Question

The following is running on an Android 1.6 so I’m using the compatibility package for fragments. In the following TestFragment is a static nested class:

public class FragmentTestActivity extends FragmentActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

public static class TestFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        TextView result = new TextView(getActivity());
        result.setText("Hello TestFragment");
        return result;
    }
}

}

The main.xml file:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent" android:layout_height="fill_parent">
<fragment class="com.test.FragmentTestActivity$TestFragment"
        android:id="@+id/test"
        android:layout_width="fill_parent" android:layout_height="fill_parent" />
</FrameLayout>

The strange thing is that the container parameter in onCreateView is null.

Now, if I add the fragment programatically like so(just change the onCreate method of the Activity) the container is no longer null. Why?

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Fragment frag = new TestFragment();
    getSupportFragmentManager().beginTransaction().add(android.R.id.content, frag).commit();
}

Answer 1

The documentation mentions that it can be null:

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

[…]

container: If non-null, this is the parent view that the
fragment’s UI should be attached to. The fragment should not add the
view itself, but this can be used to generate the LayoutParams of the
view.

To be clear: you shouldn’t do anything like container.addView(...).