php - 登录导致 Android 应用程序崩溃

Question

我已经按照此链接制作了一个允许用户使用数据库登录的应用程序 http://www.mybringback.com/tutorial-series/13239/android-mysql-php-json-part-6-json-parsing-and-android-design/

但是登录后就崩溃了。我已经搜索了几个小时并阅读了一些具有相同问题的问题，但没有一个解决方案对我有用。

我正在尝试在 Android 模拟器中运行它。

登录.java

    package com.example.mysqltest;

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

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

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Login extends Activity implements OnClickListener {

    private EditText user, pass;
    private Button mSubmit, mRegister;

    // Progress Dialog
    private ProgressDialog pDialog;

    // JSON parser class


    // php login script location:

    // localhost :
    // testing on your device
    // put your local ip instead, on windows, run CMD > ipconfig
    // or in mac's terminal type ifconfig and look for the ip under en0 or en1
    // private static final String LOGIN_URL =
    // "http://xxx.xxx.x.x:1234/webservice/login.php";

    // testing on Emulator:



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        // setup input fields
        user = (EditText) findViewById(R.id.username);
        pass = (EditText) findViewById(R.id.password);

        // setup buttons
        mSubmit = (Button) findViewById(R.id.login);
        mRegister = (Button) findViewById(R.id.register);

        // register listeners
        mSubmit.setOnClickListener(this);
        mRegister.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
        case R.id.login:
            new AttemptLogin().execute();
            break;
        case R.id.register:
            Intent i = new Intent(this, Register.class);
            startActivity(i);
            break;

        default:
            break;
        }
    }

    class AttemptLogin extends AsyncTask<String, String, String> {
        private static final String LOGIN_URL = "http://127.0.0.1:1234/webservice/login.php";

        // testing from a real server:
        // private static final String LOGIN_URL =
        // "http://www.mybringback.com/webservice/login.php";

        // JSON element ids from repsonse of php script:
        private static final String TAG_SUCCESS = "success";
        private static final String TAG_MESSAGE = "message";
        boolean failure = false;
        String username, password;
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
             username = user.getText().toString();
                password = pass.getText().toString();
            pDialog = new ProgressDialog(Login.this);
            pDialog.setMessage("Attempting login...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        @Override
        protected String doInBackground(String... args) {
            // TODO Auto-generated method stub
            // Check for success tag
            int success;
            JSONParser jsonParser = new JSONParser();
            String username = user.getText().toString();
            String password = pass.getText().toString();
            try {
                // Building Parameters
                List<NameValuePair> params = new ArrayList<NameValuePair>();
                params.add(new BasicNameValuePair("username", username));
                params.add(new BasicNameValuePair("password", password));

                Log.d("request!", "starting");
                // getting product details by making HTTP request
                JSONObject json = jsonParser.makeHttpRequest(LOGIN_URL, "POST",
                        params);

                // check your log for json response
                Log.d("Login attempt", json.toString());

                // json success tag
                success = json.getInt(TAG_SUCCESS);
                if (success == 1) {
                    Log.d("Login Successful!", json.toString());
                    // save user data
                    SharedPreferences sp = PreferenceManager
                            .getDefaultSharedPreferences(Login.this);
                    Editor edit = sp.edit();
                    edit.putString("username", username);
                    edit.commit();

                    Intent i = new Intent(Login.this, ReadComments.class);
                    finish();
                    startActivity(i);
                    return json.getString(TAG_MESSAGE);
                } else {
                    Log.d("Login Failure!", json.getString(TAG_MESSAGE));
                    return json.getString(TAG_MESSAGE);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;

        }

        protected void onPostExecute(String file_url) {
            // dismiss the dialog once product deleted
            pDialog.dismiss();
            if (file_url != null) {
                Toast.makeText(Login.this, file_url, Toast.LENGTH_LONG).show();
            }

        }

    }

}

Config.inc.php

<?php 

    // These variables define the connection information for your MySQL database 
    // This is also for the Xampp example,  if you are hosting on your own server,
    //make the necessary changes (mybringback_travis, etc.)


$username = "root"; 
$password = ""; 
$host = "127.0.0.1"; 
$dbname = "webservice"; 

    // UTF-8 is a character encoding scheme that allows you to conveniently store 
    // a wide varienty of special characters, like ¢ or €, in your database. 
    // By passing the following $options array to the database connection code we 
    // are telling the MySQL server that we want to communicate with it using UTF-8 
    // See Wikipedia for more information on UTF-8: 
    // http://en.wikipedia.org/wiki/UTF-8 
    $options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'); 

    // A try/catch statement is a common method of error handling in object oriented code. 
    // First, PHP executes the code within the try block.  If at any time it encounters an 
    // error while executing that code, it stops immediately and jumps down to the 
    // catch block.  For more detailed information on exceptions and try/catch blocks: 
    // http://us2.php.net/manual/en/language.exceptions.php 
    try 
    { 
        // This statement opens a connection to your database using the PDO library 
        // PDO is designed to provide a flexible interface between PHP and many 
        // different types of database servers.  For more information on PDO: 
        // http://us2.php.net/manual/en/class.pdo.php 
        $db = new PDO("mysql:host={$host};dbname={$dbname};charset=utf8", $username, $password, $options); 
    } 
    catch(PDOException $ex) 
    { 
        // If an error occurs while opening a connection to your database, it will 
        // be trapped here.  The script will output an error and stop executing. 
        // Note: On a production website, you should not output $ex->getMessage(). 
        // It may provide an attacker with helpful information about your code 
        // (like your database username and password). 
        die("Failed to connect to the database: " . $ex->getMessage()); 
    } 

    // This statement configures PDO to throw an exception when it encounters 
    // an error.  This allows us to use try/catch blocks to trap database errors. 
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 

    // This statement configures PDO to return database rows from your database using an associative 
    // array.  This means the array will have string indexes, where the string value 
    // represents the name of the column in your database. 
    $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC); 

    // This block of code is used to undo magic quotes.  Magic quotes are a terrible 
    // feature that was removed from PHP as of PHP 5.4.  However, older installations 
    // of PHP may still have magic quotes enabled and this code is necessary to 
    // prevent them from causing problems.  For more information on magic quotes: 
    // http://php.net/manual/en/security.magicquotes.php 
    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); 
    } 

    // This tells the web browser that your content is encoded using UTF-8 
    // and that it should submit content back to you using UTF-8 
    header('Content-Type: text/html; charset=utf-8'); 

    // This initializes a session.  Sessions are used to store information about 
    // a visitor from one web page visit to the next.  Unlike a cookie, the information is 
    // stored on the server-side and cannot be modified by the visitor.  However, 
    // note that in most cases sessions do still use cookies and require the visitor 
    // to have cookies enabled.  For more information about sessions: 
    // http://us.php.net/manual/en/book.session.php 
    session_start(); 

    // Note that it is a good practice to NOT end your PHP files with a closing PHP tag. 
    // This prevents trailing newlines on the file from being included in your output, 
    // which can cause problems with redirecting users.



?>

登录.php

<?php

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

if (!empty($_POST)) {
    //gets user's info based off of a username.
    $query = " 
            SELECT 
                id, 
                username, 
                password
            FROM users 
            WHERE 
                username = :username 
        ";

    $query_params = array(
        ':username' => $_POST['username']
    );

    try {
        $stmt   = $db->prepare($query);
        $result = $stmt->execute($query_params);
    }
    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));

    }

    //This will be the variable to determine whether or not the user's information is correct.
    //we initialize it as false.
    $validated_info = false;

    //fetching all the rows from the query
    $row = $stmt->fetch();
    if ($row) {
        //if we encrypted the password, we would unencrypt it here, but in our case we just
        //compare the two passwords
        if ($_POST['password'] === $row['password']) {
            $login_ok = true;
        }
    }

    // If the user logged in successfully, then we send them to the private members-only page 
    // Otherwise, we display a login failed message and show the login form again 
    if ($login_ok) {
        $response["success"] = 1;
        $response["message"] = "Login successful!";
        die(json_encode($response));
    } else {
        $response["success"] = 0;
        $response["message"] = "Invalid Credentials!";
        die(json_encode($response));
    }
} else {
?>
        <h1>Login</h1> 
        <form action="login.php" method="post"> 
            Username:<br /> 
            <input type="text" name="username" placeholder="username" /> 
            <br /><br /> 
            Password:<br /> 
            <input type="password" name="password" placeholder="password" value="" /> 
            <br /><br /> 
            <input type="submit" value="Login" /> 
        </form> 
        <a href="register.php">Register</a>
    <?php
}

?> 

Logcat 报告

 09-20 11:02:38.196: E/AndroidRuntime(913): FATAL EXCEPTION: AsyncTask #1
09-20 11:02:38.196: E/AndroidRuntime(913): Process: com.example.mysqltest, PID: 913
09-20 11:02:38.196: E/AndroidRuntime(913): java.lang.RuntimeException: An error occured while executing doInBackground()
09-20 11:02:38.196: E/AndroidRuntime(913):  at android.os.AsyncTask$3.done(AsyncTask.java:300)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.FutureTask.run(FutureTask.java:242)
09-20 11:02:38.196: E/AndroidRuntime(913):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.lang.Thread.run(Thread.java:841)
09-20 11:02:38.196: E/AndroidRuntime(913): Caused by: java.lang.NullPointerException
09-20 11:02:38.196: E/AndroidRuntime(913):  at com.example.mysqltest.Login$AttemptLogin.doInBackground(Login.java:131)
09-20 11:02:38.196: E/AndroidRuntime(913):  at com.example.mysqltest.Login$AttemptLogin.doInBackground(Login.java:1)
09-20 11:02:38.196: E/AndroidRuntime(913):  at android.os.AsyncTask$2.call(AsyncTask.java:288)
09-20 11:02:38.196: E/AndroidRuntime(913):  at java.util.concurrent.FutureTask.run(FutureTask.java:237)
09-20 11:02:38.196: E/AndroidRuntime(913):  ... 4 more

Answer 1

JSONParser 是您用于获取和解析的自定义类吗？

无论如何，如果我们的自定义类方法出现异常，响应可能为 null，对吧？但是你没有检查对象是否为空。不直接检查打印值 json.tostring();如果你的 json 为 null，那么它只会抛出 nullpointerException。尝试更改下面的代码并检查一次。

替换代码

JSONObject json = jsonParser.makeHttpRequest(LOGIN_URL, "POST",
                        params);

至

DefaultHttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
HttpResponse httpresponse = httpclient.execute(httppost);
HttpEntity httpentity = httpresponse.getEntity();
JSONObject json = null;
if(TextUtils.isEmpty(EntityUtils.toString(httpentity))) {
   Log.d("Login attempt", "Json is empty or null");
} else {
   json = new JSONObject(EntityUtils.toString(httpentity));
}