android中fragment在後臺回收時的生命週期
阿新 • • 發佈：2019-01-10
頁面如下：activity可以切換fragment1，fragment2，初始狀態是fragment2，切fragment1的時候回給fragment1傳值，在實際測試中，發現app切後臺再進來時，傳的這個資料會報空。
先看宣告週期，開始的時候的：
03-15 10:20:19.378 14280-14280/com.dxxx.testfragmentcarsh E/activity: onCreate 03-15 10:20:19.414 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onAttach 03-15 10:20:19.414 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onCreate 03-15 10:20:19.420 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onCreateView 03-15 10:20:19.423 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onActivityCreated 03-15 10:20:19.423 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onViewStateRestored 03-15 10:20:19.424 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onStart 03-15 10:20:19.424 14280-14280/com.dxxx.testfragmentcarsh E/activity: onStart 03-15 10:20:19.424 14280-14280/com.dxxx.testfragmentcarsh E/activity: onResume 03-15 10:20:19.424 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onResume
很正常，跟想象的一樣，再切換到fragment1看看：
03-15 10:20:44.103 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onAttach 03-15 10:20:44.103 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onCreate 03-15 10:20:44.104 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onPause 03-15 10:20:44.104 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onDestroyView 03-15 10:20:44.105 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onDestroy 03-15 10:20:44.105 14280-14280/com.dxxx.testfragmentcarsh E/Fragment2: onDetach 03-15 10:20:44.107 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onCreateView 地址是：Fragment1{f1254d9 #1 id=0x7f0b0061} 03-15 10:20:44.117 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onActivityCreated 03-15 10:20:44.117 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onViewStateRestored 03-15 10:20:44.117 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onStart 03-15 10:20:44.117 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onResume
還是很正常，再後臺關閉下再看：
03-15 10:21:22.211 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onPause 03-15 10:21:22.212 14280-14280/com.dxxx.testfragmentcarsh E/activity: onPause 03-15 10:21:22.277 14280-14280/com.dxxx.testfragmentcarsh E/Fragment1: onSaveInstanceState 03-15 10:21:22.278 14280-14280/com.dxxx.testfragmentcarsh E/activity: onStop
再從前臺回來下：
03-15 10:22:29.515 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onAttach
03-15 10:22:29.515 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onCreate
03-15 10:22:29.781 16099-16099/com.dxxx.testfragmentcarsh E/activity: onCreate
03-15 10:22:29.796 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onCreateView 地址是：Fragment1{30bef2a1 #1 id=0x7f0b0061}
03-15 10:22:29.799 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onActivityCreated
03-15 10:22:29.799 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onViewStateRestored
03-15 10:22:29.806 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onAttach
03-15 10:22:29.806 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onCreate
03-15 10:22:29.811 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onCreateView
03-15 10:22:29.813 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onActivityCreated
03-15 10:22:29.813 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onViewStateRestored
03-15 10:22:29.813 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onStart
03-15 10:22:29.813 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onStart
03-15 10:22:29.813 16099-16099/com.dxxx.testfragmentcarsh E/activity: onStart
03-15 10:22:29.818 16099-16099/com.dxxx.testfragmentcarsh E/activity: onResume
03-15 10:22:29.818 16099-16099/com.dxxx.testfragmentcarsh E/Fragment1: onResume
03-15 10:22:29.818 16099-16099/com.dxxx.testfragmentcarsh E/Fragment2: onResume會看到fragment1和fragment2都被重新例項化了，頁面中也能看到fragment1和fragment2.注意：這裡沒有做傳值的處理，否則就會發現fragment的那個傳的引數空指標了！
這裡因為activity被回收了，他在onsaveinstanc中儲存了頁面的資料，然後再次到前臺會進行恢復，activity恢復會走activity的oncraet方法，也就是把fragment2顯示出來，但是他在被銷燬前儲存了fragmen1的狀態，所有也去走了fragemnt1的宣告週期，但是傳的那個資料，已經不在了，就報空了。
解決辦法就是重寫activity的 onSavaInstance方法，直接寫空，那麼狀態就不會被儲存了。