This is a simple Android application that uses MVVM with

• Kotlin Koin for dependancy injection
• Retrofit for Network calls
• RxKotlin for thread management

Here are the steps taken to build an application using KOIN

Step 1

In build.gradle app must have these

// Koin for Android
    implementation "org.koin:koin-android:$koin_version"
// Koin Android Scope features
    implementation "org.koin:koin-android-scope:$koin_version"
// Koin Android ViewModel features
    implementation "org.koin:koin-android-viewmodel:$koin_version"
// Koin Android Experimental features
    implementation "org.koin:koin-android-ext:$koin_version"

    implementation "io.reactivex.rxjava2:rxjava:$rxjava_version"
    implementation "io.reactivex.rxjava2:rxkotlin:$rxkotlin_version"
    implementation "io.reactivex.rxjava2:rxandroid:$rxandroid_version"
    
    implementation "com.squareup.retrofit2:retrofit:$retrofit_version"
    implementation "com.squareup.retrofit2:converter-gson:$retrofit_version"
    implementation "com.squareup.retrofit2:adapter-rxjava2:$retrofit_version"
    implementation "com.squareup.retrofit2:converter-scalars:$retrofit_version"
    

Then make sure to have an Application class and add it into your manifest like KoinApplication.kt

Step 2

For every module/viewModels/Factory, just add those in their respective module variables in KoinApplication.kt, if there are new viewModels say UserViewModel

val viewModelModules = module{
            viewModel { UserViewModel(get(), get()) }
        }

The get() parameters are for modules already injected and needed for the viewModel class, like the LoginViewModel.kt has 2 params which are already injected in the

val networkModules = module {
            single{ AppModule()}
            single { AppModule().provideGson() }
            single { AppModule().provideOkHttpClientCredential(get()) }
            single{ AppModule().provideGeneralService(get(),get())}
            single{ AppModule().provideSchedulerProvider()}
        }

Step 3

Once the viewModel modules has been created, you can use them freely by injecting them with the by viewModel() keyword inside your activity. We call these lazy declaration.

val viewModel: LoginViewModel by viewModel()

Notes

In Koin there are 3 types of modules,

• single{} for singletons or instances. Invoke them with by inject()
• viewModel{} for viewModels. Invoke them with by viewModel()
• factory{} if you need new instance everytime. Invoke them with by get()

Reference taken from

• Understanding Dependency Injection with Koin - MVVM Clean Architecture for Android
• Dependency Injection with Kotlin for Android newbies! (Koin,Retrofit and Coroutines)
• Getting started with Android Architecture & ViewModel
• Android Dependency Injection with Koin