java - Android Http POST request doesen't work

I have this Android code :

package com.example.webtestconnection;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;

import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    private Button login;
    private EditText username, password;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        login = (Button) findViewById(R.id.ok);
        username = (EditText) findViewById(R.id.name);
        password = (EditText) findViewById(R.id.password);

        login.setOnClickListener(new OnClickListener() {


            @Override
            public void onClick(View v) {

                String   mUsername = username.getText().toString();
                String  mPassword = password.getText().toString();

                tryLogin(mUsername, mPassword);
            }
        });

    }

    protected void tryLogin(String mUsername, String mPassword)
    {
        HttpURLConnection connection;
        OutputStreamWriter request = null;

        URL url = null;
        String response = null;
        String parameters = "username="+mUsername+"&password="+mPassword;


        try
        {
            url = new URL("http://welovelamacompany.altervista.org/test2.php");
            connection = (HttpURLConnection) url.openConnection();
            connection.setDoOutput(true);
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setRequestMethod("POST");

            request = new OutputStreamWriter(connection.getOutputStream());

            request.write(parameters);
            request.flush();
            request.close();
            String line = "";
            InputStreamReader isr = new InputStreamReader(connection.getInputStream());
            BufferedReader reader = new BufferedReader(isr);
            StringBuilder sb = new StringBuilder();
            while ((line = reader.readLine()) != null)
            {
                sb.append(line + "\n");

            }
            // Response from server after login process will be stored in response variable.
            response = sb.toString();
            // You can perform UI operations here
            Toast.makeText(this,"Message from Server: \n"+ response, Toast.LENGTH_LONG).show();
            isr.close();
            reader.close();

        }
        catch(IOException e)

        {
            // Error
        }
    }
}

And this is the php page code:

//impostazioni server phpmyadmin per poter accedere al db
    $servername = "servername";
    $username = "username";
    $password = "password";
    $databasename = "my_databasename";
    $Nome_Giocatore = $_POST['username'];
    $PasswordGiocatore = $_POST['password'];
    try {
        $conn = new PDO("mysql:host=$servername;dbname=$databasename", $username, $password);
        //imposto una modalità di eccezzione errore

        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        //stampo che la connessione è riuscita
        $sql=$conn->query("SELECT Password_Giocatore FROM Giocatori WHERE Nome_Giocatore=\"$Nome_Giocatore\"");
        $control = $sql->fetch();
        $controllo=$control['Password_Giocatore'];
        if (password_verify($PasswordGiocatore, $controllo)){
            echo "Success";
        } else {
            echo "Error";
        }

        $conn->exec($sql);
    } catch(PDOException $e){
                    //stampo che la connessione è fallita e l'errore che ha causato il fallimento
                    echo "Qualcosa è andato storto :(. Errore: 
".$e->getMessage();
                }
    $conn = null;
?>

But when I run it it give me this error:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.webtestconnection, PID: 23550
android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1166)
at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
at java.net.InetAddress.getAllByName(InetAddress.java:214)
at com.android.okhttp.internal.Dns$1.getAllByName(Dns.java:28)

at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:216)
at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:122)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:390)
at com.android.okhttp.internal.http.HttpEngine.sendSocketRequest(HttpEngine.java:343)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:289)
at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:345)
at com.android.okhttp.internal.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:89)
at com.android.okhttp.internal.http.HttpURLConnectionImpl.getOutputStream(HttpURLConnectionImpl.java:197)
at com.example.webtestconnection.MainActivity.tryLogin(MainActivity.java:62)
at com.example.webtestconnection.MainActivity$1.onClick(MainActivity.java:40)

at android.view.View.performClick(View.java:4633)
at android.view.View$PerformClick.run(View.java:19270)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5476)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)

at dalvik.system.NativeStart.main(Native Method)

Why? How can I fix it? Thanks for help

P.S. I have the internet permission in the manifest

Answer

Please use AsyncTask to make an API call, you are getting exception because you are calling it on MainThread.

class LoginTask extends AsyncTask {


    private Exception exception;

    protected YourResponse doInBackground(String... urls) {
        try {
             URL url = new URL(urls[0]);
            //your login code
        } catch (Exception e) {
            this.exception = e;
        } 

    }
    protected void onPostExecute(YourResponse response) {
        // TODO: check this.exception
        // TODO: do something with the feed
    }
}

and add this line in your code

new LoginTask().execute(url);

EDITED
You can below libraries for Network calls, easier and optimized for Network calls

1. Retrofit


2. Volley