在onLoadReset之后savedInstanceState为空，但是如果调用onCreate并且onLoadReset不是（如果设备旋转的情况下），则运行良好

时间：2016-12-07 11:32:23

标签： android-fragments android-recyclerview asynctaskloader

我有一个片段，我使用AsyncTaskLoader从API获取数据，然后使用自定义适配器对两个单独的RecyclerView进行充气。问题是当我点击回收器视图进入该特定位置的detailsActivity然后回到原始Activity时，我发现saveInstanceState为空。但是，如果我旋转我的设备，它的效果非常好。我不认为这是正确的行为。如果它适用于屏幕旋转，那么它也适用于我的问题。

这是我片段的代码：

public class MoviePosterFragment extends Fragment implements LoaderManager.LoaderCallbacks<ArrayList<Movie>> {

private static final int POPULAR_MOVIE_LOADER_ID = 1111;
private static final int UPCOMING_MOVIE_LOADER_ID = 9999;
ArrayList<Movie> popularMovies;
ArrayList<Movie> upcomingMovies;
PopularMoviesAdapter mPopularMoviesAdapter;
UpcomingMovieAdapter mUpcomingMovieAdapter;
RecyclerView mPopularMovieRecyclerView;
RecyclerView mUpcomingMovieRecyclerView;
Uri.Builder uriBuilder;
String savedInstance;
LinearLayoutManager layoutManagerPopularMoviesPoster;
LinearLayoutManager layoutManagerUpcomingMoviesPoster;

public MoviePosterFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.v("############******", "onCreate called");
    if (savedInstanceState == null) {
        popularMovies = new ArrayList<>();
        upcomingMovies = new ArrayList<>();
        savedInstance = "empty";
        Log.v("############******", "onCreate savedInstance is " + savedInstance);
        //First of all check if network is connected or not then only start the loader
        ConnectivityManager connMgr = (ConnectivityManager)
                getActivity().getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            /*
             *fetch data. Get a reference to the LoaderManager, in order to interact with loaders.
            */
            Log.v("############******", "startPopularMoviesLoaderManager called");
            startPopularMoviesLoaderManager();
            Log.v("############******", "startUpcomingMoviesLoaderManager called");
            startUpcomingMoviesLoaderManager();

        }

    } else {
        savedInstance = "not empty";
        Log.v("############******", "onCreate savedInstance is " + savedInstance);
        popularMovies = savedInstanceState.getParcelableArrayList("popularMovies");
        upcomingMovies = savedInstanceState.getParcelableArrayList("upcomingMovies");

    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    Log.v("############******", "onCreateView savedInstance is " + savedInstanceState);
    // Inflate the layout for this fragment
    View rootView = inflater.inflate(R.layout.fragment_movie_posters, container, false);

    /* Code referenced from the @link:
     * "https://guides.codepath.com/android/using-the-recyclerview"
     */
    /*
     * Lookup the recyclerView in activity layout
     */
    mPopularMovieRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerViewPopularMovies);
    mUpcomingMovieRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerViewTopMoviesMovies);

     /*
      * Setup layout manager for items with orientation
      * Also supports `LinearLayoutManager.HORIZONTAL`
      */
    layoutManagerPopularMoviesPoster = new LinearLayoutManager(getActivity(),
            LinearLayoutManager.HORIZONTAL, false);
        /* Optionally customize the position you want to default scroll to */
    layoutManagerPopularMoviesPoster.scrollToPosition(0);
        /* Attach layout manager to the RecyclerView */
    mPopularMovieRecyclerView.setLayoutManager(layoutManagerPopularMoviesPoster);

     /*
      * Setup layout manager for items with orientation
      * Also supports `LinearLayoutManager.HORIZONTAL`
      */
    layoutManagerUpcomingMoviesPoster = new LinearLayoutManager(getActivity(),
            LinearLayoutManager.HORIZONTAL, false);
        /* Optionally customize the position you want to default scroll to */
    layoutManagerUpcomingMoviesPoster.scrollToPosition(0);
        /* Attach layout manager to the RecyclerView */
    mUpcomingMovieRecyclerView.setLayoutManager(layoutManagerUpcomingMoviesPoster);

    SnapHelper snapHelperForPopularMovieRecyclerView = new GravitySnapHelper(Gravity.START);
    snapHelperForPopularMovieRecyclerView.attachToRecyclerView(mPopularMovieRecyclerView);

    SnapHelper snapHelperForUpcomingMovieRecyclerView = new GravitySnapHelper(Gravity.START);
    snapHelperForUpcomingMovieRecyclerView.attachToRecyclerView(mUpcomingMovieRecyclerView);

    /* Code referenced from the @link:
    * "https://guides.codepath.com/android/using-the-recyclerview"
    */

    // Create mPopularMoviesAdapter passing in the sample user data
    mPopularMoviesAdapter = new PopularMoviesAdapter(getActivity(), popularMovies);
    mPopularMoviesAdapter.setMovieData(popularMovies);
    // Attach the mPopularMoviesAdapter to the recyclerview to populate items
    mPopularMovieRecyclerView.setAdapter(mPopularMoviesAdapter);

    // Create mUpcomingMoviesAdapter passing in the sample user data
    mUpcomingMovieAdapter = new UpcomingMovieAdapter(getActivity(), upcomingMovies);
    mUpcomingMovieAdapter.setMovieData(upcomingMovies);
    // Attach the mUpcomingMoviesAdapter to the recyclerview to populate items
    mUpcomingMovieRecyclerView.setAdapter(mUpcomingMovieAdapter);

    return rootView;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    Log.v("############******", "onActivityCreated called and saveInstance is " + savedInstanceState);
    mPopularMoviesAdapter = new PopularMoviesAdapter(getActivity(), popularMovies);
    mUpcomingMovieAdapter = new UpcomingMovieAdapter(getActivity(), upcomingMovies);
    mUpcomingMovieAdapter.setMovieData(upcomingMovies);
    mPopularMoviesAdapter.setMovieData(popularMovies);
    mPopularMovieRecyclerView.setAdapter(mPopularMoviesAdapter);
    mUpcomingMovieRecyclerView.setAdapter(mUpcomingMovieAdapter);
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    Log.v("############******", "onSaveInstanceState called");
    outState.putParcelableArrayList("popularMovies", popularMovies);
    outState.putParcelableArrayList("upcomingMovies", upcomingMovies);
}


private void startPopularMoviesLoaderManager() {
    LoaderManager loaderManager = getLoaderManager();
    Log.v("############******", "initLoader called with id " + POPULAR_MOVIE_LOADER_ID);
    loaderManager.initLoader(POPULAR_MOVIE_LOADER_ID, null, this);
    Log.v("############******", "startPopularMoviesLoaderManager finished");
}

private void startUpcomingMoviesLoaderManager() {
    LoaderManager loaderManager = getLoaderManager();
    Log.v("############******", "initLoader called with id " + UPCOMING_MOVIE_LOADER_ID);
    loaderManager.initLoader(UPCOMING_MOVIE_LOADER_ID, null, this);
    Log.v("############******", "startUpcomingMoviesLoaderManager finished");
}

@Override
public Loader<ArrayList<Movie>> onCreateLoader(int id, Bundle args) {
    if (id == POPULAR_MOVIE_LOADER_ID) {
        Log.v("############******", "onCreateLoader called with id " + POPULAR_MOVIE_LOADER_ID);
        Uri baseUri = Uri.parse(UrlsAndConstants.MoviePosterQuery.DEFAULT_URL);
        Log.v("############", "baseUri is " + baseUri.toString());
        uriBuilder = baseUri.buildUpon();
        Log.v("############", "uriBuilder is " + uriBuilder.toString());
        uriBuilder.appendQueryParameter(API_KEY_PARAM, API_KEY_PARAM_VALUE);
        Log.v("############", "uriBuilder.toString() is " + uriBuilder.toString());
        uriBuilder.appendQueryParameter(SORT_BY_KEY, SORT_BY_POPULARITY_VALUE_DESCENDING);

    } else if (id == UPCOMING_MOVIE_LOADER_ID) {
        Log.v("############", "onCreateLoader called with id " + UPCOMING_MOVIE_LOADER_ID);
        Uri baseUri = Uri.parse("https://api.themoviedb.org/3/movie/upcoming");
        Log.v("############", "baseUri is " + baseUri.toString());
        uriBuilder = baseUri.buildUpon();
        Log.v("############", "uriBuilder is " + uriBuilder.toString());
        uriBuilder.appendQueryParameter(API_KEY_PARAM, API_KEY_PARAM_VALUE);
        Log.v("############", "uriBuilder.toString() is " + uriBuilder.toString());
    }
    return new MoviePosterLoader(getActivity().getApplicationContext(), uriBuilder.toString());
}

@Override
public void onLoadFinished(Loader<ArrayList<Movie>> loader, ArrayList<Movie> incomingMovieArrayList) {
    switch (loader.getId()) {
        case POPULAR_MOVIE_LOADER_ID:
            Log.v("############******", "onLoadFinished called with id " + POPULAR_MOVIE_LOADER_ID);
            if (incomingMovieArrayList.isEmpty()) {
                Log.v("******************", "popularMovies isEmpty");
                return;
            } else {
                popularMovies = incomingMovieArrayList;
                mPopularMoviesAdapter = new PopularMoviesAdapter(getActivity(), popularMovies);
                mPopularMoviesAdapter.setMovieData(popularMovies);
                mPopularMovieRecyclerView.setAdapter(mPopularMoviesAdapter);

            }
            break;
        case UPCOMING_MOVIE_LOADER_ID:
            Log.v("############******", "onLoadFinished called with id " + UPCOMING_MOVIE_LOADER_ID);
            if (incomingMovieArrayList.isEmpty()) {
                Log.v("******************", "popularMovies isEmpty");
                return;
            } else {
                upcomingMovies = incomingMovieArrayList;
                mUpcomingMovieAdapter = new UpcomingMovieAdapter(getActivity(), upcomingMovies);
                mUpcomingMovieAdapter.setMovieData(upcomingMovies);
                mUpcomingMovieRecyclerView.setAdapter(mUpcomingMovieAdapter);
            }
            break;
    }
}

@Override
public void onLoaderReset(Loader<ArrayList<Movie>> loader) {
    Log.v("############******", "onLoaderReset called ");

}

}

正如您在Logcat消息中看到的那样，问题肯定存在。

Logcat消息：

`第一次启动应用时：

12-07 01:37:56.450 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate called
12-07 01:37:56.450 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate savedInstance is empty
12-07 01:37:56.450 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager called
12-07 01:37:56.453 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 1111
12-07 01:37:56.453 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateLoader called with id 1111
12-07 01:37:56.455 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager finished
12-07 01:37:56.455 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager called
12-07 01:37:56.455 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 9999
12-07 01:37:56.455 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager finished
12-07 01:37:56.456 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateView savedInstance is null
12-07 01:37:56.493 9756-9756/me.abhishekraj.showmyshow V/############******: onActivityCreated called and saveInstance is null
12-07 01:37:57.683 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 9999
12-07 01:37:57.731 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 1111
After a popular movie poster is clicked
12-07 01:29:16.062 2256-2256/me.abhishekraj.showmyshow V/############******: onSaveInstanceState called
After coming back from DetailActivity
12-07 01:38:52.785 9756-9756/me.abhishekraj.showmyshow V/############******: onLoaderReset called
12-07 01:38:52.785 9756-9756/me.abhishekraj.showmyshow V/############******: onLoaderReset called
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate called
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate savedInstance is empty
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager called
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 1111
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateLoader called with id 1111
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager finished
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager called
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 9999
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager finished
12-07 01:38:52.851 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateView savedInstance is null
12-07 01:38:52.855 9756-9756/me.abhishekraj.showmyshow V/############******: onActivityCreated called and saveInstance is null
12-07 01:38:53.326 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 9999
12-07 01:38:54.033 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 1111
After a upcoming movie poster is clicked
12-07 01:30:04.572 2256-2256/me.abhishekraj.showmyshow V/############******: onSaveInstanceState called
After coming back from DetailActivity
12-07 01:39:51.672 9756-9756/me.abhishekraj.showmyshow V/############******: onLoaderReset called
12-07 01:39:51.672 9756-9756/me.abhishekraj.showmyshow V/############******: onLoaderReset called
12-07 01:39:51.759 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate called
12-07 01:39:51.759 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate savedInstance is empty
12-07 01:39:51.759 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager called
12-07 01:39:51.759 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 1111
12-07 01:39:51.759 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateLoader called with id 1111
12-07 01:39:51.760 9756-9756/me.abhishekraj.showmyshow V/############******: startPopularMoviesLoaderManager finished
12-07 01:39:51.760 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager called
12-07 01:39:51.760 9756-9756/me.abhishekraj.showmyshow V/############******: initLoader called with id 9999
12-07 01:39:51.760 9756-9756/me.abhishekraj.showmyshow V/############******: startUpcomingMoviesLoaderManager finished
12-07 01:39:51.761 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateView savedInstance is null
12-07 01:39:51.765 9756-9756/me.abhishekraj.showmyshow V/############******: onActivityCreated called and saveInstance is null
12-07 01:39:51.815 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 1111
12-07 01:39:51.817 9756-9756/me.abhishekraj.showmyshow V/############******: onLoadFinished called with id 9999
on rotate
12-07 01:40:18.441 9756-9756/me.abhishekraj.showmyshow V/############******: onSaveInstanceState called
12-07 01:40:18.472 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate called
12-07 01:40:18.472 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate savedInstance is not empty
12-07 01:40:18.478 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateView savedInstance is Bundle[{upcomingMovies=[me.abhishekraj.showmyshow.Movie@c837a9f, me.abhishekraj.showmyshow.Movie@42b07b5, me.abhishekraj.showmyshow.Movie@da99e4a,.......and so on..that means it's not empty
onRotating back
12-07 01:40:48.244 9756-9756/me.abhishekraj.showmyshow V/############******: onSaveInstanceState called
12-07 01:40:48.281 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate called
12-07 01:40:48.281 9756-9756/me.abhishekraj.showmyshow V/############******: onCreate savedInstance is not empty
12-07 01:40:48.286 9756-9756/me.abhishekraj.showmyshow V/############******: onCreateView savedInstance is Bundle[{upcomingMovies=[me.abhishekraj.showmyshow.Movie@c837a9f, me.abhishekraj.showmyshow.Movie@42b07b5, me.abhishekraj.showmyshow.Movie@da99e4a, me.abhishekraj.showmyshow.Movie@67a86d8, me.abhishekraj.showmyshow.Movie@a516a31, me.abhishekraj.showmyshow.Movie@e241e97,.....and so on...that means it's not empty`

那么问题出在哪里？当我从另一个活动返回到此片段时，为什么我得到空白的saveInstanceState，但是为了屏幕旋转，为什么不是null null saveInstanceState，即使在两种情况下都再次创建活动（???）。 谢谢！

修改

如果需要更多代码来获取引用，则可以在以下内容中找到它：Gist

1 个答案:

答案 0 :(得分：0)

如果将主要活动的启动模式用作单顶，这在我的用例中似乎完全可以接受，则可以很容易地解决问题。以下是解决问题后我的manifest.xml的样子：

    <activity
        android:name=".MainActivity"
        android:launchMode="singleTop">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

但是，更好的方法可以是使用Back Stack，这样活动状态可以在被销毁之前保存。我会在使用back-stack解决问题时更新答案，但现在它可以完成工作。

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