安卓&PHP:使用PHP将数据从Android发布到mysql数据库

我需要将登录/注册数据从Android应用传递到localhost上的mysql数据库.我仍在学习过程中，上个星期对此有疑问.我读了数十页的问题和回答了Stack Overflow，并尝试了所有方法，但我无法解决此问题.您能在代码中指出我的问题吗，关于php和JSON我还是新手.

I need to pass login/register data from Android app to mysql database on localhost. I'm still in learning process, and have problem with this for last week. I read dozens of pages, questions & answers on Stack Overflow and tried everything but I just can't get this to work. Can You please point me the problem in my code, I'm still newbie regarding php and JSON.

Android，活动和应用程序；AsyncTask类:

Android, Activity & AsyncTask Class:

package com.example.mario.datadrivenassignmenttwo;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;

public class DbManager extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.register);
}

public void register(View v) {
    EditText uname = (EditText) findViewById(R.id.username);
    EditText pw = (EditText) findViewById(R.id.password);

    String username = uname.getText().toString();
    System.out.println("username is: " + username);
    String password = pw.getText().toString();
    System.out.println("password is: " + password);

    Uploader task = new Uploader();
    task.execute(new String[] { "http://10.0.2.2/user_db/senddata.php", username, password });
}

public class Uploader extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {

        /* 
        String response = "Finished";
        try {
            postHttpContent(params[0],params[1],params[2]);
        } catch (IOException e) {
            Log.e("error", e.toString());
        }
        return response;
        */

        try {
            String urlParam = params[0];
            String username = params[1];
            String password = params[2];
            String charset = java.nio.charset.StandardCharsets.UTF_8.name();

            String query = String.format("username=%s&password=%s", URLEncoder.encode(username, charset), URLEncoder.encode(password, charset));

            /*
            URLConnection conn = new URL(urlParam).openConnection();
            conn.setDoOutput(true);
            conn.setRequestProperty("Accept-Charset", charset);
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=" + charset);

            OutputStream output = conn.getOutputStream();
            output.write(query.getBytes(charset));
            output.flush();
            output.close();
            */

            URL url = new URL(urlParam);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
            writer.write(query);
            writer.close();
            if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {

                System.out.println("It's ok!");
                System.out.println(query);

            } else {

                System.out.println("Error code there");

            }

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

        return "Finished";
    }

    @Override
    protected void onPostExecute(String result) {
        Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show();
    }

}
}

还有我的PHP:

<?php
// connect to database
$hostname = "localhost";
$username = "root";
$password = "root";
$dbname = "user_db";


$link = new mysqli($hostname, $username, $password, $dbname);

// get the JSONArray the app sends
$contents = file_get_contents('php://input');

$jsonArray = json_decode($contents, true);
$jsonCount = count($jsonArray);

for ($i = 0; $i < $jsonCount; $i++) {
$item = $jsonArray[$i];
$itemUsername = utf8_decode($item['username']);
$itemPassword = utf8_decode($item['password']);
// parse the other json attributes here like the one above

$sql = "INSERT INTO users (username, password) VALUES ('$itemUsername', '$itemPassword')";

if ($link->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $link->error;
}
}

$link->close();
?>

有很多注释的代码，这是我尝试过的所有内容，还有一些其他代码，但无济于事.我还尝试将所有连接和其余连接放到一个方法中，并在AsyncTask类中调用该方法，但同样失败.由于我不了解PHP，因此不确定问题是否出在我的Android代码或PHP文件中.

There is a lot of commented code, that's all I have tried, and some other code as well, but nothing works. I also tried putting all the connection and rest into one method and calling that method inside AsyncTask class, that failed aswell. Since I don't know PHP, I'm not sure if the problem is in my Android code or PHP file.

非常感谢.