一、简介

KOIN - a pragmatic lightweight dependency injection framework for Kotlin
https://insert-koin.io/

二、集成

根据情况引入对应的库

Android

// 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"

AndroidX

// Koin AndroidX Scope features
implementation "org.koin:koin-androidx-scope:$koin_version"
// Koin AndroidX ViewModel features
implementation "org.koin:koin-androidx-viewmodel:$koin_version"
// Koin AndroidX Experimental features
implementation "org.koin:koin-androidx-ext:$koin_version"

三、基本使用

1、创建被注入组件

interface HelloRepository {
    fun giveHello(): String
}

class HelloRepositoryImpl() : HelloRepository {
    override fun giveHello() = "Hello Koin"
}

class MySimplePresenter(val repo: HelloRepository) {
    fun sayHello() = "${repo.giveHello()} from $this"
}

2、创建Koin module

val appModule = module {
    // HelloRepository 单例
    single<HelloRepository> { HelloRepositoryImpl() }

    // Simple Presenter Factory
    factory { MySimplePresenter(get()) }
}

• module 类似dagger2中的 @Module
• single 单例模式
• factory 每次创建新的实例
• get()

3、Start Koin

class MyApplication : Application(){
    override fun onCreate() {
        super.onCreate()
        startKoin{
            androidLogger()
            androidContext(this@MyApplication)
            modules(appModule)
        }
    }
}

4、依赖注入

class MySimpleActivity : AppCompatActivity() {

    // Lazy injected 
    val firstPresenter: MySimplePresenter by inject()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //...
    }
}

// 更多方式
// non lazy
val firstPresenter: MySimplePresenter = get()

// lazy inject
private val homePresenter by inject<HomePresenter>()
// non lazy
private val homePresenter = get<HomePresenter>()

• by inject()

三、ViewModel使用

1、创建被注入组件

interface HelloRepository {
    fun giveHello(): String
}

class HelloRepositoryImpl() : HelloRepository {
    override fun giveHello() = "Hello Koin"
}

class MyViewModel(val repo : HelloRepository) : ViewModel() {
    fun sayHello() = "${repo.giveHello()} from $this"
}

2、创建module

val appModule = module {

    // single instance of HelloRepository
    single<HelloRepository> { HelloRepositoryImpl() }

    // MyViewModel ViewModel
    viewModel { MyViewModel(get()) }
}

3、Start Koin 同上面的Start Koin

4、依赖注入

class MyViewModelActivity : AppCompatActivity() {
    
    // Lazy Inject ViewModel
    val myViewModel: MyViewModel by viewModel()
    
    // non lazy
    //val myViewModel: MyViewModel = getViewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_simple)
        //...
    }
}

• viewModel：special DSL keyword to declare a ViewModel
• by viewModel() & getViewModel()：to inject ViewModel instance (from Activity & Fragment)
• by sharedViewModel() & getSharedViewModel()：to reuse ViewModel instance from hosting Activity (from Fragment)

四、Scope

val appModule = module {

    // single instance of HelloRepository
    single<HelloRepository> { HelloRepositoryImpl() }

    // Scoped MyScopePresenter instance
    scope(named<MyScopeActivity>()) {
        scoped { MyScopePresenter(get()) }
    }
}

class MyScopeActivity : AppCompatActivity() {

    // inject MyScopePresenter from current scope 
    val scopePresenter: MyScopePresenter by currentScope.inject()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_simple)

    }
}

The currentScope allows us to retrieve/create a Koin scope for given activity

五、其他

1、在module中使用 context

class MainApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin {
            // use AndroidLogger as Koin Logger - default Level.INFO
            androidLogger()
            // use the Android context given there
            androidContext(this@MainApplication)
    }
}

module {
    single { MyAndroidComponent(androidContext()) }
}

2、named使用

val myModule = module {
    single<Service>(named("default")) { ServiceImpl() }
    single<Service>(named("test")) { ServiceImpl() }
}

val service : Service by inject(name = named("default"))

val myModule = module {
    single<Service> { ServiceImpl1() }
    single<Service>(named("test")) { ServiceImpl2() }
}

Then:
val service : Service by inject() will trigger the ServiceImpl1 definition
val service : Service by inject(named("test")) will trigger the ServiceImpl2 definition

3、跨module使用

Koin does’t have any import concept. Koin definitions are lazy: a Koin definition is started with Koin container but is not instantiated. An instance is created only a request for its type has been done.

// ComponentB <- ComponentA
class ComponentA()
class ComponentB(val componentA : ComponentA)

val moduleA = module {
    // Singleton ComponentA
    single { ComponentA() }
}

val moduleB = module {
    // Singleton ComponentB with linked instance ComponentA
    single { ComponentB(get()) }
}

4、带参数注入

单参数

class Presenter(val view : View)

val myModule = module {
    single{ (view : View) -> Presenter(view) }
}

val presenter : Presenter by inject { parametersOf(view) }

多参数

class Presenter(val view : View, id : String)

val myModule = module {
    single{ (view : View, id : String) -> Presenter(view,id) }
}

// inject with view & id
    val presenter : Presenter by inject { parametersOf(this,id) }

5、 读取 property

创建koin.properties

/src/main/resoucres/koin.properties

// Key - value
server_url=http://service_url

startKoin {
    ...
    androidFileProperties()
    ...
}

val myModule = module {
    // use the "server_url" key to retrieve its value
    single { MyService(getProperty("server_url")) }
}

6、KoinComponent

Android中 inject() get()等方法在Activity和Fragment中已经默认存在；当你在其他类中需要使用时，你需要让其他类实现KoinComponent接口