How to add an imageView to collectionView as background

• What are the three ways to track where is the user from?
  • Idfa and cookie
  • Google play url
  • Common info
    • Device id
    • Mac address
    • IP address
    • Device name
    • Wifi mac address
    • Region
    • Local
• How to add a view to collectionView’s background and send to back?
  • The view should be userInteractive set to false
  • Add it as subview
  • Send back
  • Make layer’s zposition to negative value
• How to set substring’s attributes for an attributes string?
  • In SwifAttributed string, get range of substring, check if it is NSNotfound
  • If not, set(style: forRange:)