public void updateButtonsOnKeyboardAndInvalidateOptionsMenu() { getActivity().invalidateOptionsMenu(); ImageButton backspaceOnKeyboard = (ImageButton) getActivity().findViewById(R.id.formula_editor_keyboard_delete); if (!formulaEditorEditText.isThereSomethingToDelete()) { backspaceOnKeyboard.setAlpha(255 / 3); backspaceOnKeyboard.setEnabled(false); } else { backspaceOnKeyboard.setAlpha(255); backspaceOnKeyboard.setEnabled(true); } }