动态添加片段

嗨，我是android的新手，正在尝试将内容动态添加到中Fragment。

我Fragments里面有两个Activity。第一点指向第二点，如下所示：

public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_welcome,
                container, false);
        Button searchActivityBtn = (Button) rootView.findViewById(R.id.SearchActivityBtn);

        searchActivityBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("##SecondActivity", "search btn click");
                getFragmentManager().beginTransaction()
                    .replace(R.id.welcome_fragment, new searchAnnouncementsFragment()).addToBackStack(null).commit();       
            }
        });                     
        return rootView;
    }
}

第二个Fragment class是

    public static class searchAnnouncementsFragment extends Fragment {

    public searchAnnouncementsFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_search,
                container, false);          
        return rootView;
    }

    //public void onStart(){
    // super.onStart();
    // RelativeLayout root = (RelativeLayout) getActivity().findViewById(R.id.annunciContainer);
    // Log.d("##onstart", "root:" + (root == null));
    //}

}

正如你可以看到我试图做的东西onStart method，但我一直一堆错误，R.id.annunciContainer是id的fragment_search.xml layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:id ="@+id/annunciContainer"
android:layout_width="match_parent"
android:layout_height="match_parent" 
android:background="@color/white" >

我试图做到的，是动态像其他元素添加FrameLayout到我的Fragment（由上述表示的RelativeLayout）。

任何想法？