[Drawkit] Object manipulation notification

[Graham Cox]

On 1 Jul 2008, at 7:32 pm, Linan Wang wrote:

> Thank you for your response.
> For object adding/removal issue, I think it would be great if it could
> be implemented in KVO style, that is, programer can just observe the
> "objects" key of any DKObjectOwnerLayer.


Agreed, and I have changed the code for DKObjectOwnerLayer so that it  
is fully KVC/KVO compliant for the 'objects' property. In addition, I  
added notifications for adding/removing objects, so you have the  
choice over which to use. Note that I may have to tweak the KVC stuff  
to be more efficient - at present when adding or removing multiple  
objects it sends a notification per object rather than grouping them  
(which requires manual KVO notification), which could cause a blizzard  
of notifications for some operations. All the existing methods for  
object adding/removal now call the KVO-compliant ones so any operation  
should be observable.

> For object properties changing notifications: my program binds a
> "building" object with each DKDrawableObject (I put it as userInfo), I
> want to change the location/size/orientation properties of the objects
> when user manipulates the DKDrawableObject, so that extra info will be
> supplied to users to help them make design decisions.
> I feel it could be only achieved effeciently by hook
> postNotificationName:selector:object into methods which change the
> DKDrawableObject properties.
> Any thoughts?
> Thanks


I overlooked a more obvious thing in my last reply - there is a  
notification: kDKDrawableDidChangeNotification (this may have gone by  
another name in the beta 3) which is broadcast from the - 
notifyVisualChange method of DKDrawableObject that will tell you that  
*something* changed - you'd obviously have to retrieve the object's  
properties of interest to find out what, so it's not very precise. The  
demo's Object Inspector taps into this for example.

KVO is trickier. Unfortunately right now some of the most basic  
properties of a drawable are not KVC compliant (e.g. setting the  
object's position uses -moveToPoint: but retrieving it uses - 
location). This isn't so bad - I can add a -setLocation: method that  
the existing ones call for example. That's probably worth doing in  
general for the basic properties such as location, size, angle. I'd  
prefer this to adding individual notifications for every property  
because overall there are so many. Most properties of more specific  
classes are already KVC compliant, it's just these fundamental ones  
that aren't.

It worries me a bit that you want to use these notifications just to  
update a piece of userInfo data. That sounds like trying to  
synchronise two copies of the same data which is almost always a bad  
idea. Of course if you are simple *presenting* that data to the user  
somehow that's another matter.


cheers, Graham