fragment（2、动态创建）

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 + add
transaction.addToBackStack(null);
transaction.commit();