java - RecyclerView 列表项目不显示也不播放

Question

编写 recyclerView MediaPlayer 后，在使用模拟器进行测试后，项目列表拒绝显示。我不知道该怎么办。请您的帮助对我来说非常重要。下面的所有代码都是我尝试过但不起作用的。

这是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);

    }
}

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>

这是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);
    }

}

这是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);

        }
    }
}

这是模型类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

您将 myArrayList 作为参数传递给 CustomMusicAdapter，但在构造函数中不对其执行任何操作。因此，myArrayList 在适配器类中保留 null。

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

正如所指出的here您还需要在 MainActivity 的 onCreate 中设置 LayoutManager:

@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);

    }

如果仍然不起作用，您可能需要附加 MainActivity 的 xml 文件以及 gradle 文件。

请记住，这是一个提出特定问题的论坛，而不是代码审查平台。

一些一般提示:

1. layout 变量不会向您的代码添加任何内容，并且可以将其删除。与参数 custom_music_row
相同

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

由于您已经使用了自定义 ViewHolder，因此您可以完全删除此类:

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);

        }
    }