3. Provide an optional action

You might want to provide an action to the user when
the SnackBar is displayed.
For example, if the user accidentally deletes a message,
they might use an optional action in the SnackBar to recover
the message.

Here’s an example of providing
an additional action to the SnackBar widget:

Interactive example

Note:
  In this example, the SnackBar displays when a user taps a button.
  For more information on working with user input,
  see the Gestures section of the cookbook.

Add a drawer to a screen

Export fonts from a package