Flutter State Management with rx_dart
This repo shows a very basic example of state management utilizing BehaviorSubjects from rx_dart.
How
State Class
Create a state class with a BehaviorSubject with the type of your state. Use BehaviorSubject.seeded() to add an initial value. Inside this state class, add all function which can mutate the state. Take any arguments in the function & do whatever manipulation and database calls are necessary, then add the new state to the stream.
Subscribe to State
In order to listen to the state, create a stateful widget. In the initState method, add a listener to the stream (BehaviorSubject) of the state. Inside this listener, you will receive an event (state) everytime the stream emits a new value. Use this value to change the widgets variables and call setState.
Why use a BehaviorSubject instead of a regular Stream?
The advantage of using rx_dart's BehaviorSubject is that we can access the last emitted value at any point in time, instead of only receiving events while subscribed. This means, a widget can subscribe to a state at any point in time, and get the current value as well as receive any values from this point forward.
Pro and Contra
Like any other state management solution, there are some advantages as well as disadvantages to this approach.
Advantages:
Clean build method
No additional widgets are needed in order to listen to the state. This means, for example, no Consumers. The only thing needed to get it to run is a stateful widget. This means that this state management solution keeps the build method free of any boilerplate and easy to read.
Reliability and Understandability
Nothing complicated is happening that you don't know about. You add events to the stream and you listen to the stream, simple as that.
Full Control
When subscribing to the stream inside the widget, you get to decide how to handle this specific event in this specific widget. The counter in this example always calls setsState for any new state, but this must not necessarily be the case for all widgets. A hypothetical widget displaying only if the counter is positive or negative might only call setState if the counter has changed from positive to negative.
Disadvantages
Boilerplate
Like every other state management solution, this also introduces some boilerplate code. While removing it from the widget tree, a function for subscribing to the state has to be added, as well as the widget itself has to be stateful.
Streams
A basic understanding of streams is needed in order to understand how this approach works.
No Documentation
Since this not necessarily a wide-spread approach, there is no documentation about this available, like for BLoC or Riverpod. But since the approach is so simple, with an understanding of this example and some slight changes, all use cases can easily be handled.
Changes to use in real world projects
- If needed, give the state object a variable which holds the "app state" of this state, like Ok, Request, and Error and change accordingly in state mutations like in 'increaseCounter'.
- Instead of making the state a global state with the singleton constructor, consider using a normal constructor to scope the state to specific widgtes, eg. with Provider.