Mini

⚠️ DOCS HAVE TO BE UPDATED FOR VERSION 3.x.y

Mini is a minimal Flux architecture written in Kotlin that also adds a mix of useful features to build UIs fast.

Purpose

You should use this library if you aim to develop a reactive application with good performance (no reflection using code-gen). Feature development using Mini is fast compared to traditional architectures (like CLEAN or MVP), low boilerplate and state based models make feature integration and bugfixing easy as well as removing several families of problems like concurrency or view consistency across screens.

How to Use

Dispatcher

The Dispatcher is the hub that manages all data flow in a Flux application. It is basically a holder of store callbacks: each store registers itself and provides a callback for an action.

One important thing is that the dispatching is always performed in the same thread to avoid possible side-effects.

We can dispatch actions in the following ways:

// Dispatch an action on the main thread synchronously
dispatcher.dispatch(action = LoginAction(username = "user", password = "123"))

// Dispatch an action on the given scope
dispatcher.dispatchOn(action = LoginAction(username = "user", password = "123"), scope = coroutineScope)

Store

The Stores are holders for application state and state mutation logic. In order to do so they expose pure reducer functions that are later invoked by the dispatcher. A Store is a type of a StateContainer, which is exactly that: a container of states.

The state is a plain object (usually a data class) that holds all information needed to display the view. States should always be immutable. State classes should avoid using framework elements (View, Camera, Cursor...) in order to facilitate testing.

Stores subscribe to actions to change the application state after a dispatch. Mini generates the code that links dispatcher actions and stores using the @Reducer annotation over a non-private function that receives an Action as parameter.

data class SessionState(val loginTask: Task = taskIdle(), val loggedUser: User? = null)

class SessionStore @Inject constructor(val controller: SessionController) : Store<SessionState>() {
    @Reducer
    fun login(action: LoginAction): SessionState {
        controller.login(action.username, action.password)
        return state.copy(loginTask = taskRunning(), loggedUser = null)
    }

    @Reducer
    fun loginComplete(action: LoginCompleteAction): SessionState {
        return state.copy(loginTask = action.loginTask, loggedUser = action.user)
    }
}

Actions

An Action is a simple class that usually represents a use case. It can also contain a payload that includes data to perform said action. When an action is triggered, it will be delivered via dispatcher to the stores that are going to do something with the action to change their state.

For example, we may want to log in to a service. We would create an action like this one:

@Action
data class LoginAction(val username: String, val password: String)

When we receive the response from the server, we'll dispatch another action with the result:

@Action
data class LoginCompleteAction(val loginTask: Task, val user: User?)

Actions will usually be triggered from Views or Controllers.

View changes

Each StateContainer exposes a Kotlin Flow that emits changes produced on the state, allowing the view to listen reactive those changes. Being able to update the UI according to the new StateContainer state.

mainStore.flow()
         .onEach { state ->
              // Do whatever you want
         }.launchInLifecycleScope()

Tasks

A Task is a basic object to represent an ongoing process. They should be used in the state of our StateContainer (a Store, for example) to represent ongoing processes that must be represented in the UI.

You can also use TypedTask to save metadata related the current task.

IMPORTANT: Do not use TypedTask to hold values that must survive multiple task executions. Save them as a variable in the state instead.

Example

Given the example Stores and Actions explained before, the workflow would be:

• View dispatches LoginAction.
• Store changes his LoginTask status to running and call though his SessionController which will do all the async work to log in the given user.
• View shows an Spinner when LoginTask is in running state.
• The async call ends and LoginCompleteAction is dispatched on UI, sending a null User and an error state Task if the async work failed or a success Task and an User.
• The Store changes his state to the given values from LoginCompleteAction.
• The View redirect to the HomeActivity if the task was success or shows an error if not.

You can execute another sample in the app package. It contains two different samples executing two types of StateContainers:

• StoreSampleActivity class uses a Store as a StateContainer.
• ViewModelSampleActivity class uses a ViewModel as a StateContainer.

Kotlin Flow Utils

Mini includes some utility extensions over Kotlin Flow to make easier listen state changes over the StateContainers.

• select: Will emit only not null values over the given map clause.
• selectNotNull: Like select but avoiding null values.
• onEachChange: Emits a value when the values goes from one value to another.
• onEachDisable: Emits when the value goes from true to false.
• onEachEnable: Emits when the value goes from false to true.

Navigation

To avoid loops over when working with navigation based on a process result. You will need to make use of onNextTerminalState after dispatch and Action that starts a process which result could navigate to a different screen. For example:

  fun login(username: String, password: String) {
        dispatcher.dispatch(LoginAction(username, password))
        sessionStore.flowable()
                .onNextTerminalState(taskMapFn = { it.loginTask },
                        successFn = { navigateToLogin() },
                        failureFn = { showError(it) })
    }

If we continually listen the changes of a Task and we navigate to a specific screen when the Task becomes successful. The state will stay on SUCCESS and if we navigate back to the last screen we will be redirected again.

Logging

Mini includes a custom LoggerMiddleware to log any change in your StateContainer states produced from an Action. This will allow you to keep track of your actions, changes and side-effects more easily. To add the LoggerMiddleware to your application you just need to add a single instance of it to your Dispatcher after initialize it in your Application class or dependency injection code.

val loggerMiddleware = CustomLoggerMiddleware(stores().values)
dispatcher.addMiddleware(loggerMiddleware)

Testing with Mini

Mini includes an extra library called mini-android-testing with a few methods and Expresso TestRules to simplify your UI tests over this architecture.

• TestDispatcherRule : This rule will intercept any action that arrives to the Dispatcher, avoiding any call to the Store and their controllers. If we include this rule we will need to change the states manually in our tests.
• CleanStateRule : It just reset the state of your stores before and after each test.

Example of test checking that an action is correctly dispatched:

@get:Rule
val testDispatcher = testDispatcherRule()

@Test
fun login_button_dispatch_login_action() {
    onView(withId(R.id.username_edit_text)).perform(typeText("someUsername"))
    onView(withId(R.id.password_edit_text)).perform(typeText("somePassword"))
    onView(withId(R.id.login_button)).perform(click())
    
    assertThat(testDispatcher.actions, contains(LoginAction(someUsername, somePassword)))
}

Example of test checking that a view correctly changes with an specify state:

@get:Rule
val cleanState = cleanStateRule()

@Test
fun login_redirects_to_home_with_success_task() {
     //Set login state to success
     onUiSync {
         val loggedUser = User(email = MockModels.anyEmail, uid = MockModels.anyId, username = MockModels.anyUsername, photoUrl = MockModels.anyPhoto)
         val state = SessionState().copy(loginRequestState = requestSuccess(), verified = false, loggedIn = true, loggedUser = loggedUser)
         sessionStore.setTestState(state)
     }
     //Redirect to Email verification activity
     intended(hasComponent(HomeActivity::class.java.name))
}

Setting Up

Import the library

Add the following dependencies to your main build.gradle:

allprojects {
    repositories {
        maven { url "https://jitpack.io" }
    }
}

Add the following dependencies to your app's build.gradle:

dependencies {
    def mini_version = "3.0.0"
    // Minimum working dependencies
    implementation "com.github.hyperdevs-team.mini-kotlin:mini-android:$mini_version"
    kapt "com.github.hyperdevs-team.mini-kotlin:mini-processor:$mini_version"

    // Kodein helper libraries
    implementation "com.github.hyperdevs-team.mini-kotlin:mini-kodein:$mini_version"
    implementation "com.github.hyperdevs-team.mini-kotlin:mini-kodein-android:$mini_version"
    // Kodein helper library for view models scoped to the Navigation component's graph in Jetpack Compose
    implementation "com.github.hyperdevs-team.mini-kotlin:mini-kodein-android-compose:$mini_version"

    // Testing helper libraries
    androidTestImplementation "com.github.hyperdevs-team.mini-kotlin:mini-testing:$mini_version"
}

Recommended settings

JDK8 requirements

Ensure that your project has compatibility with Java 8:

android {
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }

    kotlinOptions {
        jvmTarget = "1.8"
    }
}

Improve compilation speed

In order to speed up the compilation process, it is recommended to add the following settings in your gradle.properties:

## Improves kapt speed with parallel annotation processing tasks, may impact in memory usage
kapt.use.worker.api=true
## Enables Gradle build cache
org.gradle.caching=true

[Android] Setting up your App file

You'll need to add the following snippet to your Application's onCreate method. If you don't have it, then create it and reference it in your AndroidManifest.xml file:

val stores = listOf<Store<*>>() // Here you'll set-up you store list, you can retrieve it using your preferred DI framework
val dispatcher = MiniGen.newDispatcher() // Create a new dispatcher

// Initialize Mini
storeSubscriptions = MiniGen.subscribe(dispatcher, stores)
stores.forEach { store ->
    store.initialize()
}

// Optional: add logging middleware to log action events
dispatcher.addMiddleware(LoggerMiddleware(stores)) { tag, msg ->
    Log.d(tag, msg)
}

[Android] Kodein Android utils

mini-kodein-android has some utility methods in order to inject an Android's ViewModel in a DIAware Activity or Fragment. In order to use them, bind the Android's ViewModelProvider.Factory instance with Kodein:

// Use any tag to differ between the injected `Context` or `Application` if you are binding also `Context` with Kodein
bind<Application>("appTag") with singleton { app }
bind<ViewModelProvider.Factory>() with singleton { DIViewModelFactory(di.direct) }

To inject a ViewModel without parameters, bind it as follows:

bindViewModel { MainViewModel(instance("appTag") }

And in your DIAware Activity or Fragment:

private val mainViewModel: MainViewModel by viewModel()

mini-kodein-android-compose has some utility methods in order to inject an Android's ViewModel in the scope of a Navigation component graph. This is useful as in Jetpack Compose it is common to have only one or few Activities and no Fragments so, in order to scope the lifecycle of the ViewModel not for all the life of the Activity, we can scope it to any route existing in the NavBackStackEntry. In order to use it, do the same as above, but instead of injecting the ViewModel scoped to a route of the Navigation, the NavHost composable must be inside an DIAware Activity, and then do as follows:

composable(route = "home") { navBackStackEntry ->
    val homeViewModel: HomeViewModel by navBackStackEntry.viewModel(contextDI())
    HomeScreen(homeViewModel, ...)
}

In case you want to pass an argument to a ViewModel, you need to bind the factory of that kind of Android's ViewModel. You can do this in both mini-kodein-android, and mini-kodein-android-compose. For example, given a ViewModel that you want to pass a String param, it would be:

bindViewModelFactory<HomeViewModelWithParameter, ViewModelProvider.Factory> { param ->
    TypedViewModelFactory(HomeViewModelWithParameter::class, instance("appTag"), param as String)
}

And to retrieve it with the given param in its constructor:

val param = "Hello World!"
val homeViewModelWithParameter: HomeViewModelWithParameter by navBackStackEntry.viewModel(contextDI(), param)

[Android] Proguard/R8

Each of the libraries contain a sensible proguard file that your project can consume in order to run you app on Proguard or R8. No additional steps have to be done in order to use them apart from enabling minify in your project.

Acknowledgements

The work in this repository up to April 30th, 2021 was done by bq. Thanks for all the work!!

License

This project is licensed under the Apache Software License, Version 2.0.

   Copyright 2021 HyperDevs
   
   Copyright 2019 BQ

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.