System.ArgumentOutOfRangeException: 'Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')'

Question

I can't figure out why I'm getting this error, I spend like an hour looking at this code and nothing comes to my mind. " System.ArgumentOutOfRangeException: 'Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')' "

private void SetUpGame()
        {
            List<string> animalEmoji = new List<string>()
            {
                "", "",
                "", "",
                "", "",
                "", "",
                "", "",
                "","",
                "","",
                "","",
            };
            Random random = new Random();

            foreach (TextBlock textBlock in mainGrid.Children.OfType<TextBlock>())
            {
                int index = random.Next(animalEmoji.Count);
                string nextEmoji = animalEmoji[index];
                textBlock.Text = nextEmoji;
                animalEmoji.RemoveAt(index);
            }
        }

Which line throws the exception? What are the runtime values of the variables on that line when it happens? — David, Feb 16 '21 at 21:01
It trows on the "string nextEmoji = animalEmoji[index];" and I don't really know how to check runtime values — Pnukso, Feb 16 '21 at 21:03
How many `TextBlock` instances are returned by `mainGrid.Children.OfType()`? — Joshua Robinson, Feb 16 '21 at 21:03
@Pnukso: [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/q/25385173/328193) Failing the use of a debugger, you can also log/output useful information in some way so that you can observe the resulting logged output and see what information was written. — David, Feb 16 '21 at 21:05

score 0 · Accepted Answer · answered Feb 16 '21 at 21:03

If you have more textBlocks in mainGrid.Children.OfType<TextBlock>() than you have emojis you will hit a point where you're all out of emojis and cannot access the 0th item with string nextEmoji = animalEmoji[index]; - your empty list (Count of 0) causes random.Next(0) to return 0, which then cannot be used as a list indexer

https://dotnetfiddle.net/yYH9ta

System.ArgumentOutOfRangeException: 'Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')'

1 Answers1