Objective-C accessing / changing array elements in a multidimensional array (NSArray)

Question

I'm trying to change a value in a multidimensional array but getting a compiler error:

warning: passing argument 2 of 'setValue:forKey:' makes pointer from integer without a cast

This is my content array:

NSArray *tableContent = [[NSArray alloc] initWithObjects:
                [[NSArray alloc] initWithObjects:@"a",@"b",@"c",nil],
                [[NSArray alloc] initWithObjects:@"d",@"e",@"f",nil],
                [[NSArray alloc] initWithObjects:@"g",@"h",@"i",nil],
                 nil];

This is how I'm trying to change the value:

[[tableContent objectAtIndex:0] setValue:@"new value" forKey:1];

Solution:

 [[tableContent objectAtIndex:0] setValue:@"new val" forKey:@"1"];

So the array key is a string type - kinda strange but good to know.

Answer 1

You're creating immutable arrays, and trying to change the values stored in them. Use NSMutableArray instead.

Answer 2

You want either NSMutableArray's insertObject:atIndex: or replaceObjectAtIndex:withObject: (the former will push the existing element back if one already exists, while the latter will replace it but doesn't work for indices that aren't already occupied). The message setValue:forKey: takes a value type for its first argument and an NSString for its second. You're passing an integer rather than an NSString, which is never valid.

Answer 3

NSMutableArray *tableContent = [[NSMutableArray alloc] initWithObjects:
                    [NSMutableArray arrayWithObjects:@"a",@"b",@"c",nil],
                    [NSMutableArray arrayWithObjects:@"d",@"e",@"f",nil],
                    [NSMutableArray arrayWithObjects:@"g",@"h",@"i",nil],
                     nil];

[[tableContent objectAtIndex:0] replaceObjectAtIndex:1 withObject:@"new object"];

You don't want to alloc+init for the sub-arrays because the retain count of the sub-arrays will be too high (+1 for the alloc, then +1 again as it is inserted into the outer array).