Modify NSError localizedDescription

Question

Do you guys know if there is a nice way to set/modify a NSError's localizedDescription after it has been instantiated other than recreating it? I didn't find any.

Answer 1

NSError declares no setters for its properties. From this you can deduce that it probably is not meant to be modified after it has been created. I could see writing a category on NSError that would create an error out of another error but with a different value for the NSLocalizedDescriptionKey key.

Answer 2

The NSError class is - like many Cocoa classes - immutable.

However, the doc states for -localizedDescription that:

By default this method returns the object in the user info dictionary for the key NSLocalizedDescriptionKey. If the user info dictionary doesn’t contain a value for NSLocalizedDescriptionKey, a default string is constructed from the domain and code.

So just use errorWithDomain:code:userInfo: to create a new instance or copy and supply an appropriate user info.

Here's another nice introduction to the NSError class.

Answer 3

If you create your NSError manually specifying the userInfo, then you can rewrite this dictionary's value for key NSLocalizedDescriptionKey. Just cast error.userInfo to NSMutableDictionary or whichever class you used when created NSError object