[MacRuby-devel] Bindings only working one-way

[John Shea]

Hi Michael,

I too have difficulties with IB and bindings - mainly because they are  
hard to debug - well I find them so (and not just in MacRuby).

When in doubt I blame an IB setting.

I quickly threw together something similar to what you have (except  
with sliders) , and pretty quickly came to the conclusion that it was  
not working ;-) - as soon as I embedded my working object into a  
matrix the KVO stopped working.

  I could get it working quickly sans matrix.

For morale and momentum I would suggest you get things working without  
the matrix first.

Using MacRuby attr_accessor (at least in my experience) will give you  
all the kvo magic but if you have a manual changing of the observed  
value you have to use the given (implicit) setter.

for example:
attr_accessor :billy # will create setter and getter for billy with  
all the appropritate KVO methods

def updateMyValue(sender) #called from a button perhaps
	setBilly(4)
end

#or setValue:4 forKey:billy

#@billy = 4 will not work, because it bypasses the accessor methods


So you don't need to override the accessors unless you are doing some  
additional work.

If you do override the accessors then you will have to put the whole  
willChangeValueForKey, and didChangeValueForKey  calls in your  
overwritten method.
In your code below you do override the accessor, and therefore lose  
the KVO.

If you are getting stuck on the simplest of binding I can send you a  
small project adapted from Hillegass which has an example of KVC.

Re matrix difficulties, a more experienced Cocoa person than me must  
proffer an explanation ;-).

Hope that helps,
cheers,
John

On Nov 22, 2008, at 1:01 AM, Michael Winterstein wrote:

> I'm having difficulty working with bindings and I'm not sure if it's  
> a MacRuby thing or my poor understanding of how they work.
>
> I've tried binding to two types of things - an NSMatrix of radio  
> buttons (binding to "selectedTag") and a Checkbox value.
>
> Using just an attr_accessor - the variable changes when the user  
> changes them, but changing the variable doesn't update in the UI.
>
> So I added an explicit setter method and to change the variable, I  
> use self.setVideoSource(VID_USE_S2) to modify it.
>
> This works to change it on-screen, but now UI changes aren't getting  
> through to the variables properly.  The NSMatrix variable isn't  
> changing, and the other variables are changing but are no longer  
> Boolean.  (If I do a "p x" I get  either #<NSCFBoolean:0xa07f13f8>  
> or #<NSCFBoolean:0xa07f1400>.
>
> I tried replacing 'attr_accessor' with 'attr_reader', and adding an  
> explicit getter. That results in the following when I run (even if I  
> add a 'return nil' to my setter method):
>
> [4169:10b] KVO autonotifying only supports -set<Key>: methods that  
> return void. Autonotifying will not be done for invocations of - 
> [MainWinController setVideoSource:].
>
> I haven't yet tried manual notification because I'm not likely to  
> use bindings for this case if that much work is required.  Is this  
> the expected way to go, or am I missing something here?
>
>
>
> Here's a bit of the code (these are set as keys in IB).  When used  
> elsewhere, I just have them as the instance variable :
>
> attr_accessor	:audioIncludeS1		# whether to include audio
> attr_accessor	:audioIncludeS2		# for a particular channel
> attr_accessor   	:videoSource		# which source to use (if any) for  
> video
> 	
> def setAudioIncludeS1(value)
>     @audioIncludeS1 = value
> end
>
> def setAudioIncludeS2(value)
>     @audioIncludeS2 = value
> end
>
>
> def setVideoSource(value)
>     case value
>         when VID_USE_S1
>             @videoSource = VID_USE_S1
>         when VID_USE_S2
>             @videoSource = VID_USE_S2
>         when VID_USE_NONE
>             @videoSource = VID_USE_NONE
>         else
>             @videoSource = VID_USE_NONE
>     end
> end
>
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