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(MVI) Model View Intent

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Devrath edited this page Feb 19, 2024 · 19 revisions

Improvement from MVI towards a better Architecture

  • To overcome the drawbacks of MVC controller overloading with the business logic. Modifications were done to segregate it to a better representation of architecture called Model-View-Presenter.
  • It is a relatively new but popular approach to android application architecture.

MVI specific concepts

  • Uni-directional data flow.
  • Immutable state.
  • User as a function.
  • Its way of simplifying the flow of information which leads to a comprehensive and systematic approach to architecture.

How the concept of MVI came into existence

  • Many of the advancements in recent times comes from the web-development world.
  • Some namely react, redux, flux, use event-driven and functional way of solving things.
  • They give a unique perspective on how to manage mutable state.
  • Such representation fits into mobile development applications.
  • MVI is closely associated with cycle.js from the web development world.

How MVI works

Most important part of the Architecture - User

  • Much of the code you write in web development is user focused instead of process intensive.
  • Architecture in android usually focus on the process instead of user. The code gives an interface to accept input and send input.
  • Place of the user in mvvm or mvp is not transparent. Usually, the user is the kind of view in these patterns.

In MVI user takes a central role in expressing their intents(intention).

Overview representation of MVI

  • Application starts up and the user starts interacting with it.
  • We call user interaction intents meaning users intents on something to occur based on how they interact with the application. They might type a text or click a button.
  • Our software does something interesting using the intents(intention) of the user and models the data and the output is sent back to the user.
  • Thus there are intents as input and results as output.

Detailed representation of MVI

  • We interpret the user intents as actions that have to be taken inside our application.
  • We perform this translation from intent to action to take data within our application.
  • This translation will take users to the repository part, which is network-based, local storage-based or both.
  • We use processors to perform actions on our data.
  • The processors produce a result.
  • At this point, the user intent is translated into a result.
  • Now we need to get the results back to the user.

Immutable State

  • Here is the idea of the state coming into the picture.
  • State is the current status of all the information shown to the user.
  • In the High level of Android application state includes loading state, empty state, or state of particular data.
  • As the events occur, the states are continuously updated based on the events that have occurred.
  • Instead of maintaining the states as mutable objects in our system, In MVI a new state is calculated for each new event that occurs.
  • NewState = PreviousState + Results
  • The process of combining the states with results is called MVI in Android.
  • The new state is passed along to the android app which renders the UI to the user
  • Due to this the state is never mutable, instead, it's recalculated and passed to the view for rendering.
  • one of the sources of bugs in software is mutable states. - > Now by using immutable state -> We can eliminate the source of many bugs in software using MVI.

MVI - Layers

View Layer

  • Displays the objects in the layout/composable.
  • It observes the model state using rxJava/Flow

Model

  • The model represents a state, The models in the MVI should be immutable to ensure unidirectional data flow between them and other layers in the architecture
  • The model is what the view observes. The model is observed by the view.
  • Model also holds the state of the view.

Intent

  • The model receives the intent from the user(view).
  • Intent in MVI means -> The intent to do something, It is not related to the Android component.
  • Ex: User actions.

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