android 切换fragment的两种方式

使用add方法切换时：
载入Fragment1
Fragment1 onCreate
Fragment1 onCreateView
Fragment1 onStart
Fragment1 onResume
用以下代码切到Fragment2:

1. FragmentTransaction ft = getFragmentManager().beginTransaction();
2. ft.hide(Fragment1);
3. ft.add(R.id.simple_fragment, Fragment2);
4. ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
5. ft.commit();

Fragment1不走任何生命周期,但会调onHiddenChanged方法
Fragment2 onCreate
Fragment2 onCreateView
Fragment2 onStart
Fragment2 onResume
回到Fragment1，Remove Fragment2:

1. FragmentTransaction ft = getFragmentManager().beginTransaction();
2. ft.remove(Fragment2);
3. ft.show(Fragment1);
4. ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
5. ft.commit();

Fragment1还是不走任何生命周期，调onHiddenChanged方法
Fragment2 onPause
Fragment2 onStop
Fragment2 onDestoryView
Fragment2 onDestory
用这种方法切换，Fragment在隐藏时并不会走onDestoryView，所以显示时也不会走onCreateView，所有View都一直保存在内存中。
用replace方法：
载入Fragment1生命周期与上面相同：
Fragment1 onCreate
Fragment1 onCreateView
Fragment1 onStart
Fragment1 onResume
切到Fragment2:

1. FragmentTransaction ft = getFragmentManager().beginTransaction();
2. ft.replace(R.id.simple_fragment, Fragment2);
3. ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
4. ft.commit();

这次的Fragment1走生命周期了
Fragment1 onPause
Fragment1 onStop
Fragment1 onDestoryView
Fragment1 onDestory
Fragment2 onCreate
Fragment2 onCreateView
Fragment2 onStart
Fragment2 onResume
真实打印出来可能是Fragment1和Fragment2混在一起的，可以看到，Fragment1走了onDestory,被完全回收了!
再切回到Fragment1

1. FragmentTransaction ft = getFragmentManager().beginTransaction();
2. ft.replace(R.id.simple_fragment, Fragment1);
3. ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
4. ft.commit();

Fragment1 onCreate
Fragment1 onCreateView
Fragment1 onStart
Fragment1 onResume
Fragment2 onPause
Fragment2 onStop
Fragment2 onDestoryView
Fragment2 onDestory
Fragment1因为已经被回收，又走onCreate，Fragment2被回收。