Upload an attachment dynamically in SoapUI

Hi,

I need to upload the attachments dynamically to a request while running the automation. I have to attach different files to each request. 

Example: For the first run it should pickup file1 and for second run it should pickup file2 and so on... I have to test all the filetypes. So, i want to run that particular test cases for multiple times and file should be different for each time.

Could any one please help me to achieve this.