我怎么知道我点击了什么回收视图 - Firebase 删除数据

Question

Hi everyone I have a question that I can't figure out about how do I know what element of the array I'm clicking in the shopping cart. So I have a shopping cart with 5 items. Each item is an object that contains (Name, Surname, Price, Key(is the key of the object inside the firebase realtime database)) and for each object, I have an ImageButton that I can click to remove that item from the cart. My problem is that I can't understand how I can know what item I'm clicking in that specific moment, because when I delete the idem I have to pass it the key and to get the key I have to know the item position in the array.

I'm attaching the Code so you can understand better. I'm new to Android and it's the first time that I'm doing this.

Thank you so much in advance.

Code :

public class CartActivity extends AppCompatActivity implements  OnRemoveItemClickListener{

    private TextView total;
    private ImageButton removeFromCart;
    private Button pay;
    private RecyclerView mResultList2;
    private DatabaseReference mUserDatabase;
    int i=0;
    int Totalprice=0;
    OnRemoveItemClickListener item;
    private RecyclerView.Adapter adapter;
    private ArrayList<Users_get> array_data = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cart);
        mUserDatabase = FirebaseDatabase.getInstance().getReference("Cart");

        total          = findViewById(R.id.TotalPrice);
        removeFromCart = findViewById(R.id.removeFromCart);
        mResultList2    = findViewById(R.id.cartList);
        pay            = findViewById(R.id.pay);

        mResultList2.setHasFixedSize(true);
        mResultList2.setLayoutManager(new LinearLayoutManager(this));


        // Attach a listener to read the data at our posts reference
        mUserDatabase.addValueEventListener(new ValueEventListener() {


            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
                    Users_get post = childSnapshot.getValue(Users_get.class);
                    array_data.add(new Users_get(post.getName(),post.getSurname(),post.getPrice(),childSnapshot.getKey()));
                    getTotalPrice(post.getPrice());
                    adapter = new UsersAdapter(array_data,item);
                    mResultList2.setAdapter(adapter);
                }
            }



            @Override
            public void onCancelled(DatabaseError databaseError) {
                System.out.println("The read failed: " + databaseError.getCode());
            }

        });

    }

    public int getTotalPrice(Long price){
        if (array_data != null) {

                Totalprice+=price;

        }System.out.println("total Price is :"+Totalprice);
        return Totalprice;
    }


    @Override
    public void onRemoveItemClicked(final int position) {
        removeFromCart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FirebaseDatabase.getInstance().getReference("Cart").child(array_data.get(position).getKey()).removeValue();
            }
        });
        adapter.notifyItemRemoved(position);
    }
}

JSON file :

    {
  "Cart" : {
    "-M0U3UXq2ZA00Jq5o9as" : {
      "name" : "Alex",
      "price" : 120,
      "surname" : "Kyto"
    },
    "-M0WlUbQHj1hdH40uWVF" : {
      "name" : "Alex",
      "price" : 120,
      "surname" : "Kyto"
    },
    "-M0WxZhI98Xb1s9Xy5HV" : {
      "name" : "Alex",
      "price" : 120,
      "surname" : "Kyto"
    },
    "-M0X00Zr64RocyQHhoFB" : {
      "name" : "Alex",
      "price" : 120,
      "surname" : "Kyto"
    }
  },
  "Users" : {
    "01" : {
      "Name" : "Alex",
      "Price" : 120,
      "Surname" : "Kyto"
    },
    "02" : {
      "Name" : "Alex",
      "Price" : 200,
      "Surname" : "Pablo"
    }
  }
}

USER ADAPTER :

     package com.example.ipill;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;


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

    private ArrayList<Users_get> cities;
    public int position;
    private OnRemoveItemClickListener mListener;
    public UsersAdapter(ArrayList<Users_get> cities,OnRemoveItemClickListener listener) {
        this.cities = cities;
        this.mListener = listener;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = (View) LayoutInflater.from(parent.getContext()).inflate(R.layout.list_layout_cart, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {
        final Users_get city = cities.get(position);
        holder.name.setText(city.getName());
        holder.surname.setText(city.getSurname());
        holder.price.setText(Long.toString(city.getPrice()));

    }

    @Override
    public int getItemCount() {
        if (cities != null) {
            return cities.size();
        } else {
            return 0;
        }
    }

    public  class ViewHolder extends RecyclerView.ViewHolder {
        public final View view;
        public final TextView name;
        public final TextView surname;
        public final TextView price;
        public final ImageButton removee;


        public ViewHolder(View view) {
            super(view);
            this.view = view;
            name = view.findViewById(R.id.name2);
            surname = view.findViewById(R.id.Surname2);
            price = view.findViewById(R.id.Price2);
            removee = view.findViewById(R.id.removeFromCart);

            removee.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    mListener.onRemoveItemClicked(ViewHolder.this.getAdapterPosition());
                }
            });

        }
    }
}

Error : java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.ipill.OnRemoveItemClickListener.onRemoveItemClicked(int)' on a null object reference

Since the Image button is create when the objects inside the recycle view are created.

Answer 1

I have changed the required thing, like passing listener from activity to adapter then callback from adapter,

Create 1 interface,

public IItemClick{
 public void onItemClick (String key, int position)
}

Activity Class

public class CartActivity extends AppCompatActivity implements IItemClick {

     // change  
    public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
                    Users_get post = childSnapshot.getValue(Users_get.class);
                    array_data.add(new Users_get(post.getName(),post.getSurname(),post.getPrice(),childSnapshot.getKey()));
                    adapter = new UsersAdapter(array_data, this);
                    mResultList2.setAdapter(adapter);
                }
            }


                override public void onItemClick(String key, int position){
                 // perform your delete operation from firebase here
                 // after delete  
                adapter.notifyItemRemoved(position)
                }

        }

Adapter Code

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

    private ArrayList<Users_get> cities;
    public int position;
    IItemClick listener;
    public UsersAdapter(ArrayList<Users_get> cities,IItemClick listener ) {
        this.cities = cities;
        this.listener = listener
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = (View) LayoutInflater.from(parent.getContext()).inflate(R.layout.list_layout_cart, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Users_get city = cities.get(position);
        holder.name.setText(city.getName());
        holder.surname.setText(city.getSurname());
        holder.price.setText(Long.toString(city.getPrice()));
        holder.name.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
         listener.onItemClick(city.getKey(), position);
        }

    }

    @Override
    public int getItemCount() {
        if (cities != null) {
            return cities.size();
        } else {
            return 0;
        }
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public final View view;
        public final TextView name;
        public final TextView surname;
        public final TextView price;


        public ViewHolder(View view) {
            super(view);
            this.view = view;
            name = view.findViewById(R.id.name_text2);
            surname = view.findViewById(R.id.status_text2);
            price = view.findViewById(R.id.price2);
    }
}

Answer 2

Please follow step by step procedure:

1) I'm considering that you have the Image Button in your R.layout.list_layout_cart , now find that ImageButton by FindViewById() method in your ViewHolder class in UserAdapter (Here please keep the ViewHolder class non-static).

So here is your UserAdapter

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

private ArrayList<Users_get> cities;
public int position;

private OnRemoveItemClickListener mListener;

public UsersAdapter(ArrayList<Users_get> cities, OnRemoveItemClickListener listener) {
    this.cities = cities;

    this.mListener = listener;
}

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View v = (View) LayoutInflater.from(parent.getContext()).inflate(R.layout.list_layout_cart, parent, false);
    return new ViewHolder(v);
}

@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
    Users_get city = cities.get(position);
    holder.name.setText(city.getName());
    holder.surname.setText(city.getSurname());
    holder.price.setText(Long.toString(city.getPrice()));

}

@Override
public int getItemCount() {
    if (cities != null) {
        return cities.size();
    } else {
        return 0;
    }
}

public class ViewHolder extends RecyclerView.ViewHolder {
    public final View view;
    public final TextView name;
    public final TextView surname;
    public final TextView price;

    public Button mImageButton;


    public ViewHolder(View view) {
        super(view);
        this.view = view;
        name = view.findViewById(R.id.name_text2);
        surname = view.findViewById(R.id.status_text2);
        price = view.findViewById(R.id.price2);

        mImageButton = view.findViewById(R.id.btn_img_remove);

        mImageButton.setOnClickListener(v -> {
            if(mListener != null) {
                 mListener.onRemoveItemClicked(getAdapterPosition()));
             }
        });

    }
}
}

2) Create an Interface like this

public interface OnRemoveItemClickListener{
    void onRemoveItemClicked(int position);
}

3) Now Just Implement the Interface in your Activity and handle the item removal from Array in your Activity