I am using attach content control to upload multiple files to the work flow. So while uploading multiple files if the user selects same file more than one time a validation must be shown that particular file is repeated and he/she need to delete it.

But to do this I need to do something on the attach button provided by the attach content control and that is a final rule and to call any event actions on the attach content it is said that once the default behavior of attach content is completed then the even actions written on it will get triggered in this case it won't help to write some validation on the attach content.