1. Fragment不管是是被另一个Fragment add还是replace，fragment都不会被销毁，只是当add的时候第一个fragment不会销毁视图，当replace的时候，第一个fragment会被销毁视图。
2. 当fragment被Add到Activity的时候，fragment的生命周期方法才会执行。所以想fragment中传值可以这样：
Fragment fragment = new Fragment();
// 这个value值可以在fragment的生命周期方法中使用。
fragment.setValue(value);
transation.add(fragment);
官方参考地址：https://developer.android.google.cn/guide/components/fragments.html
配图一张：
activity连续add两个Fragment然后回退
06-04 12:50:36.074 23734-23734/com.dahai.m1 E/mainActivity: create
06-04 12:50:36.120 23734-23734/com.dahai.m1 E/main1Test1Fragment: attach
06-04 12:50:36.120 23734-23734/com.dahai.m1 E/main1Test1Fragment: create
06-04 12:50:36.121 23734-23734/com.dahai.m1 E/main1Test1Fragment: createView
06-04 12:50:36.125 23734-23734/com.dahai.m1 E/main1Test1Fragment: activityCreated
06-04 12:50:36.128 23734-23734/com.dahai.m1 E/main1Test1Fragment: start
06-04 12:50:36.128 23734-23734/com.dahai.m1 E/mainActivity: start
06-04 12:50:36.130 23734-23734/com.dahai.m1 E/mainActivity: resume
06-04 12:50:36.130 23734-23734/com.dahai.m1 E/main1Test1Fragment: resume
06-04 12:51:34.825 23734-23734/com.dahai.m1 E/main1Test2Fragment: attach
06-04 12:51:34.826 23734-23734/com.dahai.m1 E/main1Test2Fragment: create
06-04 12:51:34.829 23734-23734/com.dahai.m1 E/main1Test2Fragment: activityCreated
06-04 12:51:34.829 23734-23734/com.dahai.m1 E/main1Test2Fragment: start
06-04 12:51:34.829 23734-23734/com.dahai.m1 E/main1Test2Fragment: resume
06-04 12:52:37.058 23734-23734/com.dahai.m1 E/main1Test2Fragment: pause
06-04 12:52:37.058 23734-23734/com.dahai.m1 E/main1Test2Fragment: stop
06-04 12:52:37.058 23734-23734/com.dahai.m1 E/main1Test2Fragment: destroyView
06-04 12:52:37.058 23734-23734/com.dahai.m1 E/main1Test2Fragment: destroy
06-04 12:52:37.058 23734-23734/com.dahai.m1 E/main1Test2Fragment: detach
先add后replace
06-04 14:34:41.166 23734-23734/com.dahai.m1 E/mainActivity: create
06-04 14:34:41.174 23734-23734/com.dahai.m1 E/main1Test1Fragment: attach
06-04 14:34:41.174 23734-23734/com.dahai.m1 E/main1Test1Fragment: create
06-04 14:34:41.174 23734-23734/com.dahai.m1 E/main1Test1Fragment: createView
06-04 14:34:41.175 23734-23734/com.dahai.m1 E/main1Test1Fragment: activityCreated
06-04 14:34:41.175 23734-23734/com.dahai.m1 E/main1Test1Fragment: start
06-04 14:34:41.175 23734-23734/com.dahai.m1 E/mainActivity: start
06-04 14:34:41.176 23734-23734/com.dahai.m1 E/mainActivity: resume
06-04 14:34:41.177 23734-23734/com.dahai.m1 E/main1Test1Fragment: resume
06-04 14:35:44.183 23734-23734/com.dahai.m1 E/main1Test2Fragment: attach
06-04 14:35:44.183 23734-23734/com.dahai.m1 E/main1Test2Fragment: create
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test2Fragment: activityCreated
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test2Fragment: start
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test2Fragment: resume
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test1Fragment: pause
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test1Fragment: stop
06-04 14:35:44.184 23734-23734/com.dahai.m1 E/main1Test1Fragment: destroyView
06-04 14:36:42.711 23734-23734/com.dahai.m1 E/main1Test1Fragment: createView
06-04 14:36:42.712 23734-23734/com.dahai.m1 E/main1Test1Fragment: activityCreated
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test1Fragment: start
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test1Fragment: resume
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test2Fragment: pause
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test2Fragment: stop
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test2Fragment: destroyView
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test2Fragment: destroy
06-04 14:36:42.713 23734-23734/com.dahai.m1 E/main1Test2Fragment: detach
