[NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object

Question

UPDATED This is my code; the last line of code caused the error as described in the title. I understand userDefaults will always return an immutable object; so how do I fix this? I tried making the sending field a "mutable copy" but it was flagged as an error.

    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];

   if(textField.tag == kStaffName)  {  //  get index of staffName textField
    NSMutableArray *staffNamesArray = [[userDefaults arrayForKey:@"staffNamesArray"] mutableCopy];

    NSInteger indexSelected = [oStaffPickerView selectedRowInComponent:0];

    [staffNamesArray replaceObjectAtIndex:indexSelected withObject:textField.text];

@njzk2 Definitely not a duplicate: the code already uses `mutableCopy` and, thus, matches [the accepted answer](http://stackoverflow.com/a/5710719/11940). — Raphael Schweikert, Jan 21 '15 at 16:11
Since there is an "if" cleverly hidden beyond the right border of the screen, are you sure you are not modifying any other arrays that are still immutable? — gnasher729, Jan 21 '15 at 16:14
Question updated - sorry I didn't see the "cleverly hidden if statement"... it's fixed now. — SpokaneDude, Jan 21 '15 at 16:17
@njzk2: how about removing the downvote, if indeed it's your doing? Thanks... — SpokaneDude, Jan 21 '15 at 16:18
@njzk2: error was "bad receiver type" (mutableCopy was placed at end of statement) — SpokaneDude, Jan 21 '15 at 16:26
You can try this: NSMutableArray *staffNamesArray = [[NSMutableArray alloc] initWithArray:[[userDefaults arrayForKey:@"staffNamesArray"] mutableCopy]]; — weso, Jan 21 '15 at 16:27
Can you show the full stack trace. Have you added a breakpoint to verify the crash location and the array class? — Wain, Jan 21 '15 at 16:28
@spokane-dude: how about not assuming things, and adding the complete error log to your question? — njzk2, Jan 21 '15 at 16:29
@njzk2: Sorry about forgetting the stack trace... I uploaded it to pastBin... http://pastebin.com/40c5Sxc4 — SpokaneDude, Jan 21 '15 at 16:34
@weso: that looks good... I'll update my code and see if I can cause it to crash... when you have time, please rewrite your comment as an answer. — SpokaneDude, Jan 21 '15 at 16:36

score 1 · Accepted Answer · answered Jan 21 '15 at 16:38

1

You can try this:

NSMutableArray *staffNamesArray = [[NSMutableArray alloc] initWithArray:[userDefaults arrayForKey:@"staffNamesArray"]];

Hope this help you!

answered Jan 21 '15 at 16:38

weso

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you shouldn't need 2 mutable copies – Wain Jan 21 '15 at 16:40
It's true, is copy and paste. Edit mi response – weso Jan 21 '15 at 16:41
@Wain: *userDefaults* returns an immutable array, which I believe is the cause of the problem. So, wouldn't weso's code make the userDefaults array mutable? – SpokaneDude Jan 21 '15 at 16:49
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It was originally making a mutable copy and passing that to `initWithArray:` – Wain Jan 21 '15 at 16:50
@Wain I understand now... thanks for your help and I promise to do better when building my questions... :D – SpokaneDude Jan 21 '15 at 16:51

[NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object

1 Answers1