android - RecyclerView不会为空

我的应用程序有一个带有项列表的主活动（比如说项A和项B），每个项都将启动相同的活动（UserGalleryActivity），但是Activity内的recyclerView应该仅显示与该项相关的项（将其称为A）在MainActivity中选择。

我的问题是，如果我首先选择（例如）项目A，它会正常工作，并且UserGalleryActivity中的RecyclerView仅显示A的项目，但是，当我返回MainActivity并选择B时，UserGalleryActivity向我显示A的项目以及B的项目。

如何解决此问题？任何想法？
先感谢您

UserGalleryActivity的代码：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_gallery);

    //L'activity riceve tramite intent dal main l'oggetto User
    Intent intent = getIntent();
    int user = intent.getIntExtra("user", -1);
    System.out.println("UserIndex: " + user);
    System.out.println(UsersSingleton.getInstance().getArray().get(user).getPhotos().size());
    if(user >= 0 && user<=UsersSingleton.getInstance().getArray().size()){
        String username = UsersSingleton.getInstance().getArray().get(user).getUsername();
        username = username.substring(0, 1).toUpperCase() + username.substring(1);
        UserGalleryActivity.this.setTitle(username);
        System.out.println("UserIndex: " + user);
        //System.out.println(UsersSingleton.getInstance().getArray().get(user).getPhotos().get(0).toString());
        setRecycleView(user);

    }

}


//Al termine della creazione dell'arraylist di users viene invocata setReView con parameto l'arraylist creato
private void setRecycleView(int userIndex){
    RecyclerView recyclerView = findViewById(R.id.photosList);
    recyclerView.setHasFixedSize(true);
    RecyclerView.LayoutManager layoutManager = new GridLayoutManager(this,2);
    recyclerView.setLayoutManager(layoutManager);
    MyAdapterPhotos adapter = new MyAdapterPhotos(this, userIndex);
    recyclerView.setAdapter(adapter);

MyAdapterPhotos的代码：

private int usersIndex;
private Context context;
JSONHelper jsonHelper;
URLHelper urlHelper;
ArrayList<Photo> photosList;
//Bitmap bitmap;


public MyAdapterPhotos(Context context, int usersList) {
    this.context = context;
    this.usersIndex = usersList;
    jsonHelper = new JSONHelper();
    urlHelper = new URLHelper();
    photosList = new ArrayList<>();

}

@NonNull
@Override

public MyAdapterPhotos.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.cell_layout_gallery,
            viewGroup, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {
    if (UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().get(position) != null){
        holder.title.setText(UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().get(position).getCity());
        holder.img.setScaleType(ImageView.ScaleType.CENTER_CROP);//prima era centercrop
        String username = UsersSingleton.getInstance().getArray().get(usersIndex).getUsername();
        username = username.substring(0, 1).toUpperCase() + username.substring(1);
        holder.author.setText(username);
        System.out.println("Numero di Foto: " + UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().size());
        System.out.println("Posizione: " + position);
        System.out.println(UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().get(position).toString());
        setImage(UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().get(position).getSmall(), holder.img);
    }


}

@Override
public int getItemCount() {
    return UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().size();
}

public class ViewHolder extends RecyclerView.ViewHolder{
    private TextView title;
    private ImageView img;
    private TextView author;

    public ViewHolder(View view){
        super(view);
        title = view.findViewById(R.id.title_g);
        img = view.findViewById(R.id.img_g);
        author = view.findViewById(R.id.author_g);


        // on image item click
        img.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                // get position
                int pos = getAdapterPosition();

                // check if item still exists
                if(pos != RecyclerView.NO_POSITION){
                    int clickedDataItem = pos;

                    /* for future animation
                    if (img.getDrawable() != null) {
                        bitmap = ((BitmapDrawable) img.getDrawable()).getBitmap();
                    } */

                    //se l'array di photo dell'utente è ancora vuoto, scaricale. altrimenti usa quelle che hai gia
                    Intent photosIntent = new Intent(context, PhotoDetailActivity.class);
                    photosIntent.putExtra("user", usersIndex);
                    photosIntent.putExtra("photo", clickedDataItem);
                    context.startActivity(photosIntent);

                    /*  for future animations
                    ActivityTransitionLauncher.with((AppCompatActivity) context)
                            .from(img)
                            .image(bitmap)
                            .launch(photosIntent);*/

                    //se l'array di photo dell'utente è ancora vuoto, scaricale. altrimenti usa quelle che hai gia


                }
            }
        });

        // on title item click
        view.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                // get position
                int pos = getAdapterPosition();

                // check if item still exists
                if(pos != RecyclerView.NO_POSITION){
                    //Photo clickedDataItem = UsersSingleton.getInstance().getArray().get(usersIndex).getPhotos().get(pos);
                    int clickedDataItem = pos;

                    //se l'array di photo dell'utente è ancora vuoto, scaricale. altrimenti usa quelle che hai gia
                    Intent photosIntent = new Intent(context, PhotoDetailActivity.class);
                    photosIntent.putExtra("user", usersIndex);
                    photosIntent.putExtra("photo", clickedDataItem);
                    context.startActivity(photosIntent);



                    //Toast.makeText(v.getContext(), "You clicked " + clickedDataItem, Toast.LENGTH_SHORT).show();
                }
            }
        });

    }

}
// metodo set immagine dell'utente dell'imageview
private void setImage(String imageUrl, ImageView img){
    CircularProgressDrawable circularProgressDrawable =
            new CircularProgressDrawable(context);
    circularProgressDrawable.setStrokeWidth(5f);
    circularProgressDrawable.setCenterRadius(30f);
    circularProgressDrawable.start();
    GlideApp.with(context)
            .load(imageUrl)
            .placeholder(circularProgressDrawable)
            .into(img);
}

最佳答案

听到是一个主意：

首先，您应该清除列表，然后向其中添加其他数据

   yourlist.clear();
   // then add item B to your list and call adapter

范例：

      //   Items :

        Room A = new Room();
        Room B = new Room();

  //  THEN FILL A AND B ...

如下所示的填充列表，然后调用适配器：

        List<Room> roomList = new ArrayList<>();
        roomList.add(A);
        Adapter adapter = new Adapter(roomList , getContext(), this);
        recyclerView.setLayoutManager(new GridLayoutManager(getActivity() , 1));
        recyclerView.setAdapter(adapter);

我认为您没有从A项中清除列表：

        roomList.clear();
        roomList.add(B);
       // adapter.notifyDataSetChanged(); Or :
        adapter = new Adapter(roomList , getContext(), this);
        recyclerView.setLayoutManager(new GridLayoutManager(getActivity() , 1));
        recyclerView.setAdapter(adapter);