使用自定义Loader时,未在ViewPager片段上调用onResume()

Question

精简版:

我有保持一个片段ViewPager显示其他两个片段,让我们称他们FragmentOne和FragmentTwo.当启动应用程序时,该应用程序FragmentOne是可见的并且FragmentTwo在屏幕外,只有在向左滑动视图时才可见.

通常onStart(),onResume()应用程序启动后立即立即调用这两个片段.

我遇到的问题是当FragmentOne启动自定义时,Loader然后onResume()在FragmentTwo它变得完全可见之前不会被调用.

问题:

这是我的代码问题还是Android支持库中的错误？(该库的修订版12没有出现问题,它从修订版13开始.)

如果它是修订版13和18中的错误,是否有解决方法？

我的自定义有问题Loader吗？

长版:

我已经构建了一个演示该问题的示例应用程序.我试图将代码减少到最低限度,但它仍然很多,所以请耐心等待.

我有一个MainActivity加载a MainFragment创建一个ViewPager.对于我的应用程序来说,ViewPager由Fragment而不是Activity维护是很重要的.

MainFragment创建一个FragmentPagerAdapter反过来创建片段FragmentOne和FragmentTwo.

让我们从有趣的位开始,两个片段:

FragmentOne是一个ListFragment使用自定义Loader加载内容:

public class FragmentOne extends ListFragment implements LoaderCallbacks<List<String>> {
    private ArrayAdapter<String> adapter;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1);
        setListAdapter(adapter);

        setEmptyText("Empty");
    }

    @Override
    public void onResume() {
        super.onResume();

        // initializing the loader seems to cause the problem!
        getLoaderManager().initLoader(0, null, this);
    }

    @Override
    public Loader<List<String>> onCreateLoader(int id, Bundle args) {
        return new MyLoader(getActivity());
    }

    @Override
    public void onLoadFinished(Loader<List<String>> loader, List<String> data) {
        adapter.clear();
        adapter.addAll(data);
    }

    @Override
    public void onLoaderReset(Loader<List<String>> loader) {
        adapter.clear();
    }

    public static class MyLoader extends AsyncTaskLoader<List<String>> {
        public MyLoader(Context context) {
            super(context);
        }

        @Override
        protected void onStartLoading() {
            forceLoad();
        }

        @Override
        public List<String> loadInBackground() {
            return Arrays.asList("- - - - - - - - - - - - - - - - - - - foo",
                    "- - - - - - - - - - - - - - - - - - - bar",
                    "- - - - - - - - - - - - - - - - - - - baz");
        }
    }
}

这Loader似乎导致了这个问题.注释掉initLoader行会使片段生命周期再次按预期工作.

FragmentTwo根据是否onResume()已调用更改其内容:

public class FragmentTwo extends Fragment {
    private TextView text;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        text = new TextView(container.getContext());
        text.setText("onCreateView() called");
        return text;
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.i("Fragment2", "onResume() called");
        text.setText("onResume() called");
    }
}

这是无聊的代码.

MainActivity:

public class MainActivity extends FragmentActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Fragment fragment = new MainFragment();
        getSupportFragmentManager().beginTransaction().add(R.id.container, fragment).commit();
    }
}

布局activity_main:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

MainFragment:

public class MainFragment extends Fragment {
    private ViewPager viewPager;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View layout = inflater.inflate(R.layout.frag_master, container, false);
        viewPager = (ViewPager) layout.findViewById(R.id.view_pager);
        return layout;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        viewPager.setAdapter(new MyPagerAdapter(getChildFragmentManager()));
    }

    private static final class MyPagerAdapter extends FragmentPagerAdapter {
        public MyPagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public Fragment getItem(int position) {
            if (position == 0)
                return new FragmentOne();
            else
                return new FragmentTwo();
        }
    }
}

布局frag_master:

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/view_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

Answer 1

它似乎是支持库中的一个错误.下面的更改解决了这个问题.

// FragmentOne.java

@Override
public void onResume() {
    super.onResume();
    Handler handler = getActivity().getWindow().getDecorView().getHandler();
    handler.post(new Runnable() {
        @Override public void run() {
            // initialize the loader here!
            getLoaderManager().initLoader(0, null, FragmentOne.this);
        }
    });
}