On Mar 11, 2015, at 15:03 , Sean McBride <s...@rogue-research.com> wrote:
> It's here:
I just spent a few minutes with it. A couple of things:
— I don’t think it’s a very good idea to do this (slightly abbreviated from
your source):
> - (void)bind:(NSString*)inBindingName toObject:(id)inObservableObject
> withKeyPath:(NSString*)inKeyPath options:(NSDictionary*)inOptions {
> [inObservableObject addObserver:self forKeyPath:inKeyPath options:0
> context:context];
> [super bind:inBindingName toObject:inObservableObject
> withKeyPath:inKeyPath options:inOptions];
> }
The standard implementation of bindings, which you’re using when you invoke
super, *also* adds the exact same observation as you just did (though with a
different or nil context, presumably).
When you invoke super in ‘unbind', I guess it’s using the context-less form of
removeObserver.
I don’t have an explanation of exactly why that might fail, but it certainly
seems a lot like the conditions for bug I talked about earlier. You have the
same object observing the same property of the same target twice.
I would suggest you simply don’t do this to the binding, or better still don’t
use a binding here at all. But of course my opinion here is basically
valueless, since I don’t know the design of your app.
— I commented out the super ‘bind’ in the above method to see what would
happen. After also commenting out the various asserts, I ended up with this log
output:
> •BIND: ptr: 0x610000140bb0, tag: 1, name: "crosshairsTransform", context:
> 123456
> •BIND: ptr: 0x610000140c60, tag: 2, name: "crosshairsTransform", context:
> 123456
> •BIND: ptr: 0x610000140b00, tag: 3, name: "crosshairsTransform", context:
> 123456
> •OBSERVE: ptr: 0x610000140bb0, tag: 1: keyPath: "selection.crosshairs",
> context: 123456
> •OBSERVE: ptr: 0x610000140c60, tag: 2: keyPath: "selection.crosshairs",
> context: 123456
> •OBSERVE: ptr: 0x610000140b00, tag: 3: keyPath: "selection.crosshairs",
> context: 123456
> •UNBIND: ptr: 0x610000140c60, tag: 2, name: "crosshairsTransform", context:
> 123456, hasInfo: 0
> •UNBIND: ptr: 0x610000140b00, tag: 3, name: "crosshairsTransform", context:
> 123456, hasInfo: 0
> •DEALLOC: ptr: 0x610000140b00, tag: 3
> •DEALLOC: ptr: 0x610000140c60, tag: 2
> •OBSERVE: ptr: 0x610000140bb0, tag: 1: keyPath: "selection.crosshairs",
> context: 123456
which I think is the behavior you’re looking for. (Of course, the app crashed
shortly after that, because the object controller didn’t have any content, or
some such consequence of the missing binding.)
To my mind, that confirms that the multiple-identical-observation scenario is
the problem.
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