_formProgress == 1 ? _showWelcomeScreen : null


    This is a Dart conditional assignment and has the syntax:
condition ? expression1 : expression2.
If the expression _formProgress == 1 is true, the entire expression results
in the value on the left hand side of the :, which is the
_showWelcomeScreen method in this case.

Step 2.5: Launch Dart DevTools

How do you debug a Flutter web app?
It’s not too different from debugging any Flutter app.
You want to use Dart DevTools!
(Not to be confused with Chrome DevTools.)

Our app currently has no bugs, but let’s check it out anyway.
The following instructions for launching DevTools applies to any workflow,
but there is a short cut if you’re using IntelliJ.
See the tip at the end of this section for more information.