What are keys and how do you use them?

A set of IDs for Widgets, Elements and SemanticsNodes make up the key class. Keys are responsible for preserving the state of widgets when they are updated inside the widget tree. Keys may also be used to modify and rearrange collections of widgets of the same type and defined states.

Otherwise, keys may be superfluous to the code, even if they aren’t harmful in any manner. Keys are useful when you need to edit a widget tree with stateful widgets, but not when the tree is entirely made up of stateless widgets.