title: how to enable button when button already changed in swift
body: <p>so i have 3 buttons.
  the first one for take a picture/pick image from gallery
  the second one for take an autograph and segue it to another view controller
  the last one is the next button</p>
  
  <p>i want to disable my next button if the user have not full fill the image and the signature.And enable the button if user already full fill the image and the signature</p>