Recycler View - 尝试在空对象引用上调用虚拟方法“void android.widget.TextView.setText(java.lang.CharSequence)”

Question

I'm creating a app that lets you know when certain crypto currencies that you select enter your budget range in terms of price letting you know when its time to buy, for this app on the main acitivty i need a list of all the crypto currencies that i will fetch via API and for that i am using a recycler view i have created the adapted and the model class as well as the layout and i have entered a few test values to see if it would display and i get this error:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

Thank You.

Main Acitivty.java

package com.example.pricepointcrypto;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.DefaultItemAnimator;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

RecyclerView recyclerView;
CryptoCurrencyAdapter cryptoCurrencyAdapter;
ArrayList<CryptoCurrency> cryptoCurrencies = new ArrayList<>();

private String[] currencyNames = {"Bitcoin (BTC)", "Ethereal (ETH)"};
private String[] currencyRates = {"20509.88 USD" , "1174.3 USD"};
private String[] mktCap = {"3440.0%", "3235.5765%"};
private String[] totalCoins = {"3345444", "3215434"};
private String[] tradedVolume = {"4534B", "98978B"};

private int[] currencyLogos = {R.drawable.cryptocurrencylogo, R.drawable.ic_launcher_background};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    for(int i=0;i<currencyNames.length;i++)
    {
        CryptoCurrency cryptoCurrency = new CryptoCurrency();

        cryptoCurrency.setCurrencyName(currencyNames[i]);
        cryptoCurrency.setCurrentRate(currencyRates[i]);
        cryptoCurrency.setMarketCap(mktCap[i]);
        cryptoCurrency.setTotalCoins(totalCoins[i]);
        cryptoCurrency.setTradedVolume(tradedVolume[i]);

        cryptoCurrency.setCurrencyLogo(currencyLogos[i]);

        cryptoCurrencies.add(cryptoCurrency);
    }


    cryptoCurrencyAdapter = new CryptoCurrencyAdapter(cryptoCurrencies);

    recyclerView = (RecyclerView)findViewById(R.id.crypto_currencies);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(cryptoCurrencyAdapter);

}
}

CryptoCurrency.java

package com.example.pricepointcrypto;

public class CryptoCurrency {

private String currencyName;
private String currentRate;
private String marketCap;
private String totalCoins;
private String tradedVolume;

private int currencyLogo;

public int getCurrencyLogo() {
   return currencyLogo;
}

public void setCurrencyLogo(int currencyLogo) {
    this.currencyLogo = currencyLogo;
}

public String getCurrencyName() {
    return currencyName;
}

public void setCurrencyName(String currencyName) {
    this.currencyName = currencyName;
}

public String getCurrentRate() {
    return currentRate;
}

public void setCurrentRate(String currentRate) {
    this.currentRate = currentRate;
}

public String getMarketCap() {
    return marketCap;
}

public void setMarketCap(String marketCap) {
    this.marketCap = marketCap;
}

public String getTotalCoins() {
    return totalCoins;
}

public void setTotalCoins(String totalCoins) {
    this.totalCoins = totalCoins;
}

public String getTradedVolume() {
    return tradedVolume;
}

public void setTradedVolume(String tradedVolume) {
    this.tradedVolume = tradedVolume;
}
}

CryptoCurrencyAdapter.java

package com.example.pricepointcrypto;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

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

import java.util.List;

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

List<CryptoCurrency> cryptoCurrencyList;
Context context;

public CryptoCurrencyAdapter(List<CryptoCurrency> cryptoCurrencyList) {
    this.cryptoCurrencyList = cryptoCurrencyList;
}

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

@Override
public void onBindViewHolder(@NonNull CryptoCurrencyAdapter.ViewHolder holder, int position) {
    CryptoCurrency cryptoCurrency = cryptoCurrencyList.get(position);

    holder.currencyName.setText(cryptoCurrency.getCurrencyName());
    holder.currentRate.setText(cryptoCurrency.getCurrentRate());
    holder.marketCap.setText(cryptoCurrency.getMarketCap());
    holder.totalCoins.setText(cryptoCurrency.getTotalCoins());
    holder.tradedVolume.setText(cryptoCurrency.getTradedVolume());

    holder.currencyImg.setImageResource(cryptoCurrency.getCurrencyLogo());

    holder.currencyCard.setOnClickListener((View.OnClickListener) view -> Toast.makeText(context,"The position is:"+position,Toast.LENGTH_SHORT).show());

}

@Override
public int getItemCount() {
    return cryptoCurrencyList.size();
}

public class ViewHolder extends RecyclerView.ViewHolder {

    ImageView currencyImg;

    TextView currencyName;
    TextView currentRate;
    TextView marketCap;
    TextView totalCoins;
    TextView tradedVolume;

    CardView currencyCard;


    public ViewHolder(@NonNull View itemView) {
        super(itemView);

        currencyImg = itemView.findViewById(R.id.currency_logo);

        currencyName = itemView.findViewById(R.id.currency_name);
        currentRate = itemView.findViewById(R.id.current_rate);
        marketCap = itemView.findViewById(R.id.market_cap);
        totalCoins = itemView.findViewById(R.id.coin_total);
        tradedVolume = itemView.findViewById(R.id.traded_volume);

        currencyCard = itemView.findViewById(R.id.currency_card);
    }
}

}

Answer 1

Your code is working perfectly. So change crypto_card_layout. Try this and check! https://prnt.sc/jkS40DJ6nzZI

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <androidx.cardview.widget.CardView
        android:id="@+id/currency_card"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:elevation="10dp"
        app:cardCornerRadius="10dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:orientation="vertical">

            <ImageView
                android:id="@+id/currency_logo"
                android:layout_width="80dp"
                android:layout_height="80dp"
                android:layout_margin="3dp"
                android:src="@mipmap/ic_launcher" />

            <TextView
                android:id="@+id/currency_name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:textColor="@color/black"
                android:textSize="10dp" />

            <TextView
                android:id="@+id/current_rate"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:textColor="@color/black"
                android:textSize="10dp" />

            <TextView
                android:id="@+id/market_cap"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:textColor="@color/black"
                android:textSize="10dp" />

            <TextView
                android:id="@+id/coin_total"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:textColor="@color/black"
                android:textSize="10dp" />

            <TextView
                android:id="@+id/traded_volume"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:textColor="@color/black"
                android:textSize="10dp" />

        </LinearLayout>


    </androidx.cardview.widget.CardView>


</LinearLayout>