mutating method sent to immutable object

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];

}

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  • 4 Solutions Collect From Internet About “mutating method sent to immutable object”

    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.

    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];
    }
    

    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];
    

    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]; }