barrierDismissible property
Whether you can dismiss this route by tapping the modal barrier. The modal barrier is the scrim that is rendered behind each route, which generally prevents the user from interacting with the route below the current route, and normally partially obscures such routes.
For example, when a dialog is on the screen, the page below the dialog is usually darkened by the modal barrier. If barrierDismissible is true, then tapping this barrier will cause the current route to be popped with null as the value.
Implementation
final bool barrierDismissible;