ViewPager + Fragments - Fragment not shown

Question

I am trying to use a viewpager to display several fragments. At the moment I only have a single fragment but it appears that it is never being instantiated. I tried using pager.setCurrentItem(0) but the getItem method in the adapter is never being called. Does anyone see why my fragment is not loading in the below code?

Main Activity

public class MainActivity extends SherlockFragmentActivity {

MyPagerAdapter adapter;

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

    // Create the FragmentPager Adapter and assign it to the viewpager
    adapter = new MyPagerAdapter( getSupportFragmentManager(), this );
    ViewPager pager = ( ViewPager ) findViewById( R.id.pager );
    pager.setAdapter( adapter );
    pager.setCurrentItem( 0 );

    // Setup the tab page indicator
    TabPageIndicator indicator = ( TabPageIndicator ) findViewById( R.id.indicator );
    indicator.setViewPager( pager );
}

class MyPagerAdapter extends FragmentStatePagerAdapter {
    private SparseArray<Fragment> fragmentPageMap;

    public MyPagerAdapter(FragmentManager fm, Activity context) {
        super( fm );
        fragmentPageMap = new SparseArray<Fragment>();
    }

    @Override
    public Fragment getItem(int index) {
        switch ( index ) {
        case 0:
            if ( fragmentPageMap.get( index ) != null ) {
                SherlockListFragment scheduleFragment =  ScheduleListFragment.newInstance();
                fragmentPageMap.put( index, scheduleFragment );
                return scheduleFragment;
            } else {
                return fragmentPageMap.get( index );
            }
        default:
            return null;
        }
    }

    /*@Override
    public void destroyItem(View container, int index, Object object) {
        super.destroyItem( container, index, object );
        fragmentPageMap.remove( index );
    }*/

    @Override
    public CharSequence getPageTitle(int index) {
        return ( ( ViewPagerPage ) fragmentPageMap.get( index ) ).getTitle();
    }

    @Override
    public int getCount() {
        return fragmentPageMap.size();
    }
}

public interface ViewPagerPage {
    String getTitle();
}

MainActivity Layout

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

<com.viewpagerindicator.TabPageIndicator
    android:id="@+id/indicator"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:textStyle="bold" />

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1" />

</LinearLayout>

ScheduleListFragment

public class ScheduleListFragment extends SherlockListFragment implements ViewPagerPage {

private ScheduleAdapter adapter;
private final String TITLE = "Schedule";

public static ScheduleListFragment newInstance() {
    ScheduleListFragment newFrag = new ScheduleListFragment();
    Bundle args = new Bundle();
    newFrag.setArguments( args );
    return newFrag;
}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate( R.layout.fragment_schedule_list, null );
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate( R.menu.fragment_schedule_list, menu );
}

// Container Activity must implement this interface
public interface OnAddItemClickedListener {
    public void onAddItemClicked();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch ( item.getItemId() ) {
    case R.id.add_item:
        Intent myIntent = new Intent( getActivity(), AddScheduleItemActivity.class );
        startActivityForResult( myIntent, 1 );

        return true;
    default:
        return super.onOptionsItemSelected( item );
    }
}

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated( savedInstanceState );
    setHasOptionsMenu( true );

    adapter = new ScheduleAdapter( getActivity() );

    setListAdapter( adapter );
}

private class SampleItem {
    public String tag;
    public int iconRes;

    public SampleItem(String tag, int iconRes) {
        this.tag = tag;
        this.iconRes = iconRes;
    }
}

public class ScheduleAdapter extends ArrayAdapter<SampleItem> {

    public ScheduleAdapter(Context context) {
        super( context, 0 );
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        if ( convertView == null ) {
            convertView = LayoutInflater.from( getContext() ).inflate( R.layout.results_list_row, null );
        }
        ImageView icon = ( ImageView ) convertView.findViewById( R.id.row_icon );
        icon.setImageResource( getItem( position ).iconRes );
        TextView title = ( TextView ) convertView.findViewById( R.id.row_title );
        title.setText( getItem( position ).tag );

        return convertView;
    }

}

@Override
public String getTitle() {
    return TITLE;
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if ( resultCode == android.app.Activity.RESULT_OK ) {
        String name = ( String ) data.getExtras().get( "TEXT" );
        Toast.makeText( getActivity(), name, Toast.LENGTH_LONG ).show();
    }
}

Fragment Layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ListView
    android:id="@android:id/list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" />

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView" />

</LinearLayout>

Thanks, Nathan

Current Solutions:

Changed the adapters constructor to initialize the first fragment and add it to the internal map. Does anyone see anything wrong with doing this, or a way to improve any of the code posted above? Thanks!

public MyPagerAdapter(FragmentManager fm, Activity context) {
        super( fm );
        fragmentPageMap = new SparseArray<Fragment>();
        SherlockListFragment scheduleFragment = ScheduleListFragment.newInstance();
        fragmentPageMap.put( 0, scheduleFragment );
    }

Answer 1

getCount() is returning 0 in MyPagerAdapter so no Fragment will be created, it should return N if you want N Fragments to be instantiated.

fragmentPageMap is created in the constructor and is empty when getCount() is called and getCount() is called before getItem(index), that is why getCount() returns 0

In this case you don't need a switch because you are instantiating the same Fragment each time. But you would need it if you where instantiating diferent Fragments.

@Override
public Fragment getItem(int index) {
  switch (index) {
    case 0:
      return new Fragment1();
    case 1:
      return new Fragment2();
  }
  return null;
}