NSMutableArray removeObjectAtIndex, but then I need to move down

Question

All,

I have strings stored in a NSMutableArray. When a certain condition is met elsewhere in the code, the object that is FIRST in the NSMutableArray (read, objectAtIndex:0) gets removed. After it is removed, I need to shift everything down an index. Here is my example:

/*
    Index/Value
    0 - one
    1 - two
    2 - three
    3 - four
    4 - five
    5 - six
    6 - seven
*/
//removes object...
[mArray removeObjectAtIndex:0];
//I am missing something here...


//I want the value of the array to be as follows:
/*
    Index/Value
    0 - two
    1 - three
    2 - four
    3 - five
    4 - six
    5 - seven
*/

What am I missing?

EDIT: The NSMutableArray is stored in NSUserDefaults. Is that what may be causing this not to work?

EDIT2: Because it is stored in NSUserDefaults, it changes to immutable. Check out the accepted answer for the correct way to do it. Details here: crashes my app [NSMutableArray1 removeAllObjects] iphone sdk

omz · Accepted Answer · 2011-07-11 19:16:21Z

7

You're not missing anything. The indexes will be exactly like that after removing the object at index 0.

answered Jul 11, 2011 at 19:16

omz

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10 Comments

Baub Over a year ago

I thought this was the case, but it throws an error "*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'" Maybe I have something wrong somewhere else in my code.

Joe Over a year ago

That is because you do not have a mutable array. mArray needs to be an NSMutableArray either by creating a new one or calling mutableCopy (which will return a retained copy) on an existing array.

Nate Thorn Over a year ago

@James That error means that your array is actually a normal NSArray, not an NSMutableArray. Check the place you initialize your array to make sure it's really being created as an NSMutableArray.

Joe Over a year ago

NSUserDefaults always returns an immutable array. Although you are setting it to mutable it will return immutable so when get the value back also call mutableCopy.

David Snabel-Caunt Over a year ago

The moral of this story is always post all relevant code, especially variable initialization. If Joe is correct, his comment should be added as an answer.

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Paul.s · Accepted Answer · 2011-07-11 19:45:39Z

6

If I understand your issue correctly you are storing an NSMutableArray to NSUserDefaults and then when you load it out of NSUserDefaults it throws an error when you try to mutate?

This is because when you retrieve the array from NSUserDefaults it will be an instance NSArray not NSMutableArray therefore you need to make a an instance of NSMutableArray to work with.

NSMutableArray *mArray = [[NSMutableArray alloc] initWithArray:myArrayFromNSUserDefaults];

answered Jul 11, 2011 at 19:45

Paul.s

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1 Comment

Baub Over a year ago

This worked perfectly. I also found an answer here as well for those who may stop by later: stackoverflow.com/questions/3955969/…

Mikael · Accepted Answer · 2011-07-11 19:22:17Z

0

That should work. Are you doing something like this?

    NSMutableArray *mArray = [[NSMutableArray alloc]init];
    [mArray addObject:@"one"];
    [mArray addObject:@"two"];
    [mArray addObject:@"three"];

    [mArray removeObjectAtIndex:0];

    NSLog(@"mArray at 0: %@",[mArray objectAtIndex:0]);

answered Jul 11, 2011 at 19:22

Mikael

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