RecyclerView List items not displaying nor playing

Question

After coding a recyclerView MediaPlayer, the item lists refused to display after testing with emulator. I don't know what to do. Please your help is very important to me. All the codes below is what i tried that didn't work.

This is the MainActivity.java

 public class MainActivity extends AppCompatActivity { private ArrayList<Music> arrayList; private CustomMusicAdapter adapter; private RecyclerView recyclerView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); recyclerView = findViewById(R.id.recyclerViewList); arrayList = new ArrayList<>(); arrayList.add(new Music("001 Music", "Salutatio Actus paenitentialis", R.raw.adoremus_snctus)); arrayList.add(new Music("002 Music", "Collecta, Liturgia Verbi (Prima & Secunda)", R.raw.adoremusl_collecta_liturgia_verbi)); arrayList.add(new Music("003 Music", "Evangelium (Alleluia)", R.raw.evangelium_alleluia)); arrayList.add(new Music("004 Music", "Evangelium (Responses)", R.raw.evangelium_responses)); arrayList.add(new Music("005 Music", "Oratio universalis, Oratio super oblata", R.raw.oratio_universalis)); arrayList.add(new Music("006 Music", "Prex Eucharistica (two versions)", R.raw.prex_eucharistica)); arrayList.add(new Music("007 Music", "Praefatio (Sanctus)", R.raw.praefatio_sanctus)); arrayList.add(new Music("008 Music", "Acclamans (Mortem tuam)", R.raw.acclamans_mortem_tuam)); arrayList.add(new Music("009 Music", "Elevans, Ritus Communionis (Pater Noster)", R.raw.pater_noster)); arrayList.add(new Music("010 Music", "Ritus Pacis", R.raw.ritus_pacis)); arrayList.add(new Music("011 Music", "Oratio post communionem, Benedicto, Dimissio", R.raw.dimissio)); arrayList.add(new Music("012 Music", "Penitential Act, Kyrie-Christe-Kyrie", R.raw.aud_3)); arrayList.add(new Music("013 Music", "", R.raw.aud_3)); arrayList.add(new Music("014 Music", "", R.raw.aud_3)); arrayList.add(new Music("015 Music", "", R.raw.aud_3)); arrayList.add(new Music("016 Music", "", R.raw.aud_3)); adapter = new CustomMusicAdapter(this, R.layout.custom_music_row, arrayList); recyclerView.setAdapter(adapter); recyclerView.setHasFixedSize(false); } }

the cutom_music_row

 <?xml version="1.0" encoding="utf-8"?> <android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" xmlns:app="http://schemas.android.com/apk/res-auto" app:cardCornerRadius="7dp" app:cardElevation="4dp" app:cardUseCompatPadding="true"> <RelativeLayout android:padding="16dp" android:layout_width="match_parent" android:layout_height="wrap_content"> <ImageView android:id="@+id/ivMusic" android:layout_width="30dp" android:layout_height="40dp" android:layout_alignParentTop="true" android:src="@drawable/ic_lmusic" /> <TextView android:id="@+id/textName" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentTop="true" android:layout_marginStart="48dp" android:text="Song List" android:textColor="#16c15b" android:textSize="22sp" android:layout_marginLeft="30dp" /> <TextView android:id="@+id/txtSinger" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignStart="@+id/textName" android:layout_below="@+id/textName" android:text="Singer" android:textColor="#645506" android:textSize="18sp" android:layout_alignLeft="@+id/textName" /> <ImageView android:id="@+id/ivPlay" android:layout_width="30dp" android:layout_height="30dp" android:layout_toLeftOf="@id/ivStop" android:layout_marginRight="20dp" android:src="@drawable/ic_play"/> <ImageView android:id="@+id/ivStop" android:layout_width="30dp" android:layout_height="30dp" android:src="@drawable/stop_outline" android:layout_alignParentRight="true"/> </RelativeLayout> </android.support.v7.widget.CardView>

this is MyViewHolder

 class MyViewHolder extends RecyclerView.ViewHolder { ImageView mImageaplay, mImageStop; TextView mTitle, mDes; public MyViewHolder(@NonNull View itemView) { super(itemView); this.mImageaplay = itemView.findViewById(R.id.ivPlay); this.mImageStop = itemView.findViewById(R.id.ivStop); this.mTitle = itemView.findViewById(R.id.textName); this.mDes = itemView.findViewById(R.id.txtSinger); } }

This the CustomMusicAdapter

 public class CustomMusicAdapter extends RecyclerView.Adapter<MyViewHolder>{ private Context context; private int layout; private ArrayList<Music> myArraylist; private MediaPlayer mediaPlayer; private boolean flag=true; public CustomMusicAdapter(Context context, int custom_music_row, ArrayList<Music> myArraylist) { this.context = context; this.layout = layout; this.myArraylist = myArraylist; } @NonNull @Override public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) { final View itemView = LayoutInflater.from(parent.getContext()) .inflate(R.layout.custom_music_row, parent, false); return new MyViewHolder(itemView); } @SuppressLint("RecyclerView") @Override public void onBindViewHolder(@NonNull final MyViewHolder holder, final int position) { holder.setIsRecyclable(false); final Music music = myArraylist.get(position); holder.mTitle.setText(music.getName()); holder.mDes.setText(music.getSinger()); //Play Music Setup holder.mImageaplay.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { if (flag){ mediaPlayer=MediaPlayer.create(context,music.getSong()); flag=false; } if (mediaPlayer.isPlaying()){ mediaPlayer.pause(); mediaPlayer.start(); holder.mImageaplay.setImageResource(R.drawable.ic_play); }else { mediaPlayer.start(); holder. mImageaplay.setImageResource(R.drawable.ic_pause); } mediaPlayer.start(); } }); // stop player holder.mImageStop.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { if (!flag){ mediaPlayer.stop(); mediaPlayer.release(); flag=true; } holder.mImageaplay.setImageResource(R.drawable.ic_play); } }); } @Override public int getItemCount() { return myArraylist.size(); } public class ViewHolder { TextView textView_SongName, textView_artist; ImageView imageView_play, imageView_stop; private View convertview; LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE); public ViewHolder() { convertview = layoutInflater.inflate(layout, null); textView_SongName = convertview.findViewById(R.id.textName); textView_artist = convertview.findViewById(R.id.txtSinger); imageView_play = convertview.findViewById(R.id.ivPlay); imageView_stop = convertview.findViewById(R.id.ivStop); } } }

This is the model class Music.java

 public class Music { private String name; private String singer; private int song; public Music(String name, String singer, int song) { this.name = name; this.singer = singer; this.song = song; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSinger() { return singer; } public void setSinger(String singer) { this.singer = singer; } public int getSong() { return song; } public void setSong(int song) { this.song = song; } }

Answer 1

You pass myArrayList as an argument to CustomMusicAdapter , but do nothing with it in the constructor. Therefore myArrayList remains null in the adapter class.

public CustomMusicAdapter(Context context, int custom_music_row, ArrayList<Music> myArraylist) {
    this.context = context;
    this.layout = layout;
    this.myArraylist = myArraylist; // Add this line
}

As pointed out here you also need to set the LayoutManager in your MainActivity's onCreate:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ...

        adapter = new CustomMusicAdapter(this, R.layout.custom_music_row, arrayList);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this)); // Add this line
        recyclerView.setHasFixedSize(false);

    }

If it still does not work, you might need to append your MainActivity's xml file as well as the gradle file.

Do keep in mind though that this is a forum to ask specific questions and not a code review platform.

Some general tips:

1. the layout variable adds nothing to your code and can be removed. Same for the parameter custom_music_row

public CustomMusicAdapter(Context context, int custom_music_row, ArrayList<Music> myArraylist) {
    this.context = context;
    this.layout = layout; // remove this
    this.myArraylist = myArraylist;
}

2. As you already use a custom ViewHolder, you can remove this class entirely:

public class ViewHolder {
        TextView textView_SongName, textView_artist;
        ImageView imageView_play, imageView_stop;
        private View convertview;
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);

        public ViewHolder() {
            convertview = layoutInflater.inflate(layout, null);
            textView_SongName = convertview.findViewById(R.id.textName);
            textView_artist = convertview.findViewById(R.id.txtSinger);
            imageView_play = convertview.findViewById(R.id.ivPlay);
            imageView_stop = convertview.findViewById(R.id.ivStop);

        }
    }

Answer 2

检查这个

    recyclerView.setLayoutManager(new LinearLayoutManager(this));