android没有从mysql数据库

Question

我目前正在开发一个Android项目，允许用户从数据库添加/更新/读取和删除记录。应用程序现在运行时没有任何错误，但是当我点击插入新记录或查看所有员工记录时，它只返回空白页面？我不认为它可以访问PHP文件或可能是其他任何东西？我有一个Config.java文件，其中我的php文件的地址上传到我的大学mudfoot服务器和一个ViewAllEmployee.java文件，当执行onClick时调用该文件应该使用JSON从我的数据库返回结果。任何人都可以指出我正确的方向如何纠正这一点，我一直在尝试最后几个小时，但似乎无法弄明白。

Config.java

package com.example.assignment.androidassignment;

public class Config {

//Address of our scripts of the CRUD
public static final String URL_ADD="http://www.mudfoot.doc.stu.mmu.ac.uk/students/abbasit/AndroidAssignment/addEmp.php";
public static final String URL_GET_ALL = "http://www.mudfoot.doc.stu.mmu.ac.uk/students/abbasit/AndroidAssignment//getAllEmp.php";
public static final String URL_GET_EMP = "http://mudfoot.doc.stu.mmu.ac.uk/students/abbasit/AndroidAssignment/getEmp.php?UserID=";
public static final String URL_UPDATE_EMP = "http://mudfoot.doc.stu.mmu.ac.uk/students/abbasit/AndroidAssignment/updateEmp.php";
public static final String URL_DELETE_EMP = "http://mudfoot.doc.stu.mmu.ac.uk/students/abbasit/AndroidAssignment/deleteEmp.php?UserID=";

//Keys that will be used to send the request to php scripts
public static final String KEY_EMP_ID = "UserID";
public static final String KEY_LAT = "Latitude";
public static final String KEY_LON = "Longitude";
public static final String KEY_TIMEINSERTED = "TimeInserted";

//JSON Tags
public static final String TAG_JSON_ARRAY="result";
public static final String TAG_ID = "UserID";
public static final String TAG_LAT = "Latitude";
public static final String TAG_LON = "Longitude";
public static final String TAG_TIMEINSERTED = "TimeInserted";

//employee id to pass with intent
public static final String EMP_ID = "UserID";
}

ViewAllEmployee.java

package com.example.assignment.assignment;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.ListView; 
import android.widget.SimpleAdapter;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class ViewAllEmployee extends Activity implements ListView.OnItemClickListener {

private ListView listView;

private String JSON_STRING;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_all_employee);
    listView = (ListView) findViewById(R.id.listView);
    listView.setOnItemClickListener(this);
    getJSON();
}


private void showEmployee() {
    JSONObject jsonObject = null;
    ArrayList<HashMap<String, String>> list = new ArrayList<HashMap<String,  String>>();
    try {
        jsonObject = new JSONObject(JSON_STRING);
        JSONArray result = jsonObject.getJSONArray(Config.TAG_JSON_ARRAY);

        for (int i = 0; i < result.length(); i++) {
            JSONObject jo = result.getJSONObject(i);
            String UserID = jo.getString(Config.TAG_ID);
            String Lat = jo.getString(Config.TAG_LAT);

            HashMap<String, String> employees = new HashMap<>();
            employees.put(Config.TAG_ID, UserID);
            employees.put(Config.TAG_LAT, Lat);
            list.add(employees);
        }

    } catch (JSONException e) {
        e.printStackTrace();
    }

    ListAdapter adapter = new SimpleAdapter(
            ViewAllEmployee.this, list, R.layout.list_item,
            new String[]{Config.TAG_ID, Config.TAG_LAT},
            new int[]{R.id.id, R.id.name});

    listView.setAdapter(adapter);
}

private void getJSON() {
    class GetJSON extends AsyncTask<Void, Void, String> {

        ProgressDialog loading;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            loading = ProgressDialog.show(ViewAllEmployee.this, "Fetching Data", "Wait...", false, false);
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            loading.dismiss();
            JSON_STRING = s;
            showEmployee();
        }

        @Override
        protected String doInBackground(Void... params) {
            RequestHandler rh = new RequestHandler();
            String s = rh.sendGetRequest(Config.URL_GET_ALL);
            return s;
        }
    }
    GetJSON gj = new GetJSON();
    gj.execute();
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    Intent intent = new Intent(this, ViewEmployee.class);
    HashMap<String, String> map = (HashMap)  parent.getItemAtPosition(position);
    String UserID = map.get(Config.TAG_ID).toString();
    intent.putExtra(Config.EMP_ID, UserID);
    startActivity(intent);
 }
 }

dbConnect.php

<?php

define('HOST','XXXX');
define('USER','XXXX');
define('PASS','XXXX');
define('DB','XXXX');

//Connecting to Database
$con = mysqli_connect(HOST,USER,PASS,DB) or die('Unable to Connect');

getAllEmp.php

<?php 
//Importing Database Script 
require_once('dbConnect.php');

//Creating sql query
$sql = "SELECT * FROM locationtrace";

//getting result 
$r = mysqli_query($con,$sql);

//creating a blank array 
$result = array();

//looping through all the records fetched
while($row = mysqli_fetch_array($r)){

    //Pushing name and id in the blank array created 
    array_push($result,array(
        "UserID"=>$row['UserID'],
        "Latitude"=>$row['Latitude']
        "Longitude"=>$row['Longitude']
        "TimeInserted"=>$row['TimeInserted']

    ));
}

//Displaying the array in json format 
echo json_encode(array('result'=>$result));

mysqli_close($con);