Android.Os.Networkonmainthreadexception with Android 4.2

android.os.NetworkOnMainThreadException with android 4.2

Write below code into your MainActivity file after setContentView(R.layout.activity_main);

if (android.os.Build.VERSION.SDK_INT > 9) {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
}

And below import statement into your java file.

import android.os.StrictMode;

How can I fix 'android.os.NetworkOnMainThreadException'?

NOTE : AsyncTask was deprecated in API level 30.

AsyncTask | Android Developers

This exception is thrown when an application attempts to perform a networking operation on its main thread. Run your code in AsyncTask:

class RetrieveFeedTask extends AsyncTask<String, Void, RSSFeed> {

    private Exception exception;

    protected RSSFeed doInBackground(String... urls) {
        try {
            URL url = new URL(urls[0]);
            SAXParserFactory factory = SAXParserFactory.newInstance();
            SAXParser parser = factory.newSAXParser();
            XMLReader xmlreader = parser.getXMLReader();
            RssHandler theRSSHandler = new RssHandler();
            xmlreader.setContentHandler(theRSSHandler);
            InputSource is = new InputSource(url.openStream());
            xmlreader.parse(is);

            return theRSSHandler.getFeed();
        } catch (Exception e) {
            this.exception = e;

            return null;
        } finally {
            is.close();
        }
    }

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

How to execute the task:

In MainActivity.java file you can add this line within your oncreate() method

new RetrieveFeedTask().execute(urlToRssFeed);

Don't forget to add this to AndroidManifest.xml file:

<uses-permission android:name="android.permission.INTERNET"/>

NetworkOnMainThreadException on Runnable

Runnable is a simple interface, that, as per the Java documentation, "should be implemented by any class whose instances are intended to be executed by a thread." (Emphasis mine.)

For instance, defining a Runnable as follows will simply execute it in the same thread as it's created:

new Runnable() {
    @Override
    public void run() {
        Log.d("Runnable", "Hello, world!");
    }
}.run();

Observe that all you're actually doing here is creating a class and executing its public method run(). There's no magic here that makes it run in a separate thread. Of course there isn't; Runnable is just an interface of three lines of code!

Compare this to implementing a Thread (which implements Runnable):

new Thread() {
    @Override
    public void run() {
        Log.d("Runnable", "Hello, world!");
    }
}.start();

The primary difference here is that Thread's start() method takes care of the logic for spawning a new thread and executing the Runnable's run() inside it.

Android's AsyncTask further facilitates thread execution and callbacks onto the main thread, but the concept is the same.

Error networkonmainthreadexception null

You need to move the part of the network connection to a separate thread, better using AsyncTask..

ex:

 private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
 protected Long doInBackground(URL... urls) {
     int count = urls.length;
     long totalSize = 0;
     for (int i = 0; i < count; i++) {
         totalSize += Downloader.downloadFile(urls[i]);
         publishProgress((int) ((i / (float) count) * 100));
         // Escape early if cancel() is called
         if (isCancelled()) break;
     }
     return totalSize;
 }

 protected void onProgressUpdate(Integer... progress) {
     setProgressPercent(progress[0]);
 }

 protected void onPostExecute(Long result) {
     showDialog("Downloaded " + result + " bytes");
 }

}

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