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Editorial Team
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Asked: 2026-06-01T17:11:03+00:00

I have an NSMutableDictionary with keys and values set up initially. Later I need

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I have an NSMutableDictionary with keys and values set up initially.
Later I need to update the values for certain keys, and I thought I would just need to do
[mutableDict setValue:val forKey:key], but this throws an exception saying: 

[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object

What am I doing wrong?
(I have another mutable dictionary inside each key of the mutable dictionary, but I don’t think that’s why)

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1 Answer

  1. Editorial Team

    I’ll copy an paste my comment just incase you want to keep your 100% accept

    Paul.s

    For some reason you are actually working with an NSDictionary not an NSMutableDictionary. Hard to say why without more code, maybe you are using a copy obtained by calling copy or you have loaded the dictionary from a plist/userDefaults.. Can we see some more code?

    Dennis

    @Paul.s Yes, I did copy an NSMutableDictionary. Would that be why? If it is, then what else should I use to copy?

    Paul.s

    Use mutableCopy instead of copy to get a mutable dictionary

    Dennis

    @Paul.s oh.. didn’t know about that. I’m new to Objective-C and I tried to search for what I am doing wrong but I missed it 🙁 Thank you!!

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