RecyclerView Adapter 不会膨胀正确的布局

Question

当 arraylist PinnedSongs为空时，我试图让我的应用程序显示特定的布局。

我创建了不同的 viewholders 并试图根据PinnedSongs.size来膨胀它们。 意思是，如果它是 0，那么onCreateViewHolder应该膨胀一个特殊的布局。 如果不同，则再充气一个。

public class RecyclerAdapterHome extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    public class Viewholder extends RecyclerView.ViewHolder implements View.OnClickListener{

        CardView home_cardView;
        TextView home_textView;
        TextView home_textView_2;
        Button home_button;
        Button home_button_2;
        RelativeLayout parentlayout;
        OnNoteListener_2 onNoteListener2;
        public Viewholder(@NonNull View itemView, OnNoteListener_2 onNoteListener_2) {
            super(itemView);
            home_cardView = itemView.findViewById(R.id.cardview_2);
            home_textView = itemView.findViewById(R.id.cardview_2_textview);
            home_textView_2 = itemView.findViewById(R.id.cardview_2_textview_sub);
            home_button = itemView.findViewById(R.id.play_button);
            home_button_2 = itemView.findViewById(R.id.push_button);
            parentlayout = itemView.findViewById(R.id.home_parentlayout);
            home_button.setOnClickListener(this);
            this.onNoteListener2 = onNoteListener_2;
        }

        @Override
        public void onClick(View v) {
            onNoteListener2.onClick(getAdapterPosition());
        }
    }
    public class Viewholder_2 extends RecyclerView.ViewHolder {
        TextView textView_3;
        ImageView imageView;
        RelativeLayout parentlayout;
        public Viewholder_2(@NonNull View itemView) {
            super(itemView);
            textView_3 = itemView.findViewById(R.id.text_warning);
            imageView = itemView.findViewById(R.id.icon);
            parentlayout = itemView.findViewById(R.id.home_parentlayout);
        }
    }

    public RecyclerAdapterHome(OnNoteListener_2 mOnNoteListener2, ArrayList<String> pinnedSongs, ArrayList<String> pinnedSongsArtists, Context mContext) {
        this.mOnNoteListener2 = mOnNoteListener2;
        this.PinnedSongs = pinnedSongs;
        this.PinnedSongsArtists = pinnedSongsArtists;
        this.mContext = mContext;
    }

    private ArrayList<String> PinnedSongs = new ArrayList<>();
    private ArrayList<String> PinnedSongsArtists = new ArrayList<>();
    private Context mContext;
    private OnNoteListener_2 mOnNoteListener2;

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = null;
        if (PinnedSongs.size()==0){
            v = LayoutInflater.from(parent.getContext()).inflate(R.layout.nothing, parent, false);
            return new Viewholder_2(v);
        }else{
            v = LayoutInflater.from(parent.getContext()).inflate(R.layout.homeviewholder,
                    parent, false);
            return new Viewholder(v,mOnNoteListener2 );
        }
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
       if (PinnedSongs.size()==0){
           Viewholder_2 viewholder_2 = (Viewholder_2) holder;
        }else{
           Viewholder viewholder = (Viewholder) holder;
           viewholder.home_textView.setText(PinnedSongs.get(position));
           viewholder.home_textView_2.setText(PinnedSongsArtists.get(position));
       }
    }

    @Override
    public int getItemCount() {
        return PinnedSongs.size();
    }

    public interface OnNoteListener_2 {
        void onClick(int position);
    }
}

到目前为止，当 PinnedSongs 列表为零时，recyclerview 没有显示任何内容。 但是当它高于零时它会显示一些东西。 关于如何修复它的任何想法？

（如果与此有关，我正在使用 androidx 库）。

Answer 1

它不起作用，因为getItemCount方法返回0并且RecyclerView从不尝试实例化视图。

这意味着当 size=0 时不会调用onBindViewHolder 。

你有不同的选择来做到这一点。 其中之一是：

    @Override
    public int getItemCount() {
        return PinnedSongs.size() > 0 ? PinnedSongs.size() : 1;
    }

    @Override
    public int getItemViewType(int position) {
        if (PinnedSongs.size() == 0) {
            return EMPTY_VIEW;
        }
        return super.getItemViewType(position);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v;

        if (viewType == EMPTY_VIEW) {
            v = LayoutInflater.from(parent.getContext()).inflate(R.layout.nothing, parent, false);
            EmptyViewHolder emptyViewHolder = new EmptyViewHolder(v);
            return emptyViewHolder;
        }
        //normal case
        v = LayoutInflater.from(parent.getContext()).inflate(R.layout.homeviewholder, parent, false);
        ViewHolder viewholder = new ViewHolder(v);
        return viewholder;
    }

    public class EmptyViewHolder extends RecyclerView.ViewHolder {
        public EmptyViewHolder(View itemView) {
            super(itemView);
        }
    }

    private static final int EMPTY_VIEW = 1000;