frament可以由自动添加，主要代码如下：

FragmentManager fm = getSupportFragmentManager();  FragmentTransaction transaction = fm.beginTransaction();  mDemo = new DemoFragment();transaction.replace(R.id.fragment_content, mDemo);transaction.commit();

同时可以对每次fragment的操作增加回退栈，增加后back键的操作将首先处理fragment的回退，如下：

FragmentManager fm = getSupportFragmentManager();  FragmentTransaction transaction = fm.beginTransaction();  mDemo = new DemoFragment();transaction.replace(R.id.fragment_content, mDemo);//replace = remove + addtransaction.addToBackStack(null);transaction.commit();