我正在创建一个名为Pricepointcrypto的应用程序，其中当您感兴趣的某种加密货币击中您的预算范围时，您将得到通知说您想购买比特币15,000股票市场命中，您将得到通知，在这个应用程序中，我需要显示加密货币及其利率，我正在使用coinmarketcap API用于android studio with java。我已经在java中创建了请求和响应功能，它确实在后台工作，但我在循环视图上有一个布局问题，当它尝试顶部渲染时，当我们想要setText时，它说它为空
下面是我得到的错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
我只是停留在这部分，我已经尝试了许多测试，所以如果有人可以帮助它将是非常有用的
谢谢!
代码如下:
主要Acitivty.java
package com.example.pricepointcrypto;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
public class MainActivity extends AppCompatActivity {
private ArrayList<CurrencyModal> currencyModalArrayList;
private CurrencyRVAdapter currencyRVAdapter;
private ProgressBar loadingPB;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
EditText searchEdt = findViewById(R.id.idEdtCurrency);
// initializing all our variables and array list.
loadingPB = findViewById(R.id.idPBLoading);
// creating variable for recycler view,
// adapter, array list, progress bar
RecyclerView currencyRV = findViewById(R.id.idRVcurrency);
currencyModalArrayList = new ArrayList<>();
// initializing our adapter class.
currencyRVAdapter = new CurrencyRVAdapter(currencyModalArrayList, this);
// setting layout manager to recycler view.
currencyRV.setLayoutManager(new LinearLayoutManager(this));
// setting adapter to recycler view.
currencyRV.setAdapter(currencyRVAdapter);
// calling get data method to get data from API.
getData();
// on below line we are adding text watcher for our
// edit text to check the data entered in edittext.
searchEdt.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}
@Override
public void afterTextChanged(Editable s) {
// on below line calling a
// method to filter our array list
filter(s.toString());
}
});
}
private void filter(String filter) {
// on below line we are creating a new array list
// for storing our filtered data.
ArrayList<CurrencyModal> filteredlist = new ArrayList<>();
// running a for loop to search the data from our array list.
for (CurrencyModal item : currencyModalArrayList) {
// on below line we are getting the item which are
// filtered and adding it to filtered list.
if (item.getName().toLowerCase().contains(filter.toLowerCase())) {
filteredlist.add(item);
}
}
// on below line we are checking
// weather the list is empty or not.
if (filteredlist.isEmpty()) {
// if list is empty we are displaying a toast message.
Toast.makeText(this, "No currency found..", Toast.LENGTH_SHORT).show();
} else {
// on below line we are calling a filter
// list method to filter our list.
currencyRVAdapter.filterList(filteredlist);
}
}
private void getData() {
// creating a variable for storing our string.
String url = "https://pro-api.coinmarketcap.com/v1/cryptocurrency/listings/latest";
// creating a variable for request queue.
RequestQueue queue = Volley.newRequestQueue(this);
// making a json object request to fetch data from API.
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null,
response -> {
// inside on response method extracting data
// from response and passing it to array list
// on below line we are making our progress
// bar visibility to gone.
loadingPB.setVisibility(View.GONE);
try {
// extracting data from json.
JSONArray dataArray = response.getJSONArray("data");
for (int i = 0; i < dataArray.length(); i++) {
JSONObject dataObj = dataArray.getJSONObject(i);
String symbol = dataObj.getString("symbol");
String name = dataObj.getString("name");
JSONObject quote = dataObj.getJSONObject("quote");
JSONObject USD = quote.getJSONObject("USD");
double price = USD.getDouble("price");
String finalName = ""+name+" - "+symbol+"";
// adding all data to our array list.
currencyModalArrayList.add(new CurrencyModal(finalName,
R.drawable.ic_launcher_foreground, price));
}
// notifying adapter on data change.
currencyRVAdapter.notifyDataSetChanged();
} catch (JSONException e) {
// handling json exception.
e.printStackTrace();
Toast.makeText(MainActivity.this, "Something went amiss. Please try again later",
Toast.LENGTH_SHORT).show();
}
}, error -> {
// displaying error response when received any error.
Toast.makeText(MainActivity.this, "Something went amiss. Please try again later",
Toast.LENGTH_SHORT).show();
}) {
@Override
public Map<String, String> getHeaders() {
// in this method passing headers as
// key along with value as API keys.
HashMap<String, String> headers = new HashMap<>();
headers.put("X-CMC_PRO_API_KEY", "106d7841-b282-4c8c-aa0f-d53509398468");
// at last returning headers
return headers;
}
};
// calling a method to add our
// json object request to our queue.
queue.add(jsonObjectRequest);
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/blac_shade_1"
tools:context=".MainActivity">
<!--edit text for searching our currency-->
<EditText
android:id="@+id/idEdtCurrency"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="8dp"
android:focusable="auto"
android:hint="Search Currency"
android:textColor="@color/white"
android:textColorHint="@color/white" />
<!--recycler view for displaying the list of currencies-->
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/idRVcurrency"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/idEdtCurrency"
tools:listitem="@layout/crypto_card_layout" />
<!--progress bar for loading indicator-->
<ProgressBar
android:id="@+id/idPBLoading"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:visibility="gone" />
</RelativeLayout>
CurrencyRVApdapter
package com.example.pricepointcrypto;
import android.annotation.SuppressLint;
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 androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.text.DecimalFormat;
import java.util.ArrayList;
// on below line we are creating our adapter class
// in this class we are passing our array list
// and our View Holder class which we have created.
public class CurrencyRVAdapter extends
RecyclerView.Adapter<CurrencyRVAdapter.CurrencyViewholder> {
private static DecimalFormat df2 = new DecimalFormat("#.##");
private ArrayList<CurrencyModal> currencyModals;
private Context context;
public CurrencyRVAdapter(ArrayList<CurrencyModal> currencyModals, Context context) {
this.currencyModals = currencyModals;
this.context = context;
}
// below is the method to filter our list.
public void filterList(ArrayList<CurrencyModal> filterllist) {
// adding filtered list to our
// array list and notifying data set changed
currencyModals = filterllist;
notifyDataSetChanged();
}
@NonNull
@Override
public CurrencyRVAdapter.CurrencyViewholder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
// this method is use to inflate the layout file
// which we have created for our recycler view.
// on below line we are inflating our layout file.
View view = LayoutInflater.from(context).inflate(R.layout.crypto_card_layout , parent, false);
return new CurrencyViewholder(view);
}
@SuppressLint("SetTextI18n")
@Override
public void onBindViewHolder(@NonNull CurrencyRVAdapter.CurrencyViewholder holder, int position) {
// on below line we are setting data to our item of
// recycler view and all its views.
CurrencyModal modal = currencyModals.get(position);
holder.nameTV.setText(modal.getName());
holder.rateTV.setText("$ " + df2.format(modal.getPrice()) + " USD");
holder.symbolTV.setImageResource(modal.getSymbol());
}
@Override
public int getItemCount() {
// on below line we are returning
// the size of our array list.
return currencyModals.size();
}
// on below line we are creating our view holder class
// which will be used to initialize each view of our layout file.
public class CurrencyViewholder extends RecyclerView.ViewHolder {
private ImageView symbolTV;
private TextView rateTV, nameTV;
public CurrencyViewholder(@NonNull View itemView) {
super(itemView);
// on below line we are initializing all
// our text views along with its ids.
symbolTV = itemView.findViewById(R.id.currency_logo);
rateTV = itemView.findViewById(R.id.currency_Rate);
nameTV = itemView.findViewById(R.id.currency_name);
}
}
}
CurrencyModal
package com.example.pricepointcrypto;
public class CurrencyModal {
// variable for currency name,
// currency symbol and price.
private String name;
private int symbol;
private double price;
public CurrencyModal(String name, int symbol, double price) {
this.name = name;
this.symbol = symbol;
this.price = price;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getSymbol() {
return symbol;
}
public void setSymbol(int symbol) {
this.symbol = symbol;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
}
crypto_card_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
>
<androidx.cardview.widget.CardView
android:id="@+id/currency_card"
android:layout_width="match_parent"
android:layout_height="wrap_content"
card_view:cardBackgroundColor="#03A9F4"
card_view:cardCornerRadius="20dp"
card_view:cardElevation="5dp"
card_view:cardUseCompatPadding="true">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<ImageView
android:id="@+id/currency_logo"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:layout_weight="1"
android:src="@drawable/ic_launcher_foreground"
android:tag="image_tag"
android:contentDescription="@string/currencylogo" />
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginTop="12dp"
android:layout_weight="2"
android:orientation="vertical">
<TextView
android:id="@+id/currency_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="start|center_horizontal"
android:layout_marginTop="10dp"
android:fontFamily="casual"
android:text="Currency Name"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textColor="#FFEB3B"
android:textStyle="bold" />
<TextView
android:id="@+id/currency_Rate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="start|center_horizontal"
android:layout_marginTop="0dp"
android:fontFamily="@font/stick"
android:text="Current Rate: "
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#FFFFFF"
android:textColorHighlight="#FFFFFF"
android:textStyle="bold|italic" />
</LinearLayout>
</LinearLayout>
</androidx.cardview.widget.CardView>
</LinearLayout>
View view = LayoutInflater.from(context).inflate(R.layout.crypto_card_layout , parent, false);
尝试设置LayoutInflater.from(parent.getContext())而不是LayoutInflater.from(context)