mutating method sent to immutable object

Question

When I use this method first time it works fine, but when I called it second time I get the error "mutating method sent to immutable object". The problem is at line with "addObject" command.

-(IBAction) save: (id) sender{

NSMutableArray *placesT= [[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"];

if (!placesT) {
    placesT=[[[NSMutableArray alloc] init] autorelease];
}

[placesT addObject: [NSString stringWithFormat:@"%@", tagF.text] ];

NSUserDefaults *tUD=[NSUserDefaults standardUserDefaults];
[tUD setObject:placesT forKey:@"placesT"];
[tUD synchronize];

[self dismissModalViewControllerAnimated:YES];

}

Well the problem is with the placesT initialization. My bet is the NSUserDefault standard is empty the first time and goes to the second init. You also have a memory leak ther. — Radu, Apr 26 '11 at 13:06
Note that you can probably replace `[NSString stringWithFormat:@"%@", tagF.text]` with `tagF.text` only. There’s no need to send `+stringWithFormat:` if `text` is already an `NSString`. — , Apr 26 '11 at 23:21

score 24 · Answer 1 · answered Apr 26 '11 at 13:05

24

As the documentation for NSUserDefaults says: "Values returned from NSUserDefaults are immutable, even if you set a mutable object as the value." Whenever you want to change a collection you get from NSUserDefaults you have to get the immutable version, make a mutableCopy, modify that, and set it back again.

answered Apr 26 '11 at 13:05

smorgan

20,228
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2

to add to this that would be for example: someMutableArray = [yourArrayFromDictionary mutableCopy]; hope that helped :) – jimbob Jan 04 '13 at 02:03

score 10 · Answer 2 · edited Aug 05 '13 at 10:51

That is because the object stored in the NSUserDefaults is not the mutableArray but a normal array.

- (IBAction)save:(id)sender {

   NSMutableArray *placesT = nil;
   NSArray *tempArray = [[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"];

   if (tempArray) {
      placesT = [tempArray mutableCopy];
   } else {
      placesT = [[NSMutableArray alloc] init];
   }

   [placesT addObject:[NSString stringWithFormat:@"%@", tagF.text]];

   NSUserDefaults *tUD = [NSUserDefaults standardUserDefaults];
   [tUD setObject:placesT forKey:@"placesT"];
   [tUD synchronize];

   [self dismissModalViewControllerAnimated:YES];
   [placesT release];
}

score 3 · Answer 3 · edited Apr 18 '15 at 17:16

3

placesT is a non mutable array, either always set placesT a mutable object always or use following code.

NSMutableArray *placesT= [[[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"] mutableCopy];

edited Apr 18 '15 at 17:16

Marco Bonelli

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answered Apr 18 '13 at 12:38

Amit Battan

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score 0 · Answer 4 · answered Nov 18 '14 at 08:18

This should work:

-(IBAction) save: (id) sender {

NSMutableArray *placesT= [[NSMutableArray alloc]initWithArray:[[NSUserDefaults standardUserDefaults]

objectForKey:@"placesT"]];

if (!placesT) {
    placesT=[[[NSMutableArray alloc] init] autorelease];
}

[placesT addObject: [NSString stringWithFormat:@"%@", tagF.text] ];

NSUserDefaults *tUD=[NSUserDefaults standardUserDefaults];
[tUD setObject:placesT forKey:@"placesT"];
[tUD synchronize];

[self dismissModalViewControllerAnimated:YES]; }

mutating method sent to immutable object

4 Answers4

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