On 5/7/08 6:16 PM, Dave Dribin said:
>In Interface Builder I bind the button's "Enabled" to
>"MyController.canEnableButton". The implementation for
>canEnableButton is this:
>
>- (BOOL)canEnableButton {
> NSArray * selectedPeople = [peopleController selectedObjects];
> if ([selectedPeople count] < 1)
> return NO;
>
> Person * selectedPerson = [selectedPeople objectAtIndex:0];
> return [selectedPerson.lastName hasPrefix: @"D"];
>}
>
>Of course, canEnableButton is now dependent on the selection of
>NSArrayController. Thus, I added this:
>
>+ (NSSet *)keyPathsForValuesAffectingCanEnableButton {
> return [NSSet setWithObjects:
>@"peopleController.selectionIndexes", nil];
>}
>
>However, this does not trigger the button to update when the selection
>changes.
Have you put a breakpoint in 'canEnableButton'? When
'peopleController.selectionIndexes' changes, do you hit the breakpoint?
I suspect not. The docs for keyPathsForValuesAffectingValueForKey say
keyPaths are ok, but mmalc has mentioned on this list "provided that the
path doesn't include to-many relationships". This appears to be true in
your case, so probably explains it. The docs don't mention this
caveat. :( However, I haven't got keypaths to trigger even with to-one
relationships, which I have been meaning to investigate...
>In observeValueForKeyPath:ofObject:change:context:
>
> if (context == SelectionIndexesContext)
> {
> [self willChangeValueForKey:@"canEnableButton"];
> [self didChangeValueForKey:@"canEnableButton"];
> }
>
>This works, however, it just seems wrong to use {will/
>did}ChangeValueForKey: like this.
Also, I seem to remember reading that doing willChange/didChange back-to-
back without actually changing anything is a no-no. You might check the
archives to confirm my shoddy memory.
--
____________________________________________________________
Sean McBride, B. Eng [EMAIL PROTECTED]
Rogue Research www.rogue-research.com
Mac Software Developer Montréal, Québec, Canada
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