for循环没有正确返回索引

I have a for loop that I use to get the list item for displaying in my line graph. It's very simple but I get an index is out of range error. The way I understand what happens in the for loop is as long as the i is less then the indexCount() it keeps counting. Why is mine going past my index method? I have researched and used breakpoint found nothing and i = my collection size.I have a for loop that I use to get the list it