Question

I’m trying to addobjects to a nsmutable array in lion, xcode 4.3 using ARC. the following is causing the program to crash with SIGABRT

 NSMutableArray *myArray = [NSMutableArray arrayWithCapacity:10];
 [myArray insertObject:@"Hello World" AtIndex:5]

how can i add custom objects to any index in the array?

Thanks in advance for your help.

Answer 1

If you want to use NSArray in the same manner of C fixed-size array, I suggest you fill the NSArray instance with as many [NSNull null] as you want for array size, e.g. 10 items in this case.

NSMutableArray *myArray = [NSMutableArray arrayWithCapacity:10];
for(int i = 0; i < 10; i++) {
    [myArray addObject:[NSNull null]];
}

And when you want to insert object, use replaceObjectAtIndex:withObject: instead. The size of the array won’t change.

[myArray replaceObjectAtIndex:5 withObject:@"Hello World"];

You also need to check against [NSNull null] when accessing item.

id item = [myArray objectAtIndex:5];
if (item != [NSNull null]) {
    NSString* stringItem = item;
    // your code here
}