Recyleview No Adapter attached; skipping layout error [duplicate]

Question

Trying to implement recyclerview into my project that has bottom navigation bar that has 3 item and each item has its each fragment.

But I keep getting error No adapter attached, skipping layout error.

This is my adapter

public class CategoryAdapter extends BaseAdapter {

    private List<CategoryModel> cat_list;

    public CategoryAdapter(List<CategoryModel> cat_list) {
        this.cat_list = cat_list;
    }

    @Override
    public int getCount() {
        return cat_list.size();
    }

    @Override
    public Object getItem(int i) {
        return null;
    }



@Override
    public long getItemId(int i) {
        return 0;
    }


    public View getView(int i, View view, ViewGroup viewGroup) {
        View myView;

        if (view == null){
            myView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.cat_item_layout,viewGroup,false);
        }else {
            myView = view;
        }

        TextView catName = myView.findViewById(R.id.catName);
        TextView noOfQuestion = myView.findViewById(R.id.no_of_questions);
        catName.setText(cat_list.get(i).getName());
        noOfQuestion.setText(String.valueOf(cat_list.get(i).getNoofquestions()) + " question");

        return myView;
    }

This is the main activity

bottomNavigationView = findViewById(R.id.fragment_bottom_navigation_menu_mahasiswa);
        container_frame_mahasiswa = findViewById(R.id.container_frame_mahasiswa);
        //bottomNavigationView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener);
        RecyclerView recyclerView = findViewById(R.id.mahasiswa_RecycleView);
        //catView = v.findViewById(R.id.cat_Grid);
        //adapter = new CategoryAdapter(categoryModels);
        //adapter = new CategoryAdapter(categoryModels);
        //recyclerView.setAdapter(adapter);
        //recyclerView.setLayoutManager(new LinearLayoutManager(this));
        //recyclerView.setAdapter(RecyclerView.Adapter);

as you can see I've tried a lot of stuff but it just wouldnt work

Answer 1

Try implementing your adapter like this

public class MyAdapter extends RecyclerView.Adapter<MyListAdapter.ViewHolder>{  
        private List<model> listdata;  
      
       // RecyclerView recyclerView;  
        public MyAdapter(List<model> listdata) {  
            this.listdata = listdata;  
        }  
        @Override  
        public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {  
            LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());  
            View listItem= layoutInflater.inflate(R.layout.list_item, parent, false);  
            ViewHolder viewHolder = new ViewHolder(listItem);  
            return viewHolder;  
        }  
      
        @Override  
        public void onBindViewHolder(ViewHolder holder, int position) {  
            
        }  
      
      
        @Override  
        public int getItemCount() {  
            return listdata.length;  
        }  
      
        public static class ViewHolder extends RecyclerView.ViewHolder {  
        public ViewHolder(View itemView) {  
        super(itemView);  
          
         
              }  
            }  
        }  
    } 

And Implement your code in Activity like this

RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);  
MyAdapter adapter = new MyAdapter(myListData);  
recyclerView.setHasFixedSize(true);  
recyclerView.setLayoutManager(new LinearLayoutManager(this));  
recyclerView.setAdapter(adapter);

In your viewHolder you should initialize your views like this

 public static class ViewHolder extends RecyclerView.ViewHolder {  
        public ImageView imageView;  
        public TextView textView;  
        public ViewHolder(View itemView) {  
            super(itemView);  
            this.imageView = (ImageView) itemView.findViewById(R.id.imageView);  
            this.textView = (TextView) itemView.findViewById(R.id.textView);  
              
        }  
    }  

Answer 2

Assuming we are in the Z plane with two walls, the ball would bounce right back as we have two reflections with a 45° incidence angle causing a movement change of +90° respectively.

A 'direct hit' would just result in the brown arrow being infinitely short.

This applies in dimension of you treat a corner as the conjunction point of N perpendicular walls.