On 2012 May 21, at 21:52, Quincey Morris wrote:
> On May 21, 2012, at 20:44 , Jerry Krinock wrote:
>> -(void)setRating:(float)rating
>> {
>> // Stuff to make reverse binding work…
>> NSDictionary* bindingsInfo = [self infoForBinding:@"rating"] ;
>> id object = [bindingsInfo objectForKey:NSObservedObjectKey] ;
>> NSString* bindingsPath = [bindingsInfo objectForKey:NSObservedKeyPathKey]
>> ;
>> [object setValue:[NSNumber numberWithFloat:rating]
>> forKeyPath:bindingsPath] ;
>>
>> // Set ivar, needsDisplay
>> …
>> }
>
> This seems more or less the correct approach to defining a custom binding.
> "More or less" because you may have committed some minor technical violation
> of custom binding implementations, described unintelligibly in this document:
>
>
> https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaBindings/Concepts/HowDoBindingsWork.html
So, five weeks later, I learn that I probably was committing a minor technical
violation.
Pushing a value into the data model whenever a value is set in the view is not
a good idea. Such a push will occur, for example, whenever the selection
changes, which is of course not necessary. In fact, it can do some damage…
Tonight I modified my Inspector to support editing values in a multiple
selection, for example:
• Select 10 model objects.
• Inspector indicates "Multiple Selection".
• Click the 3rd star in the Inspector's Star Rating View.
• I might put a warning sheet here, "Are you sure you want to change 10 items,
blah?"
• All 10 objects get a 3-star rating.
But after I bound instead to a "multiFoo" class to make that work, I found that
the extra setting of the data model was causing model values to be copied from
one model object to the next when the I simply selected one model object and
then changed the selection to a different model object.
A better place for pushing the value to the data model is in the input-handling
method of the view, -mouseDown: in the case of my star rating control. Moving
the above code to -mouseDown: fixed the problem.
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