Concatinate two values from two drop down list and populate the value in a text box

Hi,

I want to concatinate two values from two drop down lists and populate the new value in a text box.

When I applied the below rule 

"When dropdownlist1 is changed

if an advanced condition is true (dropdownlist1 equals value and dropdownlist2 has a value)

the transfer data Expression (Concatinate dropdownlist1, dropdownlist2)"

Only the value from dropdownlist1 is populating in the text box.

But when I give the same expression directly in the text box property it will populate both the values while execution.

Please help me to complete this.

Thanks in advance.

Regards,

Abin K Thomas