Enjoy DI life with Koin - Aaron Chu
===
### Dagger2
Dagger2 has too many annotations and it's too complicated to use.

## Koin
### What is Koin?
A pragmatic lightweight dependency injection framework for Kotlin developers.
**Koin is a DSL, a lightweight container and a pramatic API.**

### Koin Setup(1/2)
Define module

val repoModule = module  {
    single { ... }
    factory { ... }
}

`single` -> Singleton

### Koin Setup(2/2)
`Start Koin`

startKoin {
    ...
}

### Koin Injection

// Lazy injection
private val repo: FeatureRepo by inject()

// Injects immediately
private val repo: FeatureRepo by get()

### Binding an Interface

private val repo: FeatureInterface by inject()

### Naming definitions

### Where are `inject()` and `get()` from?
`inject()` and `get()` are extension function of Kolin.

## MVP(Model-View-Presenter) with Koin

val presenterModule = module {
    // With MainActivity's lifecycle
    scope(named<MainActivity>()) {
        scoped<Presenter> {
            FeaturePresenter()
        }
    }
}

MainActivity {
    private val presenter: FeatureContract.Presenter by currentScope.inject {
        parametersOf(this)
    }
}

### Where is current scope from?

## MVVM(Model-View-ViewModel) with Koin
###
Get ViewModel in other FragmentActivity

private val viewModel: FeatureViewModel by viewModel()

Get ViewModel in other fragments

private val viewModel: FeatureViewModel by sharedViewModel()

## Inject anywhere

interface KoinComponent {
    fun getKoin(): Koin = GlobalContext.get().koin
}

class ApiClient : KoinComponent {
    private val apiClient: ApiClient by inject()
}

Example of ViewController
// TODO

### Inject view model declared in viewModel() anywhere?
No, because ViewModel is tied to Activity or Fragment

Solution: use the instance of `FragmentActivity` or `Fragment` to inject viewModel.

## Unit test
### Check Modules

class MyTest
    @Test
    fun `check modules`() {
        startKoin {
            modules(viewModelModule)
        }
    }.checkModules()

* unit test 結束後記得要做stopKoin

### Check Modules with Parameters

### Declare Mocks on the Fly

###### tags: `DevFest2019`