aid in the use of the replace list item

aid in the use of the replace list item

I'm trying to replace an item in a list with another list item replace
but something is wrong in the right direction, the error I get is:

list index too large

replace list item: attempt to replace item number 3 of a list of length 2:(1 to 2 Cancel)

some help?

check the length of the list before replacing an item

It would really help if you provided a screenshot of your relevant blocks, so we can see what you are trying to do, and where the problem may be.

here it is

how can I add the control to the length before adding the item?

if length of list > 1 then...

http://appinventor.mit.edu/explore/ai2/support/blocks/lists.html#lengthoflist

length of list

Returns the number of items in the list