Android Fragment onClick button Method

Your activity must have

public void insertIntoDb(View v) {
...
} 

not Fragment .

If you don’t want the above in activity. initialize button in fragment and set listener to the same.

<Button
    android:id="@+id/btn_conferma" // + missing

Then

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

   View view = inflater.inflate(R.layout.fragment_rssitem_detail,
    container, false);
   Button button = (Button) view.findViewById(R.id.btn_conferma);
   button.setOnClickListener(new OnClickListener()
   {
             @Override
             public void onClick(View v)
             {
                // do something
             } 
   }); 
   return view;
}