Android Studio Firebase DataChange 异步和捆绑问题 (Java)

Question

当我从 Firebase 实时数据库调用时，onDataChange 方法遇到了某些问题。这些问题包括数据在 DataChange 方法之外消失。我尝试了此链接的解决方案， 如何返回 DataSnapshot 值作为方法？，它已经起作用了，但是，当我尝试将它传递给回调方法中的片段包时，它说值是 null 并且其中没有任何数据。对于我面临的这个问题有什么解决方法吗？非常感谢帮助，谢谢！

import edu.ntu.ssp4_rzdns_outhink.R;
import edu.ntu.ssp4_rzdns_outhink.modals.Attraction;

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

    private static final String TAG = "MostPopularRecyclerViewAdapter";
    private static final String SHARED_PREFS = "attractionsFile";
    private ArrayList<Attraction> pops;
    private Attraction attraction;
    private Context mContext;
    private FragmentManager fm;
    private Bundle bundle;
    SharedPreferences.Editor editor;
    SharedPreferences attractionFile;

    public MostPopularRecyclerViewAdapter(ArrayList<Attraction> pops, Context mContext, FragmentManager fm, Bundle bundle) {
        this.pops = pops;
        this.mContext = mContext;
        this.fm = fm;
        this.bundle = bundle;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        Log.d(TAG, "OnCreateViewHolder Called");
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_more_list, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Log.d(TAG, "onBindViewHolder Called");
        Glide.with(mContext).asBitmap().load(pops.get(position).photo_url).into(holder.attractionImage);
        holder.locationName.setText(pops.get(position).att_name);
        holder.locationRating.setText(pops.get(position).att_rating.toString());
        holder.locationAddress.setText(pops.get(position).att_address);
        holder.parentLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String attraction_id = pops.get(holder.getBindingAdapterPosition()).id;
                readData(new FirebaseCallback() {
                    @Override
                    public void onCallBack(Attraction attr) {
                        bundle.putString("attid", attr.id);
                        bundle.putString("name", attr.att_name);
                        bundle.putString("address", attr.att_address);
                        bundle.putString("desc", attr.att_desc);
                        bundle.putDouble("rating", attr.att_rating);
                        bundle.putString("url", attr.att_url);
                        bundle.putSerializable("ophrs", attr.att_op_hr);
                        bundle.putSerializable("adminrate",attr.att_admin_rate);
                        bundle.putString("photo_url", attr.photo_url);
                    }
                },attraction_id);
            }
        });
    }

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

    public static class ViewHolder extends RecyclerView.ViewHolder{

        ImageView attractionImage;
        TextView locationName;
        TextView locationAddress;
        TextView locationRating;
        RelativeLayout parentLayout;

        public ViewHolder(@NonNull View itemView){
            super(itemView);
            attractionImage = itemView.findViewById(R.id.viewmoreImage);
            locationName = itemView.findViewById(R.id.viewmoreName);
            locationAddress = itemView.findViewById(R.id.viewmoreLocation);
            locationRating = itemView.findViewById(R.id.viewmoreRating);
            parentLayout = itemView.findViewById(R.id.parent_layout_view_more);
        }
    }

    private void readData(FirebaseCallback firebaseCallback, String attrId){

        Query query = FirebaseDatabase.getInstance().getReference("attractions");
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (!snapshot.exists()) {
                    System.out.println("Attraction Does Not Exist");
                } else {
                    for (DataSnapshot attr : snapshot.getChildren()) {
                        if (attr.getKey().equals(attrId)) {
                            attraction = attr.getValue(Attraction.class);
                            attraction.setId(attr.getKey());
                        }
                    }
                    firebaseCallback.onCallBack(attraction);
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });
    }


    private interface FirebaseCallback{
        void onCallBack(Attraction attraction);
    }
}

Answer 1

根据你最后的评论：

当我尝试将这些变量放入包中时，它就会消失并变为 null。

请注意，这是预期的行为。您的代码中存在多个不一致之处。首先，这不是您在适配器类中处理单击事件的方式。将点击侦听器附加到显示的每个元素并不是一个可行的解决方案。您应该为此创建一个接口，如您在 repo。

现在，每次单击 RecyclerView 中的特定元素时，都会调用 readData() 方法。当您收到数据时，将该数据添加到捆绑包中。问题在于打开新片段的操作发生的速度比从数据库获取数据的速度快。这就是你变得 null 的原因。

为了解决这个问题，您可以仅在数据可用时导航到下一个片段，或者可以直接从第二个片段进行另一个调用。