How to fix Flutter error: "Type 'Item' not found."

This code has been working for several weeks, but suddenly brought up errors after an AndroidStudio update:

    class _GameState extends State<Game> {
  List<Item> its = [
    Item('fins','images/idea-fins.png'),
    Item('sonar','images/idea-sonar.png'),
    Item('suction','images/idea-suction.png'),
    Item('tires','images/idea-tire.png'),
    Item('velcro','images/idea-velcro.png'),
    Item('propeller','images/idea-propeller.png')
  ];

The error I get is:

    Error: Type 'Item' not found.
  List<Item> its = [

Does "Item" now have to be defined, somehow, or has some more fundamental change been made?

Added this near the beginning and now it works:

class Item {
  String name="";
  bool dropped=false;
  String pic="";

  Item(String a, String b)
  {
    name =a;
    pic =b;
  }
}