How to get Context in AsyncTask

[rje7]

I'm trying to expand on the Tab Swipe Application template. I've created a class, say x, which extends AsyncTask which reads from network and update ListView. x.execute(param1) is invoked from the static class DummyFragment.

The problem is i'm confused as to how to pass the context to the following code.

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, values);

Please shed some light as how to pass the context from a static class which extends Fragment.

[AleMonteiro]

Using AsyncTask you can only update the UI(the ListView in this case) on the onPostExecute method. And inside onPostExecute you can call getApplicationContext() to get the context.

[rje7]

    public static class DummySectionFragment extends Fragment {
        public static final String ARG_SECTION_NUMBER = "section_number";
        public DummySectionFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,  Bundle savedInstanceState) {
            new setLV().execute(url);
            View rootView = inflater.inflate(R.layout.fragment_main_dummy, container, false);
            lv_headlines = (ListView) rootView.findViewById(R.id.headlines);
            return rootView;
        }
    }
    public static class setLV extends AsyncTask<URL, Void, String[]>{

        @Override
        protected String[] doInBackground(URL... arg0) {
            //initialisation code for sarr_headlines            
            return null;
        }
        protected void onPostExecute(String[] result) {
            la = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, 0, sarr_headlines);
            lv_headlines.setAdapter(la); 
         }
    }

Hi, Thanks for the reply.

In the above code setLV is an static class. getApplicationContext() does not work when used inside a static class.

setLV is static because the class DummySectionFragment is also static.

Is there any other way?

[rje7]

I've updated the code.. Please find attached. i'm able to get the context by initialization of a static variable. its solved now.

However when i run the code the 1st tab does not show any values populated in the list unless 3rd tab is opened and then returned to tab1. Is this in any way related to the way i process the context?

[AleMonteiro]

Try inverting like this:

public View onCreateView(LayoutInflater inflater, ViewGroup container,  Bundle savedInstanceState) {

            View rootView = inflater.inflate(R.layout.fragment_main_dummy, container, false);
            lv_headlines = (ListView) rootView.findViewById(R.id.headlines);

            new setLV().execute(url);

            return rootView;
        }

[rje7]

yup.. tried that too. Still the listview in tab1 does not load.

[AleMonteiro]

Really don't know... try adding info log in the DummySectionFragment onCreateView to check if the URL is set at that point.

Also, I think that this would be a better code:

public static class setLV extends AsyncTask<URL, Void, String[]>{

        @Override
        protected String[] doInBackground(URL... arg0) {

            String[] headlines=new String[20];

            for(int i=0; i<=19; i++){
                headlines[i]="welcome " + Integer.toString(i);  
            }

            return headlines;
        }
        protected void onPostExecute(String[] result) {
            sarr_headlines = result;
            la = new ArrayAdapter<String>(context, android.R.layout.simple_list_item_1, 0, sarr_headlines);
            lv_headlines.setAdapter(la); 
         }
    }

Inside doInBackground() you shouldn't access anything that is used by the UI Thread.

[rje7]

package in.zeven.indianews2;

import in.zeven.indianews2.R;

import java.util.Locale;

import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends FragmentActivity implements
        ActionBar.TabListener {

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
     * will keep every loaded fragment in memory. If this becomes too memory
     * intensive, it may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    ViewPager mViewPager;

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

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the app.
        mSectionsPagerAdapter = new SectionsPagerAdapter(
                getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager
                .setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {
                        actionBar.setSelectedNavigationItem(position);
                    }
                });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(actionBar.newTab()
                    .setText(mSectionsPagerAdapter.getPageTitle(i))
                    .setTabListener(this));
        }
    }

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

    @Override
    public void onTabSelected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a DummySectionFragment (defined as a static inner class
            // below) with the page number as its lone argument.
            Fragment fragment = new DummySectionFragment();
            Bundle args = new Bundle();
            args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return 3;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            switch (position) {
            case 0:
                return getString(R.string.title_section1).toUpperCase(l);
            case 1:
                return getString(R.string.title_section2).toUpperCase(l);
            case 2:
                return getString(R.string.title_section3).toUpperCase(l);
            }
            return null;
        }
    }

    /**
     * A dummy fragment representing a section of the app, but that simply
     * displays dummy text.
     */
    public static class DummySectionFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        public static final String ARG_SECTION_NUMBER = "section_number";

        public DummySectionFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main_dummy,
                    container, false);
            Object[] object=new Object[2];
            object[0]=rootView;
            object[1]=this.getArguments().getInt(ARG_SECTION_NUMBER);
            new AsyncRead().execute(object);
            return rootView;
        }
    }
    public static class AsyncRead extends AsyncTask<Object, Void, String[]>{
        View view;
        Integer section;
        String[] headlines=new String[20];
        @Override
        protected String[] doInBackground(Object...object) {
            this.view=(View)object[0];
            this.section=(Integer)object[1];
            for(int i=0; i<=19; i++){
                headlines[i]="welcome "+section;    
            }
            return headlines;
        }

        @Override
        protected void onPostExecute(String[] result) {
            //TextView dummyTextView = (TextView) view.findViewById(R.id.section_label);
            //dummyTextView.setText(result[1]);
            ListView lv_headlines = (ListView) view.findViewById(R.id.headlines);
            ArrayAdapter<String> aa = new ArrayAdapter<String>(view.getContext(), android.R.layout.simple_list_item_1, 0, headlines);
            lv_headlines.setAdapter(aa);
         }
    }

}

finally :) its working

Many Thanks for your time.