MVIKotlin

Overview

What is MVI

MVI stands for Model-View-Intent. It is an architectural pattern that utilizes unidirectional data flow. The data circulates between Model and View only in one direction - from Model to View and from View to Model.

What is MVIKotlin

MVIKotlin is a Kotlin Multiplatform framework that provides a way of (not only) writing shared code using MVI pattern. It also includes powerful debug tools like logging and time travel.

Responsibility

MVIKotlin does not bring or enforce any particular architecture. Its responsibility can be described as follows:

To provide a single source of truth for State (the scope is not defined, it can be a whole app, a screen, a feature, or a part of a feature);
To provide an abstraction for UI with efficient updates (however this is not obligatory, you can use whatever you want);
To provide lifecycle-aware connections (binding) between inputs and outputs (again this is not obligatory in any way).

Everything else is out of scope of the library, there are no definitions for “screens”, “features”, “modules”, etc. Also, no particular reactive framework is enforced/exposed. This gives a lot of flexibility:

MVIKotlin can be introduced incrementally (e.g. you can start using it in a small feature and then expand gradually);
You can use/experiment with different architectures, approaches and/or libraries for navigation, UI, modularization, etc;
Use whatever reactive framework you like or don’t use it at all.

You can find one of the architecture options in the samples. Again, this is just an example of one possible solution.

Core components

There are two core components in MVIKotlin:

Store - represents Model from MVI, this is the place for business logic
MviView - represents View from MVI, the UI part, optional

How the data flows

Please take a look at the following diagram:

The Store produces a stream of States which is transformed to a stream of View Models by a Mapper function (f). The View renders View Models and produces a stream of View Events which is transformed to a stream of Intents by another Mapper function (f). This makes the Store and the View independent from each other. You can also combine multiple States (multiple Stores) into a single View Model (single View), or multiple View Events (multiple Views) into a single Intent (single Store). But if you have only one Store and only one View and you need simplicity then your View can directly render States and produce Intents.

The View is subscribed to the stream of View Models and the Store is subscribed to the stream of Intents by a Binder. The Binder accepts start and stop signals and manages the subscriptions. The Binder is optional, you can subscribe components as you like.

The Store also produces a stream of Labels - one time events. They can be transformed to Intents and redirected to another Stores. Or you can use them for routing or to display errors or for any other actions that are not so important to be part of the State.

The data flows between core components only on Main thread.

Reactivity

MVI loves reactivity, it’s all about data streams and transformations. MVIKotlin is a reactive framework. But the main functionality of the framework does not depend on any such library. A tiny abstraction over Rx is used instead. Extensions for Reaktive and for Coroutines libraries are provided as separate modules.

Overview

Store

View

Binding and Lifecycle

State preservation

Logging

Time travel