Hi Amar,

Maybe something similar to this?

you can set this on a data label and add a rule to check the vlaue of the data label

now if the dropdown has X, the expression will return True or False otherwise it will return the value of the textbox because the drop down list value is not X

I would add the following rule to validate the user entry when the value is changed in the textbox

When textbox is changed

If Data label equals false

Inform the user that the value doesn't match the pattern

This depends on your requirements, What I mean is that you can workaround this using expressions.

Hope it helps