How to make a dynamic list where user are prompted to enter text in a Text Form Field and the entered text can be accessed in a list?

I'm trying to create a page in a Flutter app where the user can enter input, let's say a Username. The entered username will then be updated to a list that the user can see. It almost works like "Favorites" feature, where a user adds into a Favorites List what they like most.

The only difference between my intended program and a Favorites List is that a Favorites List has all the entries listed in a list view already and the user just need to click the "Heart" button to added to the Favorites List.

My program, on the other hand, is intended to have the user Enter the input THEN click on a '+' button to add the entered entry into a Favorites List.

I hope this is clear enough of what I intend to do. Thank you.