Strange Issue arising while removing object from NSMutableArray

Question

I am initializes NSMutableArray with 4 object.Then I am adding 2 more object in it after the first index. Then I am deleting that two new added objects. From theory it is clear that after all operation i will get the original array back that i have created first, but after deleting objects i am getting strange result.

CODE :-

- (void)viewDidLoad
{
    [super viewDidLoad];
   NSMutableArray *arr = [[NSMutableArray alloc]initWithObjects:@"1",@"2",@"3",@"4", nil];

    for (NSString *str in arr)
    {
        NSLog(@"%@",str);
    }

    [arr insertObject:@"1.1" atIndex:1];
    [arr insertObject:@"1.2" atIndex:2];

    for (NSString *str in arr)
    {
        NSLog(@"New %@",str);
    }

    [arr removeObjectAtIndex:1];
    [arr removeObjectAtIndex:2];

    for (NSString *str in arr)
    {
        NSLog(@"Old %@",str);
    }
}

OUTPUT :-

2013-12-28 14:42:02.703 ArrayDemo[1687:11303] 1
2013-12-28 14:42:02.704 ArrayDemo[1687:11303] 2
2013-12-28 14:42:02.705 ArrayDemo[1687:11303] 3
2013-12-28 14:42:02.705 ArrayDemo[1687:11303] 4
2013-12-28 14:42:02.705 ArrayDemo[1687:11303] New 1
2013-12-28 14:42:02.706 ArrayDemo[1687:11303] New 1.1
2013-12-28 14:42:02.706 ArrayDemo[1687:11303] New 1.2
2013-12-28 14:42:02.706 ArrayDemo[1687:11303] New 2
2013-12-28 14:42:02.707 ArrayDemo[1687:11303] New 3
2013-12-28 14:42:02.707 ArrayDemo[1687:11303] New 4
2013-12-28 14:42:02.708 ArrayDemo[1687:11303] Old 1
2013-12-28 14:42:02.708 ArrayDemo[1687:11303] Old 1.2
2013-12-28 14:42:02.709 ArrayDemo[1687:11303] Old 3
2013-12-28 14:42:02.710 ArrayDemo[1687:11303] Old 4

I am not able to understand why this happening ??? Do anyone knows about it ?? Any help will be appreciated...

Thanks in advance....

Martin R · Accepted Answer · 2013-12-28 09:23:10Z

2

Initial array:

    1, 2, 3, 4

After [arr insertObject:@"1.1" atIndex:1]:

    1, 1.1, 2, 3, 4

After [arr insertObject:@"1.2" atIndex:2]:

    1, 1.1, 1.2, 2, 3, 4

After [arr removeObjectAtIndex:1]:

    1, 1.2, 2, 3, 4

After [arr removeObjectAtIndex:2]

    1, 1.2, 3, 4

So everything is correct. If you want to remove the elements that you inserted earlier, then you have to remove them in reverse order:

[arr removeObjectAtIndex:2];
[arr removeObjectAtIndex:1];

In this case, the final result would be 1, 2, 3, 4 again.

answered Dec 28, 2013 at 9:23

Martin R

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