Re: Force redisplay of NSTextField after NSFormatter subclass change

FROM : Matt Neuburg
DATE : Tue Nov 27 19:10:49 2007

On Tue, 27 Nov 2007 16:27:23 +0000, Jonathan Fewtrell
<<email_removed>> said:
>I have an NSTextField bound to a certain key in a Core Data model
>entity. A switch in the interface allows the user to display the
>value in either of two formats. The formats are quite different, so I
>have two different NSFormatter subclasses and I set the appropriate
>one when the user toggles the switch. I find that the displayed value
>immediately after a switch is spurious, So I want to force the field
>to redisplay. Nothing I try seems to get it to redisplay. I have
>tried the following:
>
>sending -setNeedsDisplay: to the field
>sending -display to the field
>setting the field hidden and then unhidden
>sending a -willChangeValueForKey: / -didChangeValueForKey; pair to
>the model object
>
>It appears that because the underlying value of the key (which is an
>NSNumber) does not change, the field refuses to update. The only way
>I can get it to work is to change the value of the key and change it
>back again. But this seems a clumsy hack. Is there a better way?


This answer has nothing to do with Core Data - I experience the same
difficulty *any* time I change NSFormatters in the middle of the app's
lifetime. My solution is: when I change the formatter, I also manually pass
the current value being used as the source of the textfield's text thru the
formatter:

NSString* s = [self valueForKey:@"filenameSearch"];
[myTextField setFormatter: (newMode ? f : nil)];
if (newMode) {
  id val;
  if ([f getObjectValue:&val forString:s errorDescription:nil])
    [self setValue:val forKey:@"filenameSearch"];

My ivar "filenameSearch" is bound from the textfield, so capturing that
value before the formatter change and then passing it thru the formatter
after the change and resetting it in a KVO-compliant way causes the right
thing to appear in the field.

This sounds a lot like what you're already doing, unfortunately... :)

m.
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