It's a thing i made while learning flutter/dart, and i spent so much time on it so i'm way too proud not to publish it
As you can see on the actual tutorial, i wasn't actually meant to do more than add a delete button, but i did! and i'm proud of that!
Honestly, i have no idea, but i'm pretty sure you just need to flutter pub get
and then it should work fine, i guess you probably also need to point your IDE (Android Studio, in my case) to your Flutter SDK