fragment loads layout but buttons and edittext not active

I use several fragments in a swipe tabs. The last one I created shows up correctly in my app but clicking on buttons and edit text doesn't do anything. I think it is the way I created the fragment in studio.

How can I debug this situation.

I add the java code:

   public class StoreWords extends Fragment {

    public StoreWords() {
        // Required empty public constructor
    }

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.store_words_fragment, container, false);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    initFileSave();
    add_w_edit = (EditText) getActivity().findViewById(R.id.add_diffwords_edit);

    Button add = (Button) getActivity().findViewById(R.id.add_diffwords);
    add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            addWords();
        }
    });

    Button del = (Button) getActivity().findViewById(R.id.remove_diffwords);
    del.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            addWords();
        }
    });
}

and the layout file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.bernard.speechparole.StoreWords"
    >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Large Text"
    android:id="@+id/text_words"
    />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/add_diffwords"
    android:layout_marginLeft="10dp"
    android:text="@string/add"
    android:layout_marginTop="15dp"
    android:layout_below="@id/text_words"
    />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:id="@+id/add_diffwords_edit"
    android:layout_toRightOf="@id/add_diffwords"
    android:layout_marginLeft="30dp"
    android:layout_alignBottom="@id/add_diffwords"
    />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/remove_diffwords"
    android:text="@string/delete"
    android:layout_below="@+id/add_diffwords"
    android:layout_marginTop="15dp"
    android:layout_marginLeft="10dp"
    />

<ScrollView xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:fillViewport="false">

    <ListView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:scrollbarAlwaysDrawVerticalTrack="true"
        android:id="@+id/list_words"
        android:layout_marginTop="10dp"
        android:layout_below="@id/remove_diffwords"
        />
</ScrollView>
</RelativeLayout>

Many thanks in advance!