Re: unrecognized selector error when calling -stringValue on NSNumber
Re: unrecognized selector error when calling -stringValue on NSNumber
- Subject: Re: unrecognized selector error when calling -stringValue on NSNumber
- From: Quincey Morris <email@hidden>
- Date: Sun, 6 Dec 2009 18:52:03 -0800
On Dec 6, 2009, at 15:58, Mazen M. Abdel-Rahman wrote:
> NSNumber * primaryLanguageNumber = [self primaryLanguageID];
> NSString * primaryLanguageString = [primaryLanguageNumber stringValue];
>
> primaryLanguageID is of type NSNumber. When I am stepping through the debugger I can see the variable primaryLanguageNumber being set correctly. However, once I try to call stringValue on it I get the following error:
>
> 2009-12-06 16:51:24.525 Averroes[21013:a0f] -[NSCFString stringValue]: unrecognized selector sent to instance 0x1001d8a70
>
> Doesn't that mean that it thinks primaryLanguageNumber is a string? And why would it see it as a string?
It's seeing it as a string because it *is* a string. That is precisely what the error message is telling you -- that the class of the receiver is NSCFString instead of whatever you intended it to be.
There's one fairly obvious scenario that causes this to happen. If you have a text field that modifies the primaryLanguageID property via a binding, and you edit the text field, then the new value will be a NSString regardless of whether the original value was a NSNumber (or anything else). If you want the modified property to be kept as a NSNumber, you must put a numeric formatter on the text field. (Or, if it's part of a table view, then you must put a numeric formatter on the column's text field cell.) (Or, write a setter for the primaryLanguageID property that takes a NSString parameter but stores a NSNumber in the instance variable.)
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