HomeFragment.java

package com.example.booksharing21;

import android.app.FragmentManager;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.nfc.Tag;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager2.adapter.FragmentViewHolder;

import android.os.Handler;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.Glide;
import com.bumptech.glide.load.model.Model;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.ChildEventListener;
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.Query;
import com.google.firebase.database.ValueEventListener;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.ListenerRegistration;
import com.google.firebase.firestore.QueryDocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;
import com.google.firebase.storage.StorageReference;
import com.squareup.picasso.Picasso;

import java.util.ArrayList;
import java.util.EventListener;
import java.util.List;

import static android.content.ContentValues.TAG;
import static com.example.booksharing21.R.id.homeFragment;
import static com.example.booksharing21.R.id.stop;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link HomeFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class HomeFragment extends Fragment  {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;
    private Object Tag;



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

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment HomeFragment.
     */
    // TODO: Rename and change types and number of parameters

    public static  HomeFragment fragment;

    public static HomeFragment newInstance(String param1, String param2) {



        if(fragment == null)
        {
            fragment = new HomeFragment();
        }


        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

    }


    public ArrayList<info> infoList ;

    public HelperAdapter helperAdapter;
    public RecyclerView inforec;
    public FirebaseFirestore db;
    public DatabaseReference mDatabase;
    public String userid = FirebaseAuth.getInstance().getCurrentUser().getUid();
    public Context mContext;



    // https://www.youtube.com/watch?v=BrDX6VTgTkg&t=617s (Retrieve data to the recycler view)

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

        View view = inflater.inflate(R.layout.fragment_home, container, false);


        // Database Reference
        db = FirebaseFirestore.getInstance();
        mDatabase = FirebaseDatabase.getInstance().getReference("posts");


        // Layout
        inforec = view.findViewById(R.id.re_view);

        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        inforec.setLayoutManager(layoutManager);
        inforec.setHasFixedSize(true);
        layoutManager.setReverseLayout(true);
        layoutManager.setStackFromEnd(true);


        // Array list
        infoList = new ArrayList<>();

        // Clear infoList
        ClearAll();

        onStart();
        onStop();


        return view;
    }



    private void ClearAll() {
        if (infoList!=null){
        infoList.clear();
        if (helperAdapter != null){
            helperAdapter.notifyDataSetChanged();
        }
        }
        infoList = new ArrayList<>();

    }


    ValueEventListener listener;

    // getting book info from db

    private void GetDataFromFirebase() {

        listener = new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                ClearAll();
                for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                    info info = new info();
                    info.setPostid(dataSnapshot.child("postid").getValue().toString());
                    info.setUrl(dataSnapshot.child("url").getValue().toString());
                    info.setBookname(dataSnapshot.child("book name").getValue().toString());
                    info.setAuthor(dataSnapshot.child("author").getValue().toString());
                    info.setIsbn(dataSnapshot.child("isbn").getValue().toString());


                    infoList.add(info);
                }

                helperAdapter = new HelperAdapter(getContext(), infoList);
                inforec.setAdapter(helperAdapter);
                helperAdapter.notifyDataSetChanged();

            }

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

                Toast.makeText(getActivity(), "No books published yet", Toast.LENGTH_LONG).show();
            }
        };

        mDatabase.addListenerForSingleValueEvent(listener);
    }



    public void database(){
        DatabaseReference connectedRef = FirebaseDatabase.getInstance().getReference(".info/connected");
        connectedRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot snapshot) {
                boolean connected = snapshot.getValue(Boolean.class);
                if (connected) {
                    System.out.println("connected");
                } else {
                    System.out.println("not connected");
                }
            }

            @Override
            public void onCancelled(DatabaseError error) {
                System.err.println("Listener was cancelled");
            }
        });


    }






    @Override
    public void onStart()
    {
        super.onStart();
        database();
        GetDataFromFirebase(); //onStart Called
    }

    public void onStop() {
        super.onStop();
        mDatabase.removeEventListener(listener);
    }

}