Accessing NSString within NSMutableArray

Question

Why can I not access the 4th element of an NSMutableArray when I initialise with a NSString object rather than input the text manually?

For Example:

NSString * d = @"d";

self.arr = [[NSMutableArray alloc] initWithObjects:
          [NSMutableArray arrayWithObjects:@"A",@"B",@"C",d,nil],
          [NSMutableArray arrayWithObjects:@"A",@"B",@"C",@"d",nil],
           nil];

This causes a beyond bounds error (NSString):

NSMutableArray *subArray  = [self.arr objectAtIndex:0];
question = [subArray objectAtIndex:3];

This doesn't (@"d"):

NSMutableArray *subArray  = [self.arr objectAtIndex:1];
question = [subArray objectAtIndex:3];

Why does this happen? Surely they are the same thing? I was hoping to reduce the amount of times I would have to write @"d".

have you try with NSLog(@"%@",[[self.arr firstObject ]objectAtIndex:3]); — Toseef Khilji
– Toseef Khilji, Commented Dec 16, 2013 at 9:03
Is this for a quiz type of app? There are other ways you can store the answers. — Stephen J
– Stephen J, Commented Dec 16, 2013 at 9:04
This code looks good to me. One thing to try is to log the whole array and see if it's what you expect (NSLog(@"%@", self.arr)). It's possible that d isn't really set to what you think it is, and it's in fact nil at the time of array creation. — cobbal
– cobbal, Commented Dec 16, 2013 at 9:07

chancyWu · Accepted Answer · 2013-12-16 09:06:40Z

1

They should be same... i tried following in my project. it works well.

NSString * d = @"d";

NSMutableArray *array = [[NSMutableArray alloc] initWithObjects:
                [NSMutableArray arrayWithObjects:@"A",@"B",@"C",d,nil],
                [NSMutableArray arrayWithObjects:@"A",@"B",@"C",@"d",nil],
                nil];

NSLog(@"0 array 4th:%@",[[array objectAtIndex:0] objectAtIndex:3]);
NSLog(@"1 array 4th:%@",[[array objectAtIndex:1] objectAtIndex:3]);

output is as followings:

2013-12-16 17:05:30.092 Demo[1005:60b] 0 array 4th:d
2013-12-16 17:05:30.094 Demo[1005:60b] 1 array 4th:d

answered Dec 16, 2013 at 9:06

chancyWu

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