Android recycler view not calling any function (Kotlin)

Question

I have a simple new application with a recycler view that should display "songs" but at the moment it displays non. Non of the functions on the adapter are being called, not even getItemCount.

What ive tried:

• ive set the background color of the recycler and I can see it appears on screen
• ive set the layout manager to linear, i tried once on xaml and once on code but non solved the issue
• ive set the adapter correctly and debugged that the construtor of the adapter is getting called and it is
• ive debugged to check weteher the list of items are empty or getItemCount returns 0 and it is not
• tried to call notifyDataSetChanged() after setting the adapter, no luck

I am not new to android, ive been developing on android xamarin, xamarin maui and now moved to android studio. I cant seem to find anything wrong with my code. Can anyone help? Thank you.

SongAdapter:

/**
 * Song adapter
 *
 * @property songs a given list of songs
 * @constructor Create empty Song adapter
 */
class SongAdapter(private val songs: MutableList<Song> = mutableListOf()) : RecyclerView.Adapter<SongAdapter.SongVH>() {

    /**
     * Song view holder
     *
     * @property songDisplayView the song display view being held
     * @constructor Create empty Song view holder
     */
    class SongVH(val songDisplayView: SongDisplayView) : ViewHolder(songDisplayView){
    }

    override fun getItemCount(): Int {
        return songs.count()
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SongVH {
        return SongVH(SongDisplayView(parent.context,null,songs[viewType]))
    }

    override fun onBindViewHolder(holder: SongVH, position: Int) {
        holder.songDisplayView.setSong(songs[position])
    }


    /**
     * Update songs to the given new songs
     *
     * @param newSongs given new songs
     */
    fun updateSongs(newSongs: Iterable<Song>){
        songs.clear()
        songs.addAll(newSongs)
        notifyItemRangeChanged(0,songs.size)
    }

    /**
     * Adds a new song to the song list
     *
     * @param newSong a given new song
     */
    fun addSong(newSong : Song){
        songs.add(newSong)
        notifyItemInserted(songs.size-1)
    }

    /**
     * Removes a song from the song list
     *
     * @param index a given index to remove from
     */
    fun removeSong(index: Int){
        songs.removeAt(index)
        notifyItemRemoved(index)
    }

    /**
     * Updates the song at the given index to a new song
     *
     * @param song the new song
     * @param index a given index
     */
    fun updateSong(song: Song, index: Int){
        songs[index] = song
        notifyItemChanged(index)
    }
}

SongDisplayView:

class SongDisplayView(context: Context,attributeSet: AttributeSet?,song: Song = Song()) : LinearLayout(context,attributeSet) {

    private val titleView: TextView = TextView(context)
    init {
        titleView.text = song.name
        titleView.textSize = 18f
        addView(titleView)
    }

    fun setSong(song: Song ) {
        titleView.text = song.name
    }
}

MainActivity:

class MainActivity : AppCompatActivity() {

    private lateinit var binding : ActivityMainBinding

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

        binding = ActivityMainBinding.inflate(layoutInflater)

        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)) { v, insets ->
            val systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars())
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
            insets
        }
        val songAdapter = SongAdapter(mutableListOf(Song("Song 1"),Song("Song 2"), Song("Song 3")))
        binding.songsRecycler.adapter = songAdapter
        songAdapter.notifyDataSetChanged()
    }
}

activity_main layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity" >
<TextView
    android:text="hello world"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>
    <androidx.recyclerview.widget.RecyclerView
        android:background="#fadada"
        android:id="@+id/songsRecycler"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

Answer 1

You're able to see the background color of the recycler because you initially set the layout using setContentView(R.layout.activity_main).

But you inflated the same activity_main layout again using viewBinding. Then you setup the recycler (binding.songsRecycler) from this newly inflated layout.

The newly inflated layout remains invisible until you set it as the content view using setContentView(binding.root). That's why recycler items aren't displayed.

Solution

Just set binding.root in setContentView.

class MainActivity : AppCompatActivity() {

    private val binding by lazy { ActivityMainBinding.inflate(layoutInflater) }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContentView(binding.root)
        // other codes ...
    }
}