Kotlin, reduce duplicated code - kotlin

Question

Every my API service interface class have create static method,
interface AuthApiService {
#FormUrlEncoded
#POST("api/auth/login")
fun postLogin(#Field("username") username: String, #Field("password") password: String):
io.reactivex.Observable<LoginApiResponse>
companion object Factory {
fun create(): AuthApiService {
val gson = GsonBuilder().setLenient().create()
val retrofit = Retrofit.Builder()
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl("http:192.168.24.188:8080")
.build()
return retrofit.create(AuthApiService::class.java)
}
}
}
interface BBBApiService {
companion object Factory {
fun create(): BBBApiService {
val gson = GsonBuilder().setLenient().create()
val retrofit = Retrofit.Builder()
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl("http:192.168.24.188:8080")
.build()
return retrofit.create(BBBApiService::class.java)
}
}
}
But, I want to define the create() method only once.
So I made the ApiFactory class,
interface ApiFactory {
companion object {
inline fun <reified T>createRetrofit(): T {
val gson = GsonBuilder().setLenient().create()
val retrofit = Retrofit.Builder()
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl("http://192.168.24.188:8080")
.build()
return retrofit.create(T::class.java)
}
}
}
interface AuthApiService {
#FormUrlEncoded
#POST("api/auth/login")
fun postLogin(#Field("username") username: String, #Field("password") password: String):
io.reactivex.Observable<LoginApiResponse>
companion object Factory {
fun create(): AuthApiService {
return ApiFactory.createRetrofit()
}
}
But, still, I need to define the create() method in AuthApiService.
Is there any a way implement the ApiFactory class to SubApi classes so that I don't have to define the create method in each child classes?

Answer 1

A simple solution is just to call the function of your ApiFactory directly:
val authApiService = ApiFactory.createRetrofit<AuthApiService>()
But if you want to be able to call AuthApiService.create(), then you can define a marker interface, say, ApiFactoryClient<T>, and mark an empty companion object with it.
interface ApiFactoryClient<T>
interface AuthApiService {
/* ... */
companion object : ApiFactoryClient<AuthApiService>
}
And then make an extension function that works with ApiFactoryClient<T>:
inline fun <reified T> ApiFactoryClient<T>.create(): T = ApiFactory.createRetrofit<T>()
And the usage would be:
val authApiService = AuthApiService.create()

Answer 2

You can modify your ApiFactory like this:
interface ApiFactory {
companion object {
inline fun <reified T>createRetrofit(klass: KClass<T>): T {
val gson = GsonBuilder().setLenient().create()
val retrofit = Retrofit.Builder()
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl("http://192.168.24.188:8080")
.build()
return retrofit.create(klass.java)
}
}
}
And then use it to create different service instances:
val authApiService = ApiFactory.createRetrofit(AuthApiService::class)