今天使用Fragment的時候，出現了這個錯誤 IllegalStateException: Can not perform this action after onSaveInstanceState：
E/AndroidRuntime(12747): Caused by: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1314)
at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1325)
是在使用FragmentTransition的 commit方法添加一個Fragment的時候出現的，后來在官網找到了相關的
說明：http://developer.android.com/reference/android/app/FragmentTransaction.html#commitAllowingStateLoss()
public abstract int commitAllowingStateLoss ()
Added in API level 11
Like commit()
but allows the commit to be executed after an activity's state is saved. This is dangerous because the commit can be lost if the activity needs to later be restored from its state, so this should only be used for cases where it is okay for the UI state to change unexpectedly on the user.
大致意思是說我使用的 commit方法是在Activity的onSaveInstanceState()之后調用的，這樣會出錯，因為
onSaveInstanceState方法是在該Activity即將被銷毀前調用，來保存Activity數據的，如果在保存玩狀態后
再給它添加Fragment就會出錯。解決辦法就是把commit（）方法替換成 commitAllowingStateLoss()就行
了，其效果是一樣的。
