试图获取 table 行计数值但得到错误转换结果 java.lang.NullPointerException: lock == null

Question

我是这方面的新手，所以我需要帮助解决我当前的问题，我正在尝试获取 table 行计数值，但 "Error parsing data org.json.JSONException: Value Result of type java.lang.String cannot be converted to JSONObject" 出现

这是我的 rowcount.php :

<?php

$mysqli = new mysqli("localhost", "root", "", "smkkimmanuel2");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

if ($result = $mysqli->query("SELECT * FROM pendaftaran")) {

    /* determine number of rows result set */
    $row_cnt = $result->num_rows;
 printf("Result set has %d rows.\n", $row_cnt);
 $response["rowcount"] = $row_cnt;
 die(json_encode($response));
}


?>

和我的 row_count_test class :

package id.wanda.smkkkristenimmanuelii;

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

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class Row_count_test extends Activity {

 private TextView testRowCount;
 
 // flag for Internet connection status
    Boolean isInternetPresent = false;
     
    // Connection detector class
    ConnectionDetector cd;

 // JSON parser class
 JSONParser jsonParser = new JSONParser();

 private static final String LOGIN_URL = "http://192.168.1.110/smkkimmanuel2/rowcount.php";


 // JSON element ids from repsonse of php script:
 private static final String TAG_ROWCOUNT = "rowcount";

 public static String row;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_row_count_test);
  
  testRowCount = (TextView) findViewById(R.id.test);
  new RowCount().execute();
 }
 public void rowCount(View v) {
  
  
 }

 class RowCount extends AsyncTask<String, String, String> {

  
  @Override
  protected String doInBackground(String... args) {
   String getRow;
   // getting product details by making HTTP request
   JSONObject json = jsonParser.makeHttpRequestRowCount(LOGIN_URL);
   try {
     getRow = json.getString(TAG_ROWCOUNT);
     row = getRow;
     
    
   } catch (JSONException e) {
    e.printStackTrace();
   }catch (NullPointerException e) {
       e.printStackTrace();
   }

   return row;
  }
  
  @Override
  protected void onPostExecute(String row) {
   // TODO Auto-generated method stub

   testRowCount.setText(row);
  }
 }

 
}

这是我的 JSONObject @PareshMayani 先生：

public JSONObject makeHttpRequestRowCount(String url, String method) {
 
        // Making HTTP request
        try {
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
 
                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
                
        } 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());
        }

        Log.d("JSON Parser", json);
        // 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;
 
    }

已编辑：问题似乎出现在 php 文件中，它返回空值。所以我需要有关 php 文件的帮助，

这是新的 logcat 错误：

05-26 11:28:46.530: E/Buffer Error(15945): Error converting result java.lang.NullPointerException: lock == null
05-26 11:28:46.530: E/JSON Parser(15945): Error parsing data org.json.JSONException: End of input at character 0 of

这是新的 rowcount.php 文件：

<?php

$mysqli = new mysqli("localhost", "root", "", "smkkimmanuel2");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

if ($result = $mysqli->query("SELECT * FROM pendaftaran")) {

    /* determine number of rows result set */
    $row_cnt = $result->num_rows;
 
 $response["rowcount"] = $row_cnt;
 echo json_encode($response);exit;
}


?>

Answer 1

删除 printf 行并替换如下

$row_cnt = $result->num_rows;

// remove this line
//printf("Result set has %d rows.\n", $row_cnt);

$response["rowcount"] = $row_cnt;

//replace this line
//die(json_encode($response));

echo json_encode($response);exit;

Answer 2

您面临 2 个问题：

1) 05-25 14:43:42.974: E/JSON Parser(23557): Error parsing data org.json.JSONException: Value Result of type java.lang.String cannot be converted to JSONObject

当您尝试从字符串创建 JSON 对象并且该字符串实际上不是 JSON 对象字符串时，会触发此异常。

如果您得到 {"rowcount":5} 那么这是正确的 JSON 对象。

2) java.lang.RuntimeException: An error occured while executing doInBackground() Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the > original thread that created a view hierarchy can touch its views.

问题描述本身是不言自明的。仅供参考，由于 doInBackground():

中写的下面一行，这个问题被提出

testRowCount.setText(row);

您不能在执行后台操作时更新任何视图（即 TextView 或任何其他视图）。换句话说，您可以仅从主线程更新 UI。

有两种方法：

在doInBackground()方法中实现runOnUiThread()，并在里面编写视图更新代码。
从 onPostExecute() 方法更新 UI。

Answer 3

我终于解决了我的问题，首先我创建了一个 config.php 用于连接到数据库

<?php

 $username = "root";
 $password = "";
 $host = "localhost";
 $dbname = "smkkimmanuel2";

    $options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'); 

    try 
    { 
        $db = new PDO("mysql:host={$host};dbname={$dbname};charset=utf8", $username, $password, $options); 
    } 
    catch(PDOException $ex) 
    { 
        die("Failed to connect to the database: " . $ex->getMessage()); 
    } 
     
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);      
    $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC); 
     
    if(function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()) 
    { 
        function undo_magic_quotes_gpc(&$array) 
        { 
            foreach($array as &$value) 
            { 
                if(is_array($value)) 
                { 
                    undo_magic_quotes_gpc($value); 
                } 
                else 
                { 
                    $value = stripslashes($value); 
                } 
            } 
        } 
     
        undo_magic_quotes_gpc($_POST); 
        undo_magic_quotes_gpc($_GET); 
        undo_magic_quotes_gpc($_COOKIE); 
    } 
     
    header('Content-Type: text/html; charset=utf-8'); 
     
    session_start(); 

?>

并将我的 rowcount.php 调整为如下所示：

<?php

//load and connect to MySQL database stuff
require("config.php");

    //gets user's info based off of a username.
    $query = "SELECT * FROM pendaftaran_calon_siswa";
    
    
    try {
        $stmt   = $db->prepare($query);
        $stmt->execute();
    }
    catch (PDOException $ex) {
        // For testing, you could use a die and message. 
        //die("Failed to run query: " . $ex->getMessage());
        
        //or just use this use this one to product JSON data:
        $response["success"] = 0;
        $response["message"] = "Database Error1. Please Try Again!";
        die(json_encode($response));
        
    }
    
    //fetching all the rows from the query
 $row = $stmt->fetchAll();
 $rows = count($row);
    
 $response["rowcount"] = $rows;
 echo json_encode($response);
    

?>

成功了，不知道怎么回事，谢谢大家的帮助，终于解决了这个问题。

试图获取 table 行计数值但得到错误转换结果 java.lang.NullPointerException: lock == null

trying to get table row count value but got Error converting result java.lang.NullPointerException: lock == null

javascript

php

android

json

jsonobject