ApiService.kt

package com.studio.mattiaferigutti.hilt_usage_sample

interface ApiService {

    suspend fun getText() : Reply
}

ApiServiceImpl.kt

package com.studio.mattiaferigutti.hilt_usage_sample

import okhttp3.*
import java.io.IOException
import javax.inject.Inject

class ApiServiceImpl @Inject constructor(private val request: Request) : ApiService {
    override suspend fun getText(): Reply {
        var result = ""
        val client = OkHttpClient()

        client.newCall(request).enqueue(object : Callback {
            override fun onFailure(call: Call, e: IOException) {
                e.printStackTrace()
                result = e.toString()
            }

            override fun onResponse(call: Call, response: Response) {
                result = response.body.toString()
            }
        })
        return Reply(result)
    }
}

ApplicationModule.kt

package com.studio.mattiaferigutti.hilt_usage_sample

import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.android.components.ActivityComponent
import dagger.hilt.android.internal.managers.ApplicationComponentManager
import dagger.hilt.components.SingletonComponent
import okhttp3.*
import java.io.IOException
import javax.inject.Singleton

@Module
@InstallIn(SingletonComponent::class)
class ApplicationModule {
  
    @Provides
    @Singleton
    fun provideRetrofit() : Request {
        return Request.Builder()
            .url("http://www.massimocarli.eu/bus/bus_stop.json")
            .build()
    }

    @Provides
    fun provideApiService(request: Request) : ApiService {
        return ApiServiceImpl(request)
    }
}

MainRepository.kt

package com.studio.mattiaferigutti.hilt_usage_sample

import javax.inject.Inject

class MainRepository @Inject constructor(val result: ApiService) {
    suspend fun getResult() : String {
        return result.getText().message
    }
}

SecondFragmentViewModel.kt

package com.studio.mattiaferigutti.hilt_usage_sample

import androidx.hilt.lifecycle.ViewModelInject
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.launch

class SecondFragmentViewModel @ViewModelInject constructor(
    private val mainRepository: MainRepository
)
: ViewModel() {

    private val _data = MutableLiveData<String>()
    val data : LiveData<String>
        get() = _data

    init {
        fetch()
    }

    private fun fetch() {
        viewModelScope.launch {
            _data.postValue(mainRepository.getResult())
        }
    }
}