Re: NSFormatter interfering with bindings continuous update?

FROM : Lee Ann Rucker
DATE : Tue Jun 26 00:40:57 2007

Funny you should ask; I was just working on the exact same problem, 
and having the same results.

Hit google and found that in http://developer.apple.com/documentation/
Cocoa/Conceptual/CocoaBindings/Concepts/MessageFlow.html


12. If the view has an NSFormatter attached to it, the value is 
formatted by the NSFormatter instance. Proceed to Step 17.
13. If the controller-model binding specifies a value transformer the 
entire model is transformed using the transformedValue: method.
14.The controller generates a key-value observing message, mapping 
the key path to the selection. This generates the same type of key-
value observing change notification that would result in replacing 
the content object. Proceed to Step 7.
15.If the binding specifies a placeholder for the view-controller 
binding for the value marker it is used in Step 16. If no custom 
placeholder value is specified as part of the binding, and a custom 
default placeholder has been set for the view class and this 
particular binding, it is used in Step 16. Otherwise, flow returns to 
Step 11.
.An application can assign a custom default placeholder for a class 
and binding combination using the NSPlaceholders class method 
setDefaultPlaceholder:forMarker:withBinding:.
16.The placeholder value is set for the view using the 
setPlaceholderString: or setPlaceholderAttributedString: method.
17. The updated value is displayed in the user interface.

So it looks like it's intentionally skipping the steps we want. This 
is very annoying. I tried NSValueTransformer, but adding that to an 
editable NSTextField makes it non-editable.


On Jun 21, 2007, at 3:25 AM, Joe Wildish wrote:

> All,
>
> I have a custom subclass of NSFormatter attached to an NSTextField 
> (done programmatically). The text field is bound and configured to 
> "Continuously Update Values". The behaviour I am getting is that 
> the first time a change is made to the field, the setter method 
> gets called as you would expect. However, all subsequent changes to 
> the field do not trigger the setter method - the next time it is 
> called is when focus is moved away from the control.
>
> My formatter isn't doing too much, but I stripped it down to the 
> bare minimum anyway:
>
> - (NSString *)stringForObjectValue:(id)obj {
>     return [NSString stringWithString:obj];
> }
>
> - (BOOL)getObjectValue:(id *)obj forString:(NSString *)string 
> errorDescription:(NSString **)error {
>     * obj = [NSString stringWithString:string];
>     return YES;
> }
>
> Even with this formatter, the behaviour is still as described. If I 
> *don't* attach the formatter, the binding works as you would 
> expect. I would be grateful if someone might be able to point out 
> what I'm doing wrong.
>
> Cheers,
> -Joe
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