeyPath_", observer, keyPath)
            orig = type(self)
            super(orig, self).removeObserver_forKeyPath_(observer, keyPath)
            new = self.class__()
            print(orig, type(self), new)
            if orig is not new:
                print("class changed!!")
                self.__class__ = fromKVOClass(orig)

        def setBar_(self, bar):
            print("setBar_ ->", bar)
            print(self, type(self), self.class__())
            # print('->', bar)
            self._kvc_bar = bar

        setBar_ = objc.accessor(setBar_)

        def bar(self):
            print("bar", self._kvc_bar)
            # print(self, type(self), self.class__())
            return self._kvc_bar

        bar = objc.accessor(bar)

    class FooObserver(NSObject):
        def observeValueForKeyPath_ofObject_change_context_(
            self, keyPath, obj, change, context
        ):
            print(
                "[[[[[]]]]] observeValueForKeyPath_ofObject_change_context_",
                keyPath,
                obj,
                change,
                context,
            )
            dumpClass(type(obj))

        def willChangeValueForKey_(self, key):
            print("[[[[[]]]]] willChangeValueForKey_", key)

    foo = FooClass.alloc().init()
    fooObserver = FooObserver.alloc().init()

    print()
    print()
    print("***** unobserved set")
    print(foo.bar())
    foo.setBar_("0shw00t")
    print(foo.bar())

    print()
    print()
    print("***** observing, setting three times")
    print("foo's ISA:", foo.pyobjc_ISA)
    print("Adding an observer")
    foo.addObserver_forKeyPath_options_context_(
        fooObserver, "bar", (NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld), 0
    )
    print("foo's ISA:", foo.pyobjc_ISA)
    # foo.removeObserver_forKeyPath_(fooObserver, u'bar');sys.exit(1)
    print(foo.bar())
    foo.setBar_("1w00t")
    print(foo.bar())
    foo.setBar_("2sw00t")
    print(foo.bar())
    foo.setBar_("3shw00t")
    print(foo.bar())

    print()
    print()
    print("***** removing the observer and setting twice (unobserved)")
    foo.removeObserver_forKeyPath_(fooObserver, "bar")
    print(foo.bar())
    foo.setBar_("4sw00t")
    print(foo.bar())
    foo.setBar_("5w00t")
    print(foo.bar())

    print(foo.__class__)