在我的项目，我本来用这个方案：

In my project, I originally use this scheme:

活动 A （UI）>片段 B （非UI）>适配器+的AsyncTask

Activity A (UI) > Fragment B (non-UI) > Adapter + AsyncTask B 保留与 setRetainInstance（真）和更新 A UI A 实例 B 与 getFragmentManager（）

B retained with setRetainInstance(true) and updating A UI A instantiate B with getFragmentManager()

不过，我现在需要使用的UI片段，所以我想利用这个方案：

But I now need to use UI Fragments, so I thought to use this scheme:

活动 A >片段 B （UI）>片段 C （非UI）>适配器+的AsyncTask

Activity A > Fragment B (UI) > Fragment C (non-UI) > Adapter + AsyncTask C 保留与 setRetainInstance（真）和更新 B UI B 实例 C 与 getChildFragmentManager（）

C retained with setRetainInstance(true) and updating B UI B instantiate C with getChildFragmentManager()

但似乎不可能的：

Caused by: java.lang.IllegalStateException:
    Can't retain fragements that are nested in other fragments

我试图实例 C 与 getFragmentManager（）而不是 getChildFragmentManager（），但我遇到了一些问题。

I tried to instantiate C with getFragmentManager() instead of getChildFragmentManager() but I had some problems.

什么是保留的对象，并在片段管理AsyncTasks的最佳实践？

What is the best practice to retain objects and manage AsyncTasks in a Fragment?

推荐答案

我终于开发出小帮手类：

I finally develop a little helper class:

public class RetainFragment<F extends Fragment> extends Fragment {

    private static <F extends Fragment> String tag(F ui, Object id) {
        return ui.getClass().getName() + id.toString();
    }

    public static <F extends Fragment> Fragment get(F ui, Object id) {
        return ui.getFragmentManager().findFragmentByTag(tag(ui, id));
    }

    public F ui;
    public Object id;

    @Override
    public void onCreate(Bundle state) {
        super.onCreate(state);
        setRetainInstance(true);
    }

    public void link(F ui, Object id) {
        this.id = id;
        this.ui = ui;
        if (get(ui, id) == null) {
            ui.getFragmentManager()
              .beginTransaction()
              .add(this, tag(ui, id))
              .commit();
        }
    }

    public void unlink() {
        if (get(ui, id) != null) {
            ui.getFragmentManager()
              .beginTransaction()
              .remove(this)
              .commit();
        }
        ui = null;
        id = null;
    }

}

而现在，在UI片段，我只写：

And now, in UI Fragments, I only write:

public class UiFragment extends Fragment {

    private static class Retain extends RetainFragment<UiFragment> {
        private MyAsyncTask task;   // Objects to retain over
        private MyAdapter adapter;  // configuration changes
    }

    private Retain retain;

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        retain = (Retain) Retain.get(this, 0);
        if (retain == null) {
            retain = new Retain();
            // Retained objects initialization
            retain.adapter = new MyAdapter();
        }
        retain.link(this, 0);
    }

    @Override
    public void onDetach() {
        if (isRemoving()) {
            // Retained objects terminate
            if (retain.task != null) {
                retain.task.cancel(true);
            }
            retain.unlink();
        }
        super.onDetach();
    }

    private void update() {
        if (!isDetached()) {
            // Update UI fragment
        }
    }

}

而在 retain.task.onPostExecute（）：

retain.ui.update(); // Reference to the last ui fragment instance linked

和推出的UI片段启动任务：

And to launch the task at UI fragment startup:

private static class Retain extends RetainFragment<UiFragment> {
    private MyAsyncTask task;   // Objects to retain over
    private MyAdapter adapter;  // configuration changes

    @Override
    public void onCreate(Bundle state) {
        super.onCreate(state);
        ui.onRetainCreated();
    }
}

private void onRetainCreated() {
    retain.task = new MyAsyncTask() {
        @Override
        protected void onPostExecute(Void result) {
            retain.ui.update();
        }
    };
    retain.task.execute();
}