ExpandableListView won't populate

Question

I'm trying to inflate an ExpandableListView in a Fragment and use a setAdapter. I succeed properly when I don't use it in a fragment, but in Fragment, I either get errors (NullPointerException) or the ExpandableListView won't be populated.

package com.stylingandroid.basicactionbar;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ExpandableListView;

public class Friends extends Fragment
{
    private static List<Country> Countries;
    private ExpandableListView expandableListView;
    private CountryAdapter adapter;
    private View V;


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

        V = inflater.inflate( R.layout.frag2, container, false );
        LoadCountries();
        expandableListView = (ExpandableListView) V.findViewById(R.id.expandableListView);
        expandableListView.setAdapter(adapter);
        adapter = new CountryAdapter(this, Countries);

        return V;
    }


    private void LoadCountries() {
        Countries = new ArrayList<Country>();

        ArrayList<String> citiesAustralia = new ArrayList<String>(
                Arrays.asList("Brisbane", "Hobart", "Melbourne", "Sydney"));
        Countries.add(new Country("Australia", citiesAustralia));

        ArrayList<String> citiesChina = new ArrayList<String>(
                Arrays.asList("Beijing", "Chuzhou", "Dongguan", "Shangzhou"));
        Countries.add(new Country("China", citiesChina));
    }
    }

frag2.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent">
    <ExpandableListView
            android:id="@+id/expandableListView"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"/>
</LinearLayout>

package com.stylingandroid.basicactionbar;



import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity
{
    private class MyTabListener implements ActionBar.TabListener
    {
        private Fragment mFragment;
        private final Activity mActivity;
        private final String mFragName;

        public MyTabListener( Activity activity, String fragName )
        {
            mActivity = activity;
            mFragName = fragName;
        }

        @Override
        public void onTabReselected( Tab tab, FragmentTransaction ft )
        {
            // TODO Auto-generated method stub

        }

        @Override
        public void onTabSelected( Tab tab, FragmentTransaction ft )
        {
            mFragment = Fragment.instantiate( mActivity, mFragName );
            ft.add( android.R.id.content, mFragment );
        }

        @Override
        public void onTabUnselected( Tab tab, FragmentTransaction ft )
        {
            ft.remove( mFragment );
            mFragment = null;
        }
    }

    @Override
    public void onCreate( Bundle savedInstanceState )
    {
        super.onCreate( savedInstanceState );       
        Intent intent;

        ActionBar ab = getActionBar();
        ab.setNavigationMode( ActionBar.NAVIGATION_MODE_TABS );

        Tab tab = ab.newTab()
                .setText( R.string.title_param )
                .setTabListener( 
                        new MyTabListener( this, 
                                Param.class.getName() ) );
        ab.addTab( tab );

        intent = new Intent().setClass(this, Friends.class);
        tab = ab.newTab()
                .setText( R.string.title_friends )


                .setTabListener( 
                        new MyTabListener( this, 
                                Friends.class.getName() ) );
        ab.addTab( tab );

        tab = ab.newTab()
                .setText( R.string.title_maps )
                .setTabListener( 
                        new MyTabListener( this, 
                                Maps.class.getName() ) );
        ab.addTab( tab );
    }

    @Override
    public boolean onCreateOptionsMenu( Menu menu )
    {
        getMenuInflater().inflate( R.menu.main, menu );
        return true;
    }

    @Override
    public boolean onOptionsItemSelected( MenuItem item )
    {
        boolean ret;
        if (item.getItemId() == R.id.menu_settings)
        {
            // Handle Settings
            ret = true;
        } else
        {
            ret = super.onOptionsItemSelected( item );
        }
        return ret;
    }
}

CountryAdapter:

package com.stylingandroid.basicactionbar;

import android.R;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

import java.util.List;

public class CountryAdapter extends BaseExpandableListAdapter {
    private List<Country> countries;
    private LayoutInflater inflater;

    public CountryAdapter(Context context) {
        this.countries = countries;
        inflater = LayoutInflater.from(context);
    }

    public CountryAdapter(Friends friends, List<Country> countries2) {
        // TODO Auto-generated constructor stub
    }

    @Override
    public int getGroupCount() {
        return countries.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return countries.get(groupPosition).getCities().size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return countries.get(groupPosition).getName();
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return countries.get(groupPosition).getCities().get(childPosition);
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.simple_expandable_list_item_1, parent, false);
        }

        ((TextView) convertView).setText(getGroup(groupPosition).toString());
        return convertView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        if(convertView == null) {
            convertView = inflater.inflate(R.layout.simple_list_item_1, parent, false);
        }

        ((TextView)convertView).setText(getChild(groupPosition,childPosition).toString());
        return convertView;
    }

    @Override
    public boolean isChildSelectable(int i, int i2) {
        return false;
    }
}

The part, I guess, that is wrong is there:

public CountryAdapter(Context context) {
    this.countries = countries;
    inflater = LayoutInflater.from(context);
}

The problem is that I don't understand how to use the (Context, context) for the fragment Friends. Any idea?

Thank you in advance! :)

EDIT:

I used the code of Gaurav Vashisth and I can a NullPointerException. Here is the stack trace.

10-12 19:11:52.105: D/dalvikvm(2203): GC_FOR_ALLOC freed 41K, 6% free 2553K/2716K, paused 62ms, total 66ms
10-12 19:11:52.116: I/dalvikvm-heap(2203): Grow heap (frag case) to 3.215MB for 635812-byte allocation
10-12 19:11:52.265: D/dalvikvm(2203): GC_FOR_ALLOC freed 1K, 6% free 3172K/3340K, paused 141ms, total 141ms
10-12 19:11:52.525: D/dalvikvm(2203): GC_CONCURRENT freed <1K, 5% free 3178K/3340K, paused 8ms+176ms, total 264ms
10-12 19:11:53.405: D/libEGL(2203): loaded /system/lib/egl/libEGL_emulation.so
10-12 19:11:53.495: D/(2203): HostConnection::get() New Host Connection established 0x2a155620, tid 2203
10-12 19:11:53.616: D/libEGL(2203): loaded /system/lib/egl/libGLESv1_CM_emulation.so
10-12 19:11:53.625: D/libEGL(2203): loaded /system/lib/egl/libGLESv2_emulation.so
10-12 19:11:53.725: W/EGL_emulation(2203): eglSurfaceAttrib not implemented
10-12 19:11:53.766: D/OpenGLRenderer(2203): Enabling debug mode 0
10-12 19:12:11.858: D/AndroidRuntime(2203): Shutting down VM
10-12 19:12:11.858: W/dalvikvm(2203): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
10-12 19:12:11.906: E/AndroidRuntime(2203): FATAL EXCEPTION: main
10-12 19:12:11.906: E/AndroidRuntime(2203): java.lang.NullPointerException
10-12 19:12:11.906: E/AndroidRuntime(2203):     at com.stylingandroid.basicactionbar.CountryAdapter.getGroupCount(CountryAdapter.java:26)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.widget.ExpandableListConnector.getCount(ExpandableListConnector.java:397)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.widget.ListView.setAdapter(ListView.java:462)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.widget.ExpandableListView.setAdapter(ExpandableListView.java:470)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at com.stylingandroid.basicactionbar.Friends.onCreateView(Friends.java:32)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.Fragment.performCreateView(Fragment.java:1695)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.BackStackRecord.run(BackStackRecord.java:682)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.os.Handler.handleCallback(Handler.java:725)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.os.Handler.dispatchMessage(Handler.java:92)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.os.Looper.loop(Looper.java:137)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at android.app.ActivityThread.main(ActivityThread.java:5041)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at java.lang.reflect.Method.invokeNative(Native Method)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at java.lang.reflect.Method.invoke(Method.java:511)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-12 19:12:11.906: E/AndroidRuntime(2203):     at dalvik.system.NativeStart.main(Native Method)
10-12 19:17:12.528: I/Process(2203): Sending signal. PID: 2203 SIG: 9

EDIT 2: With the following code, I get the NullPointerException, stack trace above modified.

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

    LoadCountries();
    V = inflater.inflate( R.layout.frag2, container, false );
    expandableListView = (ExpandableListView) V.findViewById(R.id.expandableListView);

    adapter = new CountryAdapter(getActivity(), Countries);
    expandableListView.setAdapter(adapter);
    return V;
}

CountryAdapter:

private List<Country> countries;
private LayoutInflater inflater;

public CountryAdapter(Context context, List<Country> contries) {
    this.countries = countries;
    inflater = LayoutInflater.from(context);
}

what is line 27 `CountryAdapter.java` and do you get the exception after making the corrections suggested — Raghunandan, Oct 12 '13 at 18:52
From the logs I guess countries arraylist was null at that moment. — Gaurav Vashisth, Oct 12 '13 at 18:58
probably that is because countries might not be populated before passing the same to adapter. So moving adapter initialization to the end of `LoadCountries()` is better — Raghunandan, Oct 12 '13 at 18:59

Raghunandan · Answer 1 · 2013-10-12T18:58:25.847

Use getActivity()

public final Activity getActivity ()

Added in API level 11
Return the Activity this fragment is currently associated with.

Replace

  adapter = new CountryAdapter(this, Countries);

By

  adapter = new CountryAdapter(getActivity(), Countries);

Also you need to reverse

 expandableListView.setAdapter(adapter);
 adapter = new CountryAdapter(this, Countries);

to

 adapter = new CountryAdapter(getActivity(), Countries);
 expandableListView.setAdapter(adapter);

Edit:

Also it would be better to change to

  private void LoadCountries() {
    Countries = new ArrayList<Country>();

    ArrayList<String> citiesAustralia = new ArrayList<String>(
            Arrays.asList("Brisbane", "Hobart", "Melbourne", "Sydney"));
    Countries.add(new Country("Australia", citiesAustralia));

    ArrayList<String> citiesChina = new ArrayList<String>(
            Arrays.asList("Beijing", "Chuzhou", "Dongguan", "Shangzhou"));
    Countries.add(new Country("China", citiesChina));
    adapter = new CountryAdapter(getActivity(), Countries);
    expandableListView.setAdapter(adapter);

   }

Gaurav Vashisth · Accepted Answer · 2013-10-12T19:15:43.883

0

I see that in your onCreateView method you are using the adapter method before initializing it. Use it this way

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

    V = inflater.inflate( R.layout.frag2, container, false );
    LoadCountries();
    expandableListView = (ExpandableListView) V.findViewById(R.id.expandableListView);

    adapter = new CountryAdapter(getActivity(), Countries);
    expandableListView.setAdapter(adapter);
    return V;
}

To get reference of activity in a fragment use getActivity()

Besides it

So that your Adapter's constructor becomes

public CountryAdapter(Context context, List<Country> countries) {
    this.countries = countries;
    inflater = LayoutInflater.from(context);
}

I would also like to point out that according to java conventions method names start with lower case letters. So It would we great if you rename LoadCountries() to loadCountries()

edited Oct 12 '13 at 19:15

answered Oct 12 '13 at 18:30

Gaurav Vashisth

7,547
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35
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Initialize it before using it in expandableListView.setAdapter(adapter) – Gaurav Vashisth Oct 12 '13 at 18:34
yes i agree on that part but you don't need this LayoutInflater `inflater = (LayoutInflater)context.getSystemService (Context.LAYOUT_INFLATER_SERVICE)` and `this` does not refer to activity context – Raghunandan Oct 12 '13 at 18:35
Use it inside the Adapter's constructor. – Gaurav Vashisth Oct 12 '13 at 18:38
even this `inflater = LayoutInflater.from(context)` is fine – Raghunandan Oct 12 '13 at 18:41
I wonder what's the difference between these two APIs to get the LayoutInflater. It would be great if you throw some light on the difference between the two. – Gaurav Vashisth Oct 12 '13 at 18:46
1

http://stackoverflow.com/questions/10776676/what-is-the-difference-between-calling-layoutinflater-directly-and-not – Raghunandan Oct 12 '13 at 18:51
Changing inflater = `LayoutInflater.from(context)`; to `inflater = LayoutInflater.get(context)`; gives this error: The method get(Context) is undefined for the type LayoutInflater – Synor Oct 12 '13 at 19:13
leave it as inflater = LayoutInflater.from(context) – Gaurav Vashisth Oct 12 '13 at 19:16
Please check if you are sending null List to the adapter in the constructor. – Gaurav Vashisth Oct 12 '13 at 19:19
`Toast.makeText(getActivity(),""+expandableListView.getCount(), Toast.LENGTH_LONG).show();` This displays 0. – Synor Oct 12 '13 at 19:32
@NicolasLamoureux did you try the suggestion in my post – Raghunandan Oct 12 '13 at 19:49
@Raghunandan Solved! The problem was `public CountryAdapter(Context context, List contries) {` instrad of `countries`... thanks a lot guys! – Synor Oct 12 '13 at 20:03

ExpandableListView won't populate

2 Answers2