build.gradle

    // ...
    
    implementation "android.arch.lifecycle:viewmodel:$versions.architectureComponents"
    implementation "android.arch.lifecycle:extensions:$versions.architectureComponents"

    // ...

MusicContentViewModel.kt

import android.arch.lifecycle.ViewModel
import com.mataku.scrobscrob.app.model.entity.Artist
import com.mataku.scrobscrob.app.model.entity.Album

class MusicContentViewModel : ViewModel() {
    var artists = mutableListOf<Artist>()
    var albums = mutableListOf<Album>()
}

TopAlbumsContentFragment.kt

package com.mataku.scrobscrob.app.ui.fragment.artist

import android.arch.lifecycle.ViewModelProviders
import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.mataku.scrobscrob.R
import com.mataku.scrobscrob.app.model.MusicContentViewModel
import com.mataku.scrobscrob.app.model.entity.Album
import com.mataku.scrobscrob.app.presenter.TopAlbumsPresenter
import com.mataku.scrobscrob.databinding.FragmentTopArtistsBinding

class TopAlbumsContentFragment : Fragment() {

    private lateinit var binding: FragmentTopAlbumsBinding
    private val presenter = TopAlbumsPresenter()

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_top_albums, null, false)
        view?.let {
            binding = DataBindingUtil.bind(it)!!
            setUp()
        }
        return view
    }
  
    override fun show(albums: List<Album>) {
        viewmodel.albums.addAll(albums)
        // データ渡して UI に反映
    }

    private fun setUp() {
        this.activity?.let {
            val viewmodel = ViewModelProviders.of(it).get(MusicContentViewModel::class.java)
            if (viewmodel.albums.isNotEmpty()) {
                // データがあれば通信せずにそれを使って表示
            } else {
                presenter.getTopAlbums()
            }
        }
    }
}

TopArtistContentFragment.kt

package com.mataku.scrobscrob.app.ui.fragment.artist

import android.arch.lifecycle.ViewModelProviders
import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.mataku.scrobscrob.R
import com.mataku.scrobscrob.app.model.MusicContentViewModel
import com.mataku.scrobscrob.app.model.entity.Artist
import com.mataku.scrobscrob.app.presenter.TopArtistsPresenter
import com.mataku.scrobscrob.databinding.FragmentTopArtistsBinding

class TopArtistsContentFragment : Fragment() {

    private lateinit var binding: FragmentTopArtistsBinding
    private val presenter = TopArtistsPresenter()

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_top_artists, null, false)
        view?.let {
            binding = DataBindingUtil.bind(it)
            setUp()
        }
        return view
    }
  
    override fun show(artists: List<Artist>) {
        viewmodel.artists.addAll(artists)
        // データ渡して UI に反映
    }

    private fun setUp() {
        this.activity?.let {
            val viewmodel = ViewModelProviders.of(it).get(MusicContentViewModel::class.java)
            if (viewmodel.artists.isNotEmpty()) {
                // データがあれば通信せずにそれを使って表示
            } else {
                presenter.getTopArtists()
            }
        }
    }
}