On Aug 31, 2008, at 6:38 PM, Jamie Phelps wrote:
I have an NSPopUpButton with five menu items: WTD, MTD, QTD, YTD,
and Specific Dates. What I want to do is show and hide two labels
and textfields for Start Date and End Date depending on if the
Specific Dates option is selected.
My first attempt was to do
@property (readonly) BOOL specifyingDateRange;
-(BOOL)specifyingDateRange{
if([dateRangePopUp indexOfSelectedItem] == 4){
return YES;
}
return NO;
}
but this is not working correctly.
Can anyone explain what the correct implementation is and possibly
what mistake I made in assessing the problem?
It's hard to know without more details.
My suspicion is that you haven't arranged for any KVO change
notification to be sent out when this property changes its value. KVO
and Bindings do not poll the properties of objects to check if they've
changed. There has to be an affirmative notification sent out to
observers telling them that the property may have changed. That
notification is triggered by a message to the object which has the
property -- either a KVO-compliant setter (preferred) or a pair of
willChange…/didChange… messages (last resort if your design
absolutely can't conform to the normal way of doing things).
I assume the above method is in your controller. It certainly
shouldn't be in the model. However, is the mode implied by the pop-up
expressed in the model? And is the pop-up's selection bound through
the controller to that model property? If so, then I'd recode that
method to depend on the model property instead of the pop-up view's
state. And then I'd use a
+keyPathsForValuesAffectingSpecifyingDateRange method to inform KVO
that when the model property changes, that implies a change in the
specifyingDateRange property of the controller.
If somehow the mode implied by the pop-up isn't a model property, then
I'd make it a controller property. You'd still bind the pop-up's
selection to it, and you'd still use
+keyPathsForValuesAffectingSpecifyingDateRange to inform the KVO
system that the two properties are interrelated.
Cheers,
Ken_______________________________________________
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