了java.lang.RuntimeException：在執行doInBackground（）URI時出錯

Question

我是新到Android編程 我試圖編寫代碼的應用程序 我試圖使用URI 但它一直給下面的錯誤 尋求幫助

的java文件

package com.example.ayushspc.digilocker; 

import android.os.AsyncTask; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.widget.Toast; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 
import org.w3c.dom.Text; 

import java.io.BufferedWriter; 
import java.io.IOException; 
import java.io.OutputStream; 
import java.io.OutputStreamWriter; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
import java.net.URLEncoder; 

public class GetRegDetails extends AppCompatActivity { 
    Register register = new Register(); 
    EditText ET_MOBILE, ET_EMAIL; 
    String json_string; 
    JSONArray jsonArray; 
    JSONObject jsonObject; 
    String name, branch, email, mobile, enroll, OTP; 
    OTPGenerator otpGenerator; 
    Sendsms sendsms; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     otpGenerator = new OTPGenerator(); 
     sendsms = new Sendsms(); 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_get_reg_details); 

     enroll = register.enroll; 
     json_string = getIntent().getExtras().getString("jsonresult"); 

     try { 
      jsonObject = new JSONObject(json_string); 
      jsonArray = jsonObject.getJSONArray("server_response"); 
      int count = 0; 
      while (count < jsonArray.length()) { 
       JSONObject JO = jsonArray.getJSONObject(count); 
       name = JO.getString("name"); 
       branch = JO.getString("branch"); 
       count++; 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 

     TextView tv_name = (TextView) findViewById(R.id.ver_name); 
     TextView tv_branch = (TextView) findViewById(R.id.ver_branch); 
     tv_name.setText(name); 
     tv_name.setVisibility(View.VISIBLE); 
     tv_branch.setText(branch); 
     tv_branch.setVisibility(View.VISIBLE); 

    } 

    public void verifyDetails(View view) { 
     ET_MOBILE = (EditText) findViewById(R.id.ver_mobile); 
     ET_EMAIL = (EditText) findViewById(R.id.ver_email); 
     mobile = ET_MOBILE.getText().toString(); 
     email = ET_EMAIL.getText().toString(); 
     OTP = otpGenerator.generator(); 
     String number = mobile.toString(); 
     // sendsms.message(number, OTP);//add enrollment number to message;pass mesage as an argument 
     Toast.makeText(getApplicationContext(), mobile + " " + OTP, Toast.LENGTH_SHORT).show(); 
     new BackgroundTask().execute(enroll, mobile, email, OTP); 
     Toast.makeText(getApplicationContext(), OTP, Toast.LENGTH_LONG).show(); 

    } 

    class BackgroundTask extends AsyncTask<String, Void, String> { 
     String otp_url = "http://www.digiloc.esy.es/otp_verification.php"; 

     @Override 
     protected String doInBackground(String... params) { 
      String enrollment, mobile, email, otp; 
      enrollment = params[0]; 
      mobile = params[1]; 
      email = params[2]; 
      otp = params[3]; 

      try { 
       URL url = new URL(otp_url); 
       HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); 
       httpURLConnection.setRequestMethod("POST"); 
       httpURLConnection.setDoOutput(true); 
       OutputStream outputStream = httpURLConnection.getOutputStream(); 
       BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8")); 
       String data = URLEncoder.encode("enroll", "UTF-8") + "=" + URLEncoder.encode(enrollment, "UTF-8") + "&" + 
         URLEncoder.encode("mobile", "UTF-8") + "=" + URLEncoder.encode(mobile, "UTF-8") + "&" + 
         URLEncoder.encode("email", "UTF-8") + "=" + URLEncoder.encode(email, "UTF-8") + "&" + 
         URLEncoder.encode("otp", "UTF-8") + "=" + URLEncoder.encode(otp, "UTF-8"); 
       bufferedWriter.write(data); 
       bufferedWriter.flush(); 
       bufferedWriter.close(); 
       outputStream.close(); 

      } catch (MalformedURLException e) { 
       e.printStackTrace(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } 

      return null; 
     } 
    } 
} 

日誌文件

02-06 22:12:05.140 11850-12852/com.example.ayushspc.digilocker E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #4 
    java.lang.RuntimeException: An error occured while executing doInBackground() 
      at android.os.AsyncTask$3.done(AsyncTask.java:299) 
      at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273) 
      at java.util.concurrent.FutureTask.setException(FutureTask.java:124) 
      at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307) 
      at java.util.concurrent.FutureTask.run(FutureTask.java:137) 
      at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 
      at java.lang.Thread.run(Thread.java:864) 
    Caused by: java.lang.NullPointerException 
      at libcore.net.UriCodec.encode(UriCodec.java:132) 
      at java.net.URLEncoder.encode(URLEncoder.java:57) 
      at com.example.ayushspc.digilocker.GetRegDetails$BackgroundTask.doInBackground(GetRegDetails.java:102) 
      at com.example.ayushspc.digilocker.GetRegDetails$BackgroundTask.doInBackground(GetRegDetails.java:84) 
      at android.os.AsyncTask$2.call(AsyncTask.java:287) 
      at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 
            at java.util.concurrent.FutureTask.run(FutureTask.java:137) 
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 
            at java.lang.Thread.run(Thread.java:864) 
02-06 22:12:05.400 11850-11850/com.example.ayushspc.digilocker E/copybit﹕ Error opening frame buffer errno=13 (Permission denied) 

能有人可能指出錯誤 的原因，也有辦法解決呢

Answer 1

enroll = register.enroll; 

register.enroll返回null。顯示Register課程或嘗試自行找出問題。