Android AsyncTask Activity Crash RSS Reader

Question

I'm trying to build an RSS reader and put the rss feed fetch as ansyctask, that returns a feed in list view, or returns a text view saying "no internet connection" but the app still crashes, I don't know what's wrong, can you help please.

here is the code:

package rss;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.TextView;

import com.enporan.polytechoran.R;

public class RSSActivity extends ActionBarActivity {
    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_news);


           rssfeedget alpha = new rssfeedget();
          alpha.execute();



    }

    private class rssfeedget extends AsyncTask<String, Void, FeedSource> {


        protected void onPreExecute() {

        }

        @Override
        protected FeedSource doInBackground(String... params) {
            FeedSource f = new HttpFeedSource();
            if(f!=null)
                return f;
            else {
               return null;
            }
        }

        @Override
        protected void onPostExecute(FeedSource result){
            ListView rssItemList = (ListView) findViewById(R.id.rssListview);
            rssItemList.setVerticalFadingEdgeEnabled(true);
            if(doInBackground()==null){
                TextView tv= (TextView) findViewById(R.id.textView2);
                tv.setText("No internet Connection...");

            }
            else{

                RSSItemAdapter adapter = new RSSItemAdapter(getApplicationContext(), R.layout.rssitem, doInBackground().getFeed());
                rssItemList.setAdapter(adapter);
            }

        }
    }




    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_news, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

}

Answer 1

Here is the code:

private class rssfeedget extends AsyncTask<String, Void, List<RSSItem>> {
    private List<RSSItem> result;

    protected void onPreExecute() {

    }

    @Override
    protected List<RSSItem> doInBackground(String... params) {
        FeedSource f = new HttpFeedSource();
        if(f.getFeed()==null)
            return null;
        else {
            this.result = f.getFeed(); // Execute getFeed in doInBackground
            return result;
        }
    }

    @Override
    protected void onPostExecute(List<RSSItem> result){


        if(doInBackground()==null){
            TextView tv= (TextView) findViewById(R.id.textView2);
            tv.setText("No internet Connection...");

        }
        else{
            ListView rssItemList = (ListView) findViewById(R.id.rssListview);
            rssItemList.setVerticalFadingEdgeEnabled(true);
            RSSItemAdapter adapter = new RSSItemAdapter(getApplicationContext(), R.layout.rssitem, this.result);
            rssItemList.setAdapter(adapter);
        }

    }
}

Answer 2

As @coelho pointed out, the FeedSource.getFeed() shouldn't be executed in the UI thread. You must now that the onPreExecute and onPostExecute methods are executed inside the UI thread, while the doInBackground method isn't.

Here's what you can do: in your AsyncTask class, add a private member: private List<RSSItem> result; (replace RSSItem here by the type of the collection returned by getFeed).

Then, update doInBackground:

FeedSource f = new HttpFeedSource();
if (f != null)
    return f;
else {
    this.result = f.getFeed(); // Execute getFeed in doInBackground
    return null;
}

Then, in the onPostExecute method, you'll be able to use this private member as this:

RSSItemAdapter adapter = new RSSItemAdapter(getApplicationContext(), R.layout.rssitem, this.result);