Fragment的声明周期整理

声明周期示意图

Fragment生命周期图：

Fragment与Activity生命周期对比图：

-

-------------------------------------------------------------------

2   生命周期分析

1. 当一个fragment被创建的时候，它会经历以下状态.

• onAttach()
• onCreate()
• onCreateView()
• onActivityCreated()

2. 当这个fragment对用户可见的时候，它会经历以下状态。

• onStart()
• onResume()

3. 当这个fragment进入“后台模式”的时候，它会经历以下状态。

• onPause()
• onStop()

4. 当这个fragment被销毁了（或者持有它的activity被销毁了），它会经历以下状态。

• onPause()
• onStop()
• onDestroyView()
• onDestroy() // 本来漏掉类这个回调，感谢xiangxue336提出。
• onDetach()

5. 就像activitie一样，在以下的状态中，可以使用Bundle对象保存一个fragment的对象。

• onCreate()
• onCreateView()
• onActivityCreated()

6. fragments的大部分状态都和activitie很相似，但fragment有一些新的状态。

• onAttached() —— 当fragment被加入到activity时调用（在这个方法中可以获得所在的activity）。
• onCreateView() —— 当activity要得到fragment的layout时，调用此方法，fragment在其中创建自己的layout(界面)。
• onActivityCreated() —— 当activity的onCreated()方法返回后调用此方法
• onDestroyView() —— 当fragment中的视图被移除的时候，调用这个方法。
• onDetach() —— 当fragment和activity分离的时候，调用这个方法。

一旦activity进入resumed状态（也就是running状态），你就可以自由地添加和删除fragment了。因此，只有当activity在resumed状态时，fragment的生命周期才能独立的运转，其它时候是依赖于activity的生命周期变化的。

------------------------------------------------------------

谷歌文档中关于Fragment声明周期描述的摘录:

Lifecycle

Though a Fragment's lifecycle is tied to its owning activity, it has its own wrinkle on the standard activity lifecycle. It includes basic activity lifecycle methods such asonResume(), but also important are methods related to interactions with the activity and UI generation.

The core series of lifecycle methods that are called to bring a fragment up to resumed state (interacting with the user) are:

1. onAttach(Activity) called once the fragment is associated with its activity.
2. onCreate(Bundle) called to do initial creation of the fragment.
3. onCreateView(LayoutInflater, ViewGroup, Bundle) creates and returns the view hierarchy associated with the fragment.
4. onActivityCreated(Bundle) tells the fragment that its activity has completed its ownActivity.onCreate().
5. onViewStateRestored(Bundle) tells the fragment that all of the saved state of its view hierarchy has been restored.
6. onStart() makes the fragment visible to the user (based on its containing activity being started).
7. onResume() makes the fragment interacting with the user (based on its containing activity being resumed).

As a fragment is no longer being used, it goes through a reverse series of callbacks:

1. onPause() fragment is no longer interacting with the user either because its activity is being paused or a fragment operation is modifying it in the activity.
2. onStop() fragment is no longer visible to the user either because its activity is being stopped or a fragment operation is modifying it in the activity.
3. onDestroyView() allows the fragment to clean up resources associated with its View.
4. onDestroy() called to do final cleanup of the fragment's state.
5. onDetach() called immediately prior to the fragment no longer being associated with its activity.