insert object in an NSMutableArray saved with NSUserDefaults

Question

I have an NSMutableArray saved with NSUserDefaults. This array is my "favourite" items that the user can saves, so when i want to add one item, i need to read the array (from NSuserDefault) and save in the first free position.

I'm using this method to add a value in the NSMutableArray

-(IBAction)save{
   NSMutableArray *abc = [[NSUserDefaults standardUserDefaults] objectForKey:@"12345"];
   int n = [abc count];
   [abc insertObject:@"aaa" atIndex:n];
   NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
   [[NSUserDefaults standardUserDefaults] setObject:abc forKey:@"12345"];
   [defaults synchronize];
   [abc release];
}

what's the deal? That if the user call this method two times, the second time the app crashes with this log:

* Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object'

why? and why just the second time? The first time works fine!

score 35 · Accepted Answer · edited Jul 02 '17 at 03:13

35

NSUserDefaults always returns immutable objects, even if the original object was mutable. It's in the documentation for objectForKey:

The returned object is immutable, even if the value you originally set was mutable.

You will need to create a copy of the returned object before you modify it, using [NSMutableArray arrayWithArray:]

Probably also best to use the arrayForKey method of NSUserDefaults if you're retrieving an array. Docs here: https://developer.apple.com/documentation/foundation/userdefaults

edited Jul 02 '17 at 03:13

Cœur

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answered Mar 17 '11 at 23:23

lxt

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right! :) `NSMutableArray *bbb = [[NSMutableArray alloc] initWithArray:abc];` works! thanks! – JAA Mar 17 '11 at 23:26
6

@JJSaccolo: A shortcut you can take is `NSMutableArray *bbb = [abc mutableCopy];`. – dreamlax Mar 18 '11 at 00:54

score 9 · Answer 2 · answered Dec 06 '13 at 04:05

Here is a complete working example:

- (void)saveScore:(NSNumber *)score
{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    NSMutableArray *scoreList = [[NSMutableArray alloc] initWithArray: [defaults objectForKey:@"ScoreList"]];
    [scoreList addObject:score];
    [defaults setObject:scoreList forKey:@"ScoreList"];
    [defaults synchronize];
}

First we read in the stored data in a mutable array, update the array, save the new array, and then synchronize the user defaults to permanently record the changes.

Hope this helps!

I'm guessing you would retrieve it like.. NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults]; NSMutableArray *array = [userDefaults objectForKey:@"arraySaveData"]; _mutableArray=array; — Seb OH, Mar 01 '14 at 07:01

score 1 · Answer 3 · answered May 18 '12 at 17:09

1

Another option is:

[[NSUserDefaults standardUserDefaults] setObject:[[[NSUserDefaults standardUserDefaults] objectForKey:@"12345"] arrayByAddingObject:object] forKey:@"12345"];

answered May 18 '12 at 17:09

RileyE

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score 1 · Answer 4 · edited Apr 17 '14 at 09:32

1

Copy Array from an NSUserDefault like this way :

[YourArray addObjectsFromArray:[[NSUserDefaults standardUserDefaults] 
                  objectForKey:@"NSUSD"]];

or

YourArray = [[NSMutableArray alloc] 
             initWithArray:[[NSUserDefaults standardUserDefaults]  
              objectForKey:@"NSUSD"]];
[YourArray addObject: (currentObject)];

edited Apr 17 '14 at 09:32

Alex Cio

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answered Dec 07 '12 at 07:29

Amitabha

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score 0 · Answer 5 · answered Mar 11 '14 at 01:44

0

Quick fix:

_retrivedArray = [_mutableArray mutableCopy];

answered Mar 11 '14 at 01:44

Seb OH

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score 0 · Answer 6 · answered Mar 17 '11 at 23:28

It is because you NSMutablepointer points an NSUserDefault object directly. You should first copy NSUserDefault object to an array than process it.

NSMutableArray *arr= [NSMutableArray arrayWithObjects:@"asd",@"dsa",nil];
    [[NSUserDefaults standardUserDefaults] setObject:arr forKey:@"12345"];
NSMutableArray *abc = [NSMutableArray arrayWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:@"12345"]];
//[[NSUserDefaults standardUserDefaults] objectForKey:@"12345"];
    int n = [abc count];
    [abc insertObject:@"aaa" atIndex:n];
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [[NSUserDefaults standardUserDefaults] setObject:abc forKey:@"12345"];
    [defaults synchronize];
    [abc release];

insert object in an NSMutableArray saved with NSUserDefaults

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