Learn more at the following links,
many of which have been contributed by the Flutter community:

General overview

Things to review before selecting an approach.

Introduction to state management,
which is the beginning of this very section
(for those of you who arrived directly to this Options page 
and missed the previous pages)

Pragmatic State Management in Flutter,
a video from Google I/O 2019

Flutter Architecture Samples, by Brian Egan

Provider

Simple app state management, the previous page in this section

Provider package

Riverpod

Riverpod, another good choice, is
similar to Provider and is compile-safe and testable.
Riverpod doesn’t have a dependency on the Flutter SDK.

Riverpod homepage

Getting started with Riverpod

setState