回收器视图-尝试在空对象引用上调用虚拟方法的空android.widget.TextView.setText(java.lang.CharSequence)‘

Question

我正在创建一个应用程序，让您知道您选择的某些密码货币何时按价格进入您的预算范围，让您知道何时该购买，对于这个应用程序，我需要一个通过API获取的所有密码货币的列表，为此我使用了一个回收器视图，我已经创建了经过调整的模型类以及布局，我输入了一些测试值，看看它是否会显示，并得到了这个错误：

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

谢谢。

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

你的代码运行得很好。所以改变crypto_card_layout吧。试试这个，检查一下！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>