Making URL connections crashes my app

Question

I have an android Activity which crashes on making a HTTP GET request on the URL http://developernetwork.net78.net/readUnivs.php.

The app simply has to make an HTTP GET request to the server, which will return a list of educational universities as plain text separated by \n character. This list is then set as list data in a android.widget.Spinner with the help of android.widget.ArrayAdapter.

Here ia my PHP code on the server

<?php
    $conn = mysqli_connect($url, $username, $passwd, $database_name);

    $result = mysqli_query($conn, "SELECT University FROM Universities");

    while($row = mysqli_fetch_array())
        print($row["University"]."\n");

    print("END");

    mysqli_close($conn);
?>

And here is my android activity:

package com.adi.test;

import android.os.Bundle;
import android.app.Activity;
import android.widget.Spinner;
import android.widget.ArrayAdapter;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import java.util.ArrayList;
import java.util.Scanner;
import java.net.URL;
import java.net.HttpURLConnection;


public class TestActivity extends Activity {

    @Override
    public void onCreate(Bundle bundle) {

        super.onCreate(bundle);

        LinearLayout layout = new LinearLayout(this);
        layout.setOrientation(LinearLayout.VERTICAL);
        layout.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));

         try { 
                URL url = new URL("http://developernetwork.net78.net/readUnivs.php");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();

                conn.setRequestMethod("GET");
                conn.setRequestProperty("User-Agent", "Mozilla/5.0");
                Scanner sc = new Scanner(conn.getInputStream());

                ArrayList<String> list = new ArrayList<String>();
                while(sc.hasNextLine()) {

                    String line = sc.nextLine();
                    if(!line.equals("END"))
                        list.add(line);
                }
                sc.close();
            } catch(IOException exception) {

            }

            Spinner spinner = new Spinner(this);
            spinner.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
            ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, list);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

            spinner.setAdapter(adapter);
            layout.addView(spinner);
            setContentView(layout);
    }   
 }

The app compiles and installs fine on my LG L90. But it crashes as soon as it opens up. Why is this happening? If I add a simple loop that increments a number from 0 to 10 in place of my loop which reads the response of the server, the app runs fine. I think there is some issue with the loop. Can someone please point out what the issue could be?

check here : http://stackoverflow.com/questions/6343166/android-os-networkonmainthreadexception — RajaReddy PolamReddy, Nov 25 '14 at 10:52

score 1 · Answer 1 · answered Nov 25 '14 at 10:49

1

You are accessing the Url from main thread. So android.os.NetworkOnMainThreadException will be occured. It Will crash your application. Do your network operations on AsynTask.

answered Nov 25 '14 at 10:49

MathanG

1,195
10
22

Can you please give me an example code? Coz i also have to update the Spinner. That is, make changes in the UI. Which is I guess not allowed by threads apart from main thread in android. – Aditya Singh Nov 25 '14 at 10:51
http://programmerguru.com/android-tutorial/android-asynctask-example/ Refer this link. – MathanG Nov 25 '14 at 10:55

Carnal · Accepted Answer · 2014-11-25T10:55:20.830

1

Since Honeycomb (3.0) you cannot make a Network request in the UIThread. Consider using an AsyncTask and make the request in doInBackground.

Then make your changes in the UIThread in onPostExecute.

Here's an example: http://programmerguru.com/android-tutorial/android-asynctask-example/

edited Nov 25 '14 at 10:55

answered Nov 25 '14 at 10:50

Carnal

21,744
6
60
75

Can you please give me an example code? Coz i also have to update the Spinner. That is, make changes in the UI. Which is I guess not allowed by threads apart from main thread in android. – Aditya Singh Nov 25 '14 at 10:52
Check my edited answer. Going for lunch now, good luck! – Carnal Nov 25 '14 at 10:55

Making URL connections crashes my app

2 Answers2