How to prevent counting an empty NSMutableArray

Question

Hi,

I would like to simulate the SMS Bubbles of the iPhone for my own app. I found some nice code overhere (FYI): http://vimeo.com/8718829 . It is a restyled UITableView. Exactly what a wanted.

Here is the problem: - The Tableview is filled with an array of messages - It needs to be a NSMutable array because you want to add messages on the fly. - When there are no messages yet, the message-array is empty. - But counting an empty NSMutableArray causes an exeception, the app crashes. (you need the count for scrolling).

So what is a nice solution for that? I now pre fill the array with "". But that is very ugly. You see a mini bubble on the screen.

Can you hide cells? In the example on the video, there are already 2 messages so the problem does no occur.

Any suggestion is welcome. Tnx Christian

Answer 1

Actually counting an empty array does not raise any exception. I think the problem is here:

- (void)add {
    if(![field.text isEqualToString:@""])
    {
        [messages addObject:field.text];
        [tbl reloadData];
        NSUInteger index = [messages count] - 1;
        [tbl scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:index inSection:0] atScrollPosition:UITableViewScrollPositionBottom animated:YES];

        field.text = @"";
    }
}

As the "-1" index cannot exist. You can edit that line to

        NSUInteger index = MAX(0, [messages count] - 1);

And it should work.

Answer 2

You can count an empty array (I assume you mean [arrayName count]) as long as its alloc'd so make sure its initialized somewhere earlier.