Monday, 29 June 2015

android.os.NetworkOnMainThreadException android doing time consuming things in a new thread AsyncTask, IntentService



To solve it you can:


StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();

StrictMode.setThreadPolicy(policy); 

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

But it is not a good idea to do so. because you don't want the network loading block you app.



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;
        }
    }

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

new RetrieveFeedTask().execute(urlToRssFeed);

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

IntentService



Step 1: Create an IntentService to perform the download. You can tell it what to download via Intent extra's, and pass it a PendingIntent to use to return the result to the Activity:
import android.app.IntentService;
import android.app.PendingIntent;
import android.content.Intent;
import android.util.Log;

import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

public class DownloadIntentService extends IntentService {

    private static final String TAG = DownloadIntentService.class.getSimpleName();

    public static final String PENDING_RESULT_EXTRA = "pending_result";
    public static final String URL_EXTRA = "url";
    public static final String RSS_RESULT_EXTRA = "url";

    public static final int RESULT_CODE = 0;
    public static final int INVALID_URL_CODE = 1;
    public static final int ERROR_CODE = 2;

    private IllustrativeRSSParser parser;

    public DownloadIntentService() {
        super(TAG);

        // make one and re-use, in the case where more than one intent is queued
        parser = new IllustrativeRSSParser();
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        PendingIntent reply = intent.getParcelableExtra(PENDING_RESULT_EXTRA);
        InputStream in = null;
        try {
            try {
                URL url = new URL(intent.getStringExtra(URL_EXTRA));
                IllustrativeRSS rss = parser.parse(in = url.openStream());

                Intent result = new Intent();
                result.putExtra(RSS_RESULT_EXTRA, rss);

                reply.send(this, RESULT_CODE, result);
            } catch (MalformedURLException exc) {
                reply.send(INVALID_URL_CODE);
            } catch (Exception exc) {
                // could do better by treating the different sax/xml exceptions individually
                reply.send(ERROR_CODE);
            }
        } catch (PendingIntent.CanceledException exc) {
            Log.i(TAG, "reply cancelled", exc);
        }
    }
}
Step 2: Register the service in the manifest:
<service
        android:name=".DownloadIntentService"
        android:exported="false"/>
Step 3: Invoke the service from the Activity, passing a PendingResult object which the Service will use to return the result:
PendingIntent pendingResult = createPendingResult(
    RSS_DOWNLOAD_REQUEST_CODE, new Intent(), 0);
Intent intent = new Intent(getApplicationContext(), DownloadIntentService.class);
intent.putExtra(DownloadIntentService.URL_EXTRA, URL);
intent.putExtra(DownloadIntentService.PENDING_RESULT_EXTRA, pendingResult);
startService(intent);
Step 4: Handle the result in onActivityResult:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == RSS_DOWNLOAD_REQUEST_CODE) {
        switch (resultCode) {
            case DownloadIntentService.INVALID_URL_CODE:
                handleInvalidURL();
                break;
            case DownloadIntentService.ERROR_CODE:
                handleError(data);
                break;
            case DownloadIntentService.RESULT_CODE:
                handleRSS(data);
                break;
        }
        handleRSS(data);
    }
    super.onActivityResult(requestCode, resultCode, data);
}
A github project containing a complete working Android-Studio/gradle project is available here.


http://stackoverflow.com/questions/6343166/android-os-networkonmainthreadexception







In the ArrayAdapter:

http://lucasr.org/2012/04/05/performance-tips-for-androids-listview/






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