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mvflow's Introduction

MVFlow

Simple Android MVI architecture using kotlin flows*

* The library is platform-neutral but was designed with Android in mind

CI status CI status Download

Check our website for all information about the library!

Objectives

We set off with the objective of creating a minimalistic library, simple yet with all the capabilities you need.

Minimalistic yet complete

MVFlow has a very small API surface. It strives to be the smallest conceivable MVI library that could exist. In just a few minutes you will know everything there is to know about the API!

Simple

The library introduces few - if any - new concepts outside MVI, Kotlin coroutines, and Kotlin flows.

If you are familiar with those concepts, you can start using the library without a problem; if you are new to some of these concepts, you will be able to apply those concepts outside this library too.

Coroutines and flows as powerful abstractions

We believe that coroutines and flows are extremely powerful concepts that can be applied to the MVI architecture. They enable us to build a very powerful API with a small and simple surface.

Here are some advantages that they bring:

  • Coroutines make asynchronous calls very simple to write and easy to reason about;

  • Flows are a great abstraction to represent user events (clicks) and updates from background work;

  • Coroutine scopes make handling the lifecycle of requests very simple

API

You can find a guide to this library on MVFlow's website.

If you would like to take a look behind the scenes, MVFlow.kt contains all the logic in this library. PRs and feedback welcome!

You can also browse the code of the sample Android app.

Inspiration

This library got a lot of inspiration from other libraries. We would like to thank:

And everyone who contributed towards those libraries (and their respective inspirations).

mvflow's People

Contributors

ablenesi avatar pedroql avatar

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mvflow's Issues

Handler State Become Stale for Actions That Produce Long Running Flows

There are a couple ways I can see to fix this, neither of which is backwards compatible.

  1. Pass StateFlow<State> as parameter instead of State in Handler
typealias Handler<State, Action, Mutation> = (StateFlow<State>, Action) -> Flow<Mutation>

//Flow<Action>.collectIntoHandler changes to
handler.invoke(state, action, LoggingEffectSender(logger))

//Inside handler functions the current state can be accessed using
{ state, action ->
  state.value
}
  1. Pass function () -> State as parameter instead of State in handler
typealias Handler<State, Action, Mutation> = (() -> State, Action) -> Flow<Mutation>

//Flow<Action>.collectIntoHandler changes to
handler.invoke({state.value}, action, LoggingEffectSender(logger))

//Inside handler functions the current state can be accessed using
{ state, action ->
   state()
}

Example: Notice that MyState(count=1) and MyState(count=2) are printed when it should print all the way up to count=6

data class MyState(val count: Int = 1)
  sealed class MyAction {
    object Start : MyAction()
  }

  sealed class MyMutation {
    data class IncrementCount(val newCount: Int) : MyMutation()
  }

  @Test
  fun testStaleState() {
    runBlocking {
      val handler: Handler<MyState, MyAction, MyMutation> = { state, action ->
        when (action) {
          MyAction.Start -> flow {
            emit(MyMutation.IncrementCount(state.count + 1))
            kotlinx.coroutines.delay(100)
            emit(MyMutation.IncrementCount(state.count + 1))
            kotlinx.coroutines.delay(100)
            emit(MyMutation.IncrementCount(state.count + 1))
            kotlinx.coroutines.delay(100)
            emit(MyMutation.IncrementCount(state.count + 1))
            kotlinx.coroutines.delay(100)
            emit(MyMutation.IncrementCount(state.count + 1))
          }
        }
      }
      val reducer: Reducer<MyState, MyMutation> = { state, mutation ->
        when(mutation){
          is MyMutation.IncrementCount -> state.copy(count =  mutation.newCount)
        }
      }
      MVFlow(MyState(), handler, reducer, this).takeView(this, object : MVFlow.View<MyState, MyAction>{
        override fun actions(): Flow<MyAction> {
          return flowOf(MyAction.Start)
        }

        override fun render(state: MyState) {
          println(state)
        }
      })
    }
  }

Android sample app wont even sync on latest Android Studio Iguana

Can't get the sample app to compile or even Gradle sync, opened the sample_app folder in Android Studio Iguana and no matter what jdk I select I get:

BUG! exception in phase 'semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 61

Ability to allow same Flow emission

We're implementing our click events (e.g: buttonA), but unable to (re)click the buttonA unless we're resetting the events/click another events

The buttonA is just a simple showing bottom dialog, we're providing an ID to its intent then fetch API and display the data retrieved from server

Is it possible to allow same flow emission for particular/specific events? or should we implement reset state instead manually?

Consider moving from SharedFlow to Channel

MVFlow uses a SharedFlow to handle the Effects, then launchWhenX {} in the View to collect the effects.

However this raises some good points about not using SharedFlow and instead use a Channel(Channel.BUFFERED). Because some Effects can be lost due to configuration changes. And even using launchWhen(Started/Resumed) {} is not immune to this, and he proposes a simple observer class to handle it.

How to stop an async task launched by the handler

I have a serch that each time that you type a character it launches a request. The problem is that if I don't cancel I could have this race condition:

  • Action Search "mv"
  • Action Search "mvf"
  • Mutation with items from "mvf"
  • Mutation with items from "mv"

At the end the user sees the results of "mv" instead of "mvf".

If I can cancel the collection of the current old flow I would fix it. Maybe there is other way to avoid this problem. I tried out this one: badoo/MVICore#68 (comment) but Flow doesn't have a takeUntil.

Best practices to send a throwable from Fragment/Activity?

MVFlow class

    sealed class Error : Action {
       object MaxChar : Error()
       object NPE : Error()
       object UPA : Error()
    }

In Activity/Fragment

private val actionsChannel = Channel<Action>()

// somewhere in the code
// e.g: 1
viewBinding.editText.doAfterTextChanged {
   if (it.length > 200) actionsChannel.offer(Action.Error.MaxChar)
}

// e.g: 2

try { 
    doSomething(null)
} catch (e: NullPointerException) {
    actionsChannel.offer(Action.Error.NPE)
}

fun doSomething(nonNull: String) {
 // do something
} 

// e.g: 3

private var lateinit abc: String

// we forgot to initialized,
// therefore will throw UninitializedPropertyAccessException: lateinit property `abc`
try { 
   doSomething(abc) 
} catch (e: UninitializedPropertyAccessException) {
   actionsChannel.offer(Action.Error.UPA)
}

Question

or is there any alternative to distinguish between throwing errors in our view (e.g: without an action), maybe using Effects #30?

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