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Editorial Team
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Asked: 2026-05-16T02:09:54+00:00

I have some trouble with a core data project. I have a NSArrayController with

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I have some trouble with a core data project. I have a NSArrayController with NSManagedObjects in it, and + / – buttons. If i delete a object in the row after the file has been saved it works perfectly, but if I add a new object, and immediately delete it again (without changing any of the default values), i get an error: 

Serious application error.  Exception was caught during Core Data change processing: Unknown number type or nil passed to arithmetic function expression. with userInfo (null)  
Unknown number type or nil passed to arithmetic function expression.

It’s the same case if i undo the add of the new object.

Anybody able to give me a pointer what to do? I assume it has something to do with that it only has an temporary ID, but how to solve it i don’t know.

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1 Answer

  1. Editorial Team

    I found the problem and solution. For the record i will describe it.

    The problem was that the object in its init function added an observer on itself. This was probably what triggered the error. If i before i delete the object remove itself as observer, the error is not produced.

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