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  • 尝试用JSON填充微调器并获得'；java.lang.Object[]java.util.Collection.toArray（）'；关于空对象引用

尝试用JSON填充微调器并获得'；java.lang.Object[]java.util.Collection.toArray（）'；关于空对象引用

java android json

尝试用JSON填充微调器并获得'；java.lang.Object[]java.util.Collection.toArray（）'；关于空对象引用,java,android,json,nullpointerexception,android-spinner,Java,Android,Json,Nullpointerexception,Android Spinner,我是一个android新手，正在尝试使用JSON填充spinner，但我一直遇到空指针异常- java.lang.NullPointerException: Attempt to invoke interface method java.lang.Object[] java.util.Collection.toArray()' on a null object reference 我知道这是一个常见的问题，我已经看过了其他的答案和解决方案。我已尝试初始化列表，但仍然无法修复错误。我想

我是一个android新手，正在尝试使用JSON填充spinner，但我一直遇到空指针异常-

  java.lang.NullPointerException: Attempt to invoke interface method
  java.lang.Object[] java.util.Collection.toArray()' on a null object
 reference
我知道这是一个常见的问题，我已经看过了其他的答案和解决方案。我已尝试初始化列表，但仍然无法修复错误。我想我在理解确切需要初始化的位置时遇到了问题

我的完整日志：

07-19 09:34:54.356 11199-11337/com.genx.meghna.makdver4 D/Result is: [{"car_number":"DL 2345"},{"car_number":"DL 53546"},{"car_number":"1472"},{"car_number":"m7894"},{"car_number":"nxjvjsv"}]
07-19 09:34:54.356 11199-11337/com.genx.meghna.makdver4 D/res =: [{"car_number":"DL 2345"},{"car_number":"DL 53546"},{"car_number":"1472"},{"car_number":"m7894"},{"car_number":"nxjvjsv"}]
07-19 09:34:54.357 11199-11337/com.genx.meghna.makdver4 E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #3
   Process: com.genx.meghna.makdver4, PID: 11199
   java.lang.RuntimeException: An error occured while executing doInBackground()
       at android.os.AsyncTask$3.done(AsyncTask.java:300)
       at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
       at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
       at java.util.concurrent.FutureTask.run(FutureTask.java:242)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
       at java.lang.Thread.run(Thread.java:818)
    Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object[] java.util.Collection.toArray()' on a null object reference
       at java.util.ArrayList.addAll(ArrayList.java:188)
       at com.genx.meghna.makdver4.Fragments.SendCarFragment$GetData.doInBackground(SendCarFragment.java:173)
       at com.genx.meghna.makdver4.Fragments.SendCarFragment$GetData.doInBackground(SendCarFragment.java:117)
       at android.os.AsyncTask$2.call(AsyncTask.java:288)
       at java.util.concurrent.FutureTask.run(FutureTask.java:237)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
       at java.lang.Thread.run(Thread.java:818) 

package com.genx.meghna.makdver4.Fragments;


import android.content.Context;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.genx.meghna.makdver4.R;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import static com.genx.meghna.makdver4.Fragments.LoginFragment.un;


public class SendCarFragment extends Fragment {

    TextView tv1, tv2, tv3;
    Spinner sp;
    RadioGroup rg;
    RadioButton rb1, rb2;
    Button btn;
    FragmentManager fm;
    ArrayList<String> carList;
    ArrayAdapter<String> adapter;
    String res;
    SharedPreferences spp;


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


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_send_car, container, false);
        btn = rootView.findViewById(R.id.nextPage1);
        rg = rootView.findViewById(R.id.radioGroup1);
        rb1 = rootView.findViewById(R.id.rb1);
        rb2 = rootView.findViewById(R.id.rb2);

        sp = rootView.findViewById(R.id.spinnerSelectCar);

        spp=getContext().getSharedPreferences("MyPrefs", Context.MODE_PRIVATE);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (rg.getCheckedRadioButtonId() == -1) {
                    Toast.makeText(getContext(), "Select One Option", Toast.LENGTH_SHORT).show();
                } else {
                    if (rb1.isChecked()) {
                        fm = getFragmentManager();
                        fm.beginTransaction().replace(R.id.container, new ServiceCenterListFragment(), "Service center").commit();

                    } else {

                        fm = getFragmentManager();
                        fm.beginTransaction().replace(R.id.container, new SelectionFragment(), "Select Address").commit();
                    }
                }
            }
        });

        return rootView;
    }

   public void onStart(){
        super.onStart();
        String username1 = spp.getString(un, "userKey");
        GetData get = new GetData();
        get.execute(username1);
    }

    class GetData extends AsyncTask<String, Void, String> {
      List<String> list;
       protected void onPreExecute(){
            super.onPreExecute();
            list=new ArrayList<>();
        }

        @Override
        protected String doInBackground(String... params) {
            {
                try {
                    String username1 = params[0];

                    String link = "http://10.0.3.2//Traccar/getCars.php";
                    String myurl = "username=" + username1;
                    URL url = new URL(link);
                    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("POST");
                    connection.getOutputStream().write(myurl.getBytes());
                    int response = connection.getResponseCode();
                    Log.d("Response code", "" + response);

                    if (response == HttpURLConnection.HTTP_OK) {
                        String line;
                        InputStreamReader isr = new InputStreamReader(connection.getInputStream());
                        BufferedReader br = new BufferedReader(isr);
                        StringBuilder buffer = new StringBuilder();
                        while ((line = br.readLine()) != null) {
                            buffer.append(line);
                            //res+=line;
                        }

                        Log.d("Result is", buffer.toString());
                        res = buffer.toString();
                        Log.d("res = ", res);
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            try{
                JSONArray jrr =  new JSONArray(res);
                for (int i=0; i<jrr.length(); i++) {
                    JSONObject obj = jrr.getJSONObject(i);
                    String name = obj.getString("car_number");
                    list.add(name);
                }
            } catch (JSONException e1) {
                e1.printStackTrace();
            }

            return res;
        }


        protected void onPostExecute(String res) {

            list.addAll(carList);
            adapter = new ArrayAdapter<>(getContext(),android.R.layout.simple_list_item_1, carList);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            sp.setAdapter(adapter);


        }
    }
}
我的代码：

07-19 09:34:54.356 11199-11337/com.genx.meghna.makdver4 D/Result is: [{"car_number":"DL 2345"},{"car_number":"DL 53546"},{"car_number":"1472"},{"car_number":"m7894"},{"car_number":"nxjvjsv"}]
07-19 09:34:54.356 11199-11337/com.genx.meghna.makdver4 D/res =: [{"car_number":"DL 2345"},{"car_number":"DL 53546"},{"car_number":"1472"},{"car_number":"m7894"},{"car_number":"nxjvjsv"}]
07-19 09:34:54.357 11199-11337/com.genx.meghna.makdver4 E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #3
   Process: com.genx.meghna.makdver4, PID: 11199
   java.lang.RuntimeException: An error occured while executing doInBackground()
       at android.os.AsyncTask$3.done(AsyncTask.java:300)
       at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
       at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
       at java.util.concurrent.FutureTask.run(FutureTask.java:242)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
       at java.lang.Thread.run(Thread.java:818)
    Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object[] java.util.Collection.toArray()' on a null object reference
       at java.util.ArrayList.addAll(ArrayList.java:188)
       at com.genx.meghna.makdver4.Fragments.SendCarFragment$GetData.doInBackground(SendCarFragment.java:173)
       at com.genx.meghna.makdver4.Fragments.SendCarFragment$GetData.doInBackground(SendCarFragment.java:117)
       at android.os.AsyncTask$2.call(AsyncTask.java:288)
       at java.util.concurrent.FutureTask.run(FutureTask.java:237)
       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
       at java.lang.Thread.run(Thread.java:818) 

package com.genx.meghna.makdver4.Fragments;


import android.content.Context;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.genx.meghna.makdver4.R;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import static com.genx.meghna.makdver4.Fragments.LoginFragment.un;


public class SendCarFragment extends Fragment {

    TextView tv1, tv2, tv3;
    Spinner sp;
    RadioGroup rg;
    RadioButton rb1, rb2;
    Button btn;
    FragmentManager fm;
    ArrayList<String> carList;
    ArrayAdapter<String> adapter;
    String res;
    SharedPreferences spp;


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


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_send_car, container, false);
        btn = rootView.findViewById(R.id.nextPage1);
        rg = rootView.findViewById(R.id.radioGroup1);
        rb1 = rootView.findViewById(R.id.rb1);
        rb2 = rootView.findViewById(R.id.rb2);

        sp = rootView.findViewById(R.id.spinnerSelectCar);

        spp=getContext().getSharedPreferences("MyPrefs", Context.MODE_PRIVATE);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (rg.getCheckedRadioButtonId() == -1) {
                    Toast.makeText(getContext(), "Select One Option", Toast.LENGTH_SHORT).show();
                } else {
                    if (rb1.isChecked()) {
                        fm = getFragmentManager();
                        fm.beginTransaction().replace(R.id.container, new ServiceCenterListFragment(), "Service center").commit();

                    } else {

                        fm = getFragmentManager();
                        fm.beginTransaction().replace(R.id.container, new SelectionFragment(), "Select Address").commit();
                    }
                }
            }
        });

        return rootView;
    }

   public void onStart(){
        super.onStart();
        String username1 = spp.getString(un, "userKey");
        GetData get = new GetData();
        get.execute(username1);
    }

    class GetData extends AsyncTask<String, Void, String> {
      List<String> list;
       protected void onPreExecute(){
            super.onPreExecute();
            list=new ArrayList<>();
        }

        @Override
        protected String doInBackground(String... params) {
            {
                try {
                    String username1 = params[0];

                    String link = "http://10.0.3.2//Traccar/getCars.php";
                    String myurl = "username=" + username1;
                    URL url = new URL(link);
                    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("POST");
                    connection.getOutputStream().write(myurl.getBytes());
                    int response = connection.getResponseCode();
                    Log.d("Response code", "" + response);

                    if (response == HttpURLConnection.HTTP_OK) {
                        String line;
                        InputStreamReader isr = new InputStreamReader(connection.getInputStream());
                        BufferedReader br = new BufferedReader(isr);
                        StringBuilder buffer = new StringBuilder();
                        while ((line = br.readLine()) != null) {
                            buffer.append(line);
                            //res+=line;
                        }

                        Log.d("Result is", buffer.toString());
                        res = buffer.toString();
                        Log.d("res = ", res);
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            try{
                JSONArray jrr =  new JSONArray(res);
                for (int i=0; i<jrr.length(); i++) {
                    JSONObject obj = jrr.getJSONObject(i);
                    String name = obj.getString("car_number");
                    list.add(name);
                }
            } catch (JSONException e1) {
                e1.printStackTrace();
            }

            return res;
        }


        protected void onPostExecute(String res) {

            list.addAll(carList);
            adapter = new ArrayAdapter<>(getContext(),android.R.layout.simple_list_item_1, carList);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            sp.setAdapter(adapter);


        }
    }
}

package com.genx.meghna.makdver4.Fragments；
导入android.content.Context；
导入android.content.SharedReferences；
导入android.os.AsyncTask；
导入android.os.Bundle；
导入android.support.v4.app.Fragment；
导入android.support.v4.app.FragmentManager；
导入android.util.Log；
导入android.view.LayoutInflater；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.ArrayAdapter；
导入android.widget.Button；
导入android.widget.RadioButton；
导入android.widget.RadioGroup；
导入android.widget.Spinner；
导入android.widget.TextView；
导入android.widget.Toast；
导入com.genx.meghna.makdver4.R；
导入org.json.JSONArray；
导入org.json.JSONException；
导入org.json.JSONObject；
导入java.io.BufferedReader；
导入java.io.IOException；
导入java.io.InputStreamReader；
导入java.net.HttpURLConnection；
导入java.net.MalformedURLException；
导入java.net.URL；
导入java.util.ArrayList；
导入java.util.List；
导入静态com.genx.meghna.makdver4.Fragments.LoginFragment.un；
公共类SendCarFragment扩展了片段{
文本视图tv1、tv2、tv3；
纺纱机；
放射组rg；
单选按钮rb1、rb2；
按钮btn；
碎片管理器fm；
ArrayList carList；
阵列适配器；
字符串res；
共享参考资料；
公共SendCarFragment（）{
//必需的空公共构造函数
}
@凌驾
创建视图上的公共视图（布局、充气机、视图组容器、，
Bundle savedInstanceState）{
//为该碎片膨胀布局
视图根视图=充气机。充气（R.layout.fragment\u send\u car，container，false）；
btn=rootView.findviewbyd（R.id.nextPage1）；
rg=rootView.findviewbyd（R.id.1）；
rb1=rootView.findviewbyd（R.id.rb1）；
rb2=rootView.findviewbyd（R.id.rb2）；
sp=rootView.findviewbyd（R.id.spinnerSelectCar）；
spp=getContext（）.getSharedReferences（“MyPrefs”，Context.MODE\u PRIVATE）；
btn.setOnClickListener（新视图.OnClickListener（）{
@凌驾
公共void onClick（视图）{
if（rg.getCheckedRadioButtonId（）=-1）{
Toast.makeText（getContext（），“选择一个选项”，Toast.LENGTH_SHORT.show（）；
}否则{
if（rb1.isChecked（））{
fm=getFragmentManager（）；
fm.beginTransaction（）.replace（R.id.container，新ServiceCenterListFragment（），“服务中心”）.commit（）；
}否则{
fm=getFragmentManager（）；
fm.beginTransaction（）.replace（R.id.container，new SelectionFragment（），“Select Address”）.commit（）；
}
}
}
});
返回rootView；
}
public void onStart（）{
super.onStart（）；
字符串username1=spp.getString（un，“userKey”）；
GetData get=新建GetData（）；
get.execute（username1）；
}
类GetData扩展异步任务{
名单；
受保护的void onPreExecute（）{
super.onPreExecute（）；
列表=新的ArrayList（）；
}
@凌驾
受保护的字符串doInBackground（字符串…参数）{
{
试一试{
字符串username1=params[0]；
字符串链接=”http://10.0.3.2//Traccar/getCars.php";
字符串myurl=“username=”+username1；
URL=新的URL（链接）；
HttpURLConnection connection=（HttpURLConnection）url.openConnection（）；
connection.setRequestMethod（“POST”）；
connection.getOutputStream（）.write（myurl.getBytes（））；
int response=connection.getResponseCode（）；
Log.d（“响应代码”，“响应+响应”）；
if（response==HttpURLConnection.HTTP\u OK）{
弦线；
InputStreamReader isr=新的InputStreamReader（connection.getInputStream（））；
BufferedReader br=新的BufferedReader（isr）；
StringBuilder缓冲区=新的StringBuilder（）；
而（（line=br.readLine（））！=null）{
buffer.append（行）；
//res+=直线；
}
Log.d（“结果是”，buffer.toString（））；
res=buffer.toString（）；
Log.d（“res=”，res）；
}
}捕获（格式错误）{
e、 printStackTrace（）；
}捕获（IOE异常）{
e、 printStackTrace（）；
}
}
试一试{
JSONArray jrr=新JSONArray（res）；

对于（int i=0；i您有一个
carList
和一个
list
。您不会初始化或向
carList
添加项目，而是尝试将其传递给
list.addAll（carList）；
，这自然无法工作

由于数据已经在
列表中
您应该能够这样做


class GetData extends AsyncTask<String, Void, List<String>> {
   List<String> list;

   protected void onPreExecute(){
        super.onPreExecute();
        list=new ArrayList<>();
    }

    @Override
    protected String doInBackground(String... params) {
        {
            try {
                String username1 = params[0];

                String link = "http://10.0.3.2//Traccar/getCars.php";
                String myurl = "username=" + username1;
                URL url = new URL(link);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("POST");
                connection.getOutputStream().write(myurl.getBytes());
                int response = connection.getResponseCode();
                Log.d("Response code", "" + response);

                if (response == HttpURLConnection.HTTP_OK) {
                    String line;
                    InputStreamReader isr = new InputStreamReader(connection.getInputStream());
                    BufferedReader br = new BufferedReader(isr);
                    StringBuilder buffer = new StringBuilder();
                    while ((line = br.readLine()) != null) {
                        buffer.append(line);
                        //res+=line;
                    }

                    Log.d("Result is", buffer.toString());
                    res = buffer.toString();
                    Log.d("res = ", res);
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        try{
            JSONArray jrr =  new JSONArray(res);
            for (int i=0; i<jrr.length(); i++) {
                JSONObject obj = jrr.getJSONObject(i);
                String name = obj.getString("car_number");
                list.add(name);
            }
        } catch (JSONException e1) {
            e1.printStackTrace();
        }

        return list;
    }


    protected void onPostExecute(List<String> res) {

        adapter = new ArrayAdapter<>(getContext(),android.R.layout.simple_list_item_1, res);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        sp.setAdapter(adapter);


    }
}



class GetData扩展异步任务{
名单；
受保护的void onPreExecute（）{
super.onPreExecute（）；
列表=新的ArrayList（）；
}
@凌驾
受保护字符串