android - 转换结果时出错 java.lang.NullPointerException : lock == null

Question

我刚开始开发 android 应用程序。我已经阅读了很多关于我提出的问题的相关帖子，但是帖子中的提示或解决方案并没有解决我的问题。 (已经寻找解决方案一周了，真的需要帮助才能继续我的项目)非常感谢...

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import com.example.aroma.slidingmenu.listener.JSONParser;
import android.app.ListFragment;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class ResultListFragment extends ListFragment {
    
    TextView resultView;

    
public ResultListFragment(){}
    
    //progress dialog
    private ProgressDialog pDialog;
    
    //creating JSON Parser object
    JSONParser jParser = new JSONParser();
    
    ArrayList<HashMap<String,String>> customerList;
    
    //url to get the customer list
    private static String url_search="http://192.168.1.3:80/test/getAllCustomers.php";
    
    //JSON Node names
    private static final String TAG_SUCCESS="success";
    private static final String TAG_CUSTOMER="customers";
    private static final String TAG_FNAME="FirstName";
    private static final String TAG_LNAME="LastName";
    private static final String TAG_AGE="Age";
    private static final String TAG_MOBILE="Mobile";
    
    //product JSONArray
    JSONArray customers=null;
    //search key value
    public String searchKey;
    
    
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
    
        View rootView = inflater.inflate(R.layout.activity_searchresult_list, container, false);
            
        Toast.makeText(getActivity(),"Search result in listview",Toast.LENGTH_LONG).show();
        
        Intent intent = getActivity().getIntent();
        searchKey = intent.getStringExtra("message");
        //Toast.makeText(getActivity(), searchKey, Toast.LENGTH_LONG).show();
        
        //hshmap for listview
        customerList= new ArrayList<HashMap<String,String>>();
        
        
        //Loading customer in background thread
        new LoadCustomer().execute();

        return rootView;       
    }
    
    @Override 
        public void onViewCreated (View view, Bundle savedInstanceState) {
            
        ListView lv =getListView();
        
        lv.setOnItemSelectedListener(new OnItemSelectedListener(){

            @Override
            public void onItemSelected(AdapterView<?> parent, View view,
                    int position, long id) {
                // TODO Auto-generated method stub
                String iid=((TextView)view.findViewById(R.id.FirstName)).getText().toString();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
                // TODO Auto-generated method stub
                
            }
        });
    }
    
    /**
        * Background Async Task to load customers by making HTTP request
        * */
    class LoadCustomer extends AsyncTask<String, String, String>{
        /**
            * Before starting background thread show progress dialog
            * */
        @Override
        protected void onPreExecute(){
            super.onPreExecute();
            pDialog=new ProgressDialog(getActivity());  //pDialog=new ProgressDialog(ResultListFragment.this);
            pDialog.setMessage("Loading customers. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }
        
        /**
            * getting customers url
            * **/
        protected String doInBackground(String... args){
            //Building Parameters
            List<NameValuePair> params= new ArrayList<NameValuePair>();
            //value captured from previous intent
            params.add(new BasicNameValuePair("FirstName", searchKey));
            //getting JSON string from url
            JSONObject json = jParser.makeHttpRequest(url_search, "GET", params);
            //check your log cat for JSON response
            Log.d("Search customer", json.toString());
            
            try{
                //checking for SUCCESS TAG
                int success=json.getInt(TAG_SUCCESS);
                
                if(success==1){
                    //product found
                    //Getting array of products
                    customers=json.getJSONArray(TAG_CUSTOMER);
                    
                    //looping through all products
                    for(int i=0;i<customers.length();i++){
                        JSONObject c=customers.getJSONObject(i);
                        
                        //storing each json item in variable
                        String fname=c.getString(TAG_FNAME);
                        String lname=c.getString(TAG_LNAME);
                        String age=c.getString(TAG_AGE);
                        String mobile=c.getString(TAG_MOBILE);
                        
                        //creating new HashMap
                        HashMap<String, String> map=new HashMap<String, String>();
                        
                        //adding each child node to HashMap key =>value
                        map.put(TAG_FNAME, fname);
                        map.put(TAG_LNAME, lname);
                        map.put(TAG_AGE, age);
                        map.put(TAG_MOBILE, mobile);
                        
                        //adding HashList to ArrayList
                        customerList.add(map);
                    }
                }else{
                        //no customer found
                        //do sth
                    Handler handler =  new Handler(getActivity().getMainLooper());
                    handler.post( new Runnable(){
                        public void run(){
                            Toast.makeText(getActivity(),"no customer found" ,Toast.LENGTH_LONG).show(); 
                        }
                    });
                    }
                }catch (JSONException e){
                    e.printStackTrace();
                }
                
                //return "success";
                return null;
            }
        
        /**
            * After completing background task dismiss the progress dialog
            * **/
        protected void onPostExecute(String file_url){
            //dimiss the dialog after getting the related customer
            pDialog.dismiss();
            getActivity().runOnUiThread(new Runnable(){
                public void run(){
                    /**
                        * updating parsed JSON data into ListView
                        * **/
                    ListAdapter adapter =new SimpleAdapter(
                            getActivity(), customerList, 
                            R.layout.list_item, new String[]{ TAG_FNAME, TAG_LNAME, TAG_AGE, TAG_MOBILE},
                            new int[]{R.id.FirstName,R.id.LastName,R.id.Age,R.id.Mobile});
                        //updating listview
                        setListAdapter(adapter);
                }
            });

        }

    }
    
    
}

JSONParser.java

package com.example.aroma.slidingmenu.listener;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;http://stackoverflow.com/editing-help

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {

        // Making HTTP request
        try {
            
            // check for request method
            if(method.equals("POST")){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
                
            }else if(method.equals("GET")){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                //is = httpEntity.getContent();
                
                String all=EntityUtils.toString(httpEntity);
                    Log.d("response",all);
            }           
            

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }       
}

getAllCustomers.php

$response = array();
$con = mysql_connect("localhost","root","");
if (!$con)
    {
    die('Could not connect: ' . mysql_error());
    }
mysql_select_db("testdatabase", $con);

$FirstName=$_GET["FirstName"];
$result = mysql_query("SELECT * FROM customer where FirstName like '%$FirstName%' ");


if(mysql_num_rows($result)>0){
    // looping through all results
    // products node
    $response["customers"] = array();
    
    while ($row = mysql_fetch_array($result)) {
        // temp user array
        $customers = array();
        $customers["FirstName"] = $row["FirstName"];
        $customers["LastName"] = $row["LastName"];
        $customers["Age"] = $row["Age"];
        $customers["Mobile"] = $row["Mobile"];
    
        // push single product into final response array
        array_push($response["customers"], $customers);
}
// success
    $response["success"] = 1;
        // echoing JSON response
    echo json_encode($response);
} else {
    // no products found
    $response["success"] = 0;
    $response["message"] = "No products found";
    
    // echo no users JSON
    echo json_encode($response);
}

我从 Logcat 保存的错误:

02-12 17:17:50.599: E/Buffer Error(13636): Error converting result java.lang.NullPointerException: lock == null02-12 17:17:50.599: E/JSON Parser(13636): Error parsing data org.json.JSONException: End of input at character 0 of 02-12 17:17:50.604: E/AndroidRuntime(13636): FATAL EXCEPTION: AsyncTask #402-12 17:17:50.604: E/AndroidRuntime(13636): java.lang.RuntimeException: An error occured while executing doInBackground()02-12 17:17:50.604: E/AndroidRuntime(13636):    at android.os.AsyncTask$3.done(AsyncTask.java:299)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.FutureTask.setException(FutureTask.java:219)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.FutureTask.run(FutureTask.java:239)02-12 17:17:50.604: E/AndroidRuntime(13636):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.lang.Thread.run(Thread.java:838)02-12 17:17:50.604: E/AndroidRuntime(13636): Caused by: java.lang.NullPointerException02-12 17:17:50.604: E/AndroidRuntime(13636):    at com.example.aroma.slidingmenu.ResultListFragment$LoadCustomer.doInBackground(ResultListFragment.java:136)02-12 17:17:50.604: E/AndroidRuntime(13636):    at com.example.aroma.slidingmenu.ResultListFragment$LoadCustomer.doInBackground(ResultListFragment.java:1)02-12 17:17:50.604: E/AndroidRuntime(13636):    at android.os.AsyncTask$2.call(AsyncTask.java:287)02-12 17:17:50.604: E/AndroidRuntime(13636):    at java.util.concurrent.FutureTask.run(FutureTask.java:234)02-12 17:17:50.604: E/AndroidRuntime(13636):    ... 4 more

Answer 1

尝试在onActivityCreated中调用asynctask

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.activity_searchresult_list, container, false);         

    return rootView;       
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    Toast.makeText(getActivity(),"Search result in listview",Toast.LENGTH_LONG).show();

    Intent intent = getActivity().getIntent();
    searchKey = intent.getStringExtra("message");
    //Toast.makeText(getActivity(), searchKey, Toast.LENGTH_LONG).show();

    //hshmap for listview
    customerList= new ArrayList>();


    //Loading customer in background thread
    new LoadCustomer().execute();

}