public void switchContent(Fragment from, Fragment to) {  
     if (mContent != to) {  
         mContent = to;  
         FragmentTransaction transaction = mFragmentMan.beginTransaction().setCustomAnimations(  
                 android.R.anim.fade_in, R.anim.slide_out);  
         if (!to.isAdded()) {    // 先判斷是否被add過  
             transaction.hide(from).add(R.id.content_frame, to).commit(); // 隱藏當前的fragment，add下一個到Activity中  
         } else {  
             transaction.hide(from).show(to).commit(); // 隱藏當前的fragment，顯示下一個  
         }  
     }  
 }