ListFragment.java

package com.example.padel;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;
import java.util.Comparator;


public class ListFragment extends Fragment {


    private RecyclerView recyclerView ;   //la view che mi permette di mostrare tutti gli utenti

    ArrayList<User> list = new ArrayList<>();
    MyAdapter myAdapter =new MyAdapter(list,getContext());
    FragmentManager fragmentManager;

    public ListFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_list, container, false);

        // Add the following lines to create RecyclerView
        recyclerView = view.findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(view.getContext()));
        recyclerView.setAdapter(myAdapter);

        return view;
    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        DatabaseReference database = FirebaseDatabase.getInstance("https://padel-5d8f6-default-rtdb.europe-west1.firebasedatabase.app").getReference("users");
        //recyclerView = getView().findViewById(R.id.recyclerView);
fragmentManager = getParentFragmentManager();

        database.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {


                //prendiamo tutti i dati dentro users
                for (DataSnapshot dataSnapshot : snapshot.getChildren()){

                    User user = dataSnapshot.getValue(User.class);
                    if(user.getName().compareTo("Administrator") != 0)
                       list.add(user);

                }
                list.sort(Comparator.comparing(a->a.skillValue));
                myAdapter.notifyDataSetChanged();
            }



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

            }
        });

    }


}