Android 使用setRetainInstance（true）保留片段实例是如何工作的？

我有一个没有视图的片段，用于承载异步任务。我希望在配置更改（例如方向更改）期间保留片段对象。据我所知，在片段的onCreate（）方法中使用setRetainInstance（true）就足够了。但我的问题是：

首先，让我发布一些我正在使用的代码

“我的活动”在其onCreate（）方法中使用此选项

下面是片段代码的一些示例

class DirectionsFetcherFragment extends Fragment
{
    /* string constants omitted */


    public static DirectionsFetcherFragment newInstance(/*omitted*/)
    {
        DirectionsFetcherFragment instance = new DirectionsFetcherFragment();
        Bundle data = new Bundle();
        /* omitted - adding the necessary data to the bundle */
        instance.setArguments(data);
        return instance;
    }

    public DirectionsFetcherFragment()
    {
        super();
        /* omitted - setting default values for member variables */
    }

    @Override
    public void onCreate(Bundle savedInstance)
    {
        Log.wtf(TAG, "onCreate()");
        super.onCreate(savedInstance);
        setRetainInstance(true);
        Bundle arguments = getArguments();

        /* omitted - other initializations tasks that take place */
    }
}

下面是正在发生的事情。在初始活动创建时，fetcher引用如预期的那样为null，因此我创建了一个新片段并通过事务添加它。但是，当/如果我旋转设备，当活动的onCreate（）方法运行时，fetcher引用为null，findFragmentByTag（）不会返回任何片段。在LogCat中，我可以清楚地看到片段的onDetach（）->onAttach（）方法是为第一个片段运行的，但是由于某种原因，该片段随后被垃圾收集，并创建了一个新片段

以下是LogCat输出：

D/DirectionsViewer﹕ Initializing from intent <<-- Initial activity creation
D/DirectionsViewer﹕ Creating new DirectionsFetcherFragment instance <<-- Fragment creation
A/DirectionsFetcherFragment﹕ onAttach()
A/DirectionsFetcherFragment﹕ onCreate()
V/DirectionsViewer﹕ onStart()
V/DirectionsViewer﹕ onResume()
V/DirectionsViewer﹕ onSaveInstanceState() <<-- Rotationing and saving instance
A/DirectionsFetcherFragment﹕ onDetach() <<-- Fragment correctly detaches
D/DirectionsViewer﹕ Restoring from saved instance <<-- Activity restoration
D/DirectionsViewer﹕ Creating new DirectionsFetcherFragment instance <<-- Why is this happenning, shouldn't I get a reference to the existing fragment?
A/DirectionsFetcherFragment﹕ onAttach()
A/DirectionsFetcherFragment﹕ onCreate()
V/DirectionsViewer﹕ onStart()
V/DirectionsViewer﹕ onResume()
V/DirectionsViewer﹕ Deleting DirectionsViewer instance <<-- This is the old activity that gets garbage collected
A/DirectionsFetcherFragment﹕ Deleting DirectionsFetcherFragment instance <<-- This is the old fragment instance that gets garbage collected

D/DirectionsViewer﹕ 从意图初始化
D/DirectionsViewer﹕ Initializing from intent <<-- Initial activity creation
D/DirectionsViewer﹕ Creating new DirectionsFetcherFragment instance <<-- Fragment creation
A/DirectionsFetcherFragment﹕ onAttach()
A/DirectionsFetcherFragment﹕ onCreate()
V/DirectionsViewer﹕ onStart()
V/DirectionsViewer﹕ onResume()
V/DirectionsViewer﹕ onSaveInstanceState() <<-- Rotationing and saving instance
A/DirectionsFetcherFragment﹕ onDetach() <<-- Fragment correctly detaches
D/DirectionsViewer﹕ Restoring from saved instance <<-- Activity restoration
D/DirectionsViewer﹕ Creating new DirectionsFetcherFragment instance <<-- Why is this happenning, shouldn't I get a reference to the existing fragment?
A/DirectionsFetcherFragment﹕ onAttach()
A/DirectionsFetcherFragment﹕ onCreate()
V/DirectionsViewer﹕ onStart()
V/DirectionsViewer﹕ onResume()
V/DirectionsViewer﹕ Deleting DirectionsViewer instance <<-- This is the old activity that gets garbage collected
A/DirectionsFetcherFragment﹕ Deleting DirectionsFetcherFragment instance <<-- This is the old fragment instance that gets garbage collected