After screen rotation, findFragmentById() returns a fragment, even if there's no such ID inside the layout

Question

I have one layout in two orientations - 1 landscape and 1 portrait.

/layout-land/main.xml has two fragments:

• <fragment android:id="@+id/fragment1" .. />
• <fragment android:id="@+id/fragment2" .. />

/layout/main.xml has only one fragment:

• <fragment android:id="@+id/fragment1" .. />

Here's the MainActivity.java:

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

    firstFragment = (FirstFragment) getFragmentManager().findFragmentById(R.id.fragment1);
    secondFragment = (SecondFragment) getFragmentManager().findFragmentById(R.id.fragment2);
}

Next, I start the MainActivity.java in landscape mode. In this case,

• Both firstFragment and secondFragment refers to the fragments in the layout layout-land/main.xml

Then I rotate the screen to portrait mode, and the layout file layout/main.xml should be loaded. In this case,

• firstFragment refers to the R.id.fragment1
• secondFragment referes to a non-existant fragment. Accessing any elements inside this throws a NullPointerException. (To be more precise, secondFragment is not null here)

How this secondFragment is initialized when there's no fragment defined inside the layout?

---

Edit: Reason found on Android Developer Documentation at http://developer.android.com/training/basics/fragments/creating.html:

When a configuration change causes the activity hosting these fragments to restart, its new instance may use a different layout that doesn't include the same fragments as the previous layout. In this case all of the previous fragments will still be instantiated and running in the new instance. However, any that are no longer associated with a tag in the view hierarchy will not have their content view created and will return false from isInLayout(). (The code here also shows how you can determine if a fragment placed in a container is no longer running in a layout with that container and avoid creating its view hierarchy in that case.)

Answer 1

You can check like below : I assume that you have Fragment1 class for the fragment you get by findFragmentById

Fragment1 frg1 =getFragmentManager().findFragmentById(R.id.FrgDetalleEvento);
boolean hayDetalle = ( frg1!= null && frg1.isInLayout());

It solved the same problem with me, hope it helpful for every of you

Answer 2

maybe it's too late, but I leave it for future programmers with this problem, I had a similar problem and solved it this way.

Logic: Check the screen orientation, and call findViewById(R.id.fragment2) only if the screen is on landscape mode. Otherwise start a new intent to the other screen

Non working code;

@Override
public void onEventoSeleccionado(Evento e) {

    boolean hayDetalle = (getFragmentManager().findFragmentById(R.id.FrgDetalleEvento) != null);

            if(hayDetalle) {
                SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy hh:mm",Locale.ENGLISH);
                Log.i("EOLog", "Hay Detalle");
                ((DetalleEventoFragment)getFragmentManager().findFragmentById(R.id.FrgDetalleEvento)).mostrarDetalle(Long.toString(e.getId()),formatter.format(e.getFecha()));
            }
            else {
                Log.i("EOLog", "No hay detalle");           
                Intent i = new Intent(this,DetalleEventoActivity.class);                                        
                Bundle b = new Bundle();
                b.putLong("IDEV", e.getId());           
                b.putLong("FECHA", e.getFecha());           
                i.putExtras(b);
                startActivity(i);
            }

}

Working code:

@Override
public void onEventoSeleccionado(Evento e) {

      int orientation = getResources().getConfiguration().orientation;

            if(orientation == Configuration.ORIENTATION_LANDSCAPE) {
                SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy hh:mm",Locale.ENGLISH);
                Log.i("EOLog", "Hay Detalle");
                ((DetalleEventoFragment)getFragmentManager().findFragmentById(R.id.FrgDetalleEvento)).mostrarDetalle(Long.toString(e.getId()),formatter.format(e.getFecha()));
            }
            else if(orientation == Configuration.ORIENTATION_PORTRAIT) {
                Log.i("EOLog", "No hay detalle");           
                Intent i = new Intent(this,DetalleEventoActivity.class);                                        
                Bundle b = new Bundle();
                b.putLong("IDEV", e.getId());           
                b.putLong("FECHA", e.getFecha());           
                i.putExtras(b);
                startActivity(i);
            }else
            {
                Log.i("EOLog", "Dispositivo erroneo");
            }

}

I hope that is helpful