Java 无法在房间数据库中插入值

我正在尝试插入有关电影的信息，但出现以下错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void kawi15.myapplication.database.DatabaseViewModel.addWatchlistMovie(info.movito.themoviedbapi.model.MovieDb)' on a null object reference

我确信这部电影不是空的，因为我有Toast，它显示了关于这部电影的信息

我发现我需要在OnCreate（）中初始化

DatabaseViewModel

：

但我在OnCreate和OnCreateView中尝试了这一点，并在“this”的两个错误中尝试了这一点：

new ViewModelProvider(this)

我试着把getContext（）或其他东西放在那里，但这里什么都不起作用

这是我的实体类：

@Entity
public class Watchlist {
    @PrimaryKey
    @ColumnInfo(name = "id")
    private int movieId;

    @ColumnInfo(name = "movie_title")
    private String movieTitle;

    @ColumnInfo(name = "poster_path")
    private String posterPath;

    @ColumnInfo(name = "overview")
    private String overview;

    @ColumnInfo(name = "release_date")
    private String releaseDate;

and getters and setters for all

我的刀类：

@Dao
public interface WatchlistDao {
    @Query("SELECT * FROM watchlist ORDER BY movie_title ASC")
    List<Watchlist> getAll();

    @Insert
    void addMovie(Watchlist watchlistMovie);
}

我要从列表中单击要插入数据库的电影的片段类：

public class FragmentOne extends Fragment /*implements CustomAdapter.ListItemClickListener*/{

    private static RecyclerView.Adapter adapter;
    private RecyclerView.LayoutManager layoutManager;
    private DatabaseViewModel databaseViewModel;
    private static RecyclerView recyclerView;
    private List<MovieDb> data;
    //private CustomAdapter.ListItemClickListener mOnClickListener;

    public static FragmentOne newInstance() {
        FragmentOne fragment = new FragmentOne();
        return fragment;
    }

    /*@Override
    public void onListItemClick(int position) {
        Toast.makeText(getContext(), data.get(position).getOriginalTitle(), LENGTH_SHORT).show();
    }*/

    public class MovieTask extends AsyncTask<Void, Void, List<MovieDb>> {
        @Override
        protected List<MovieDb> doInBackground(Void... voids) {
            MovieResultsPage movies = new TmdbApi("f753872c7aa5c000e0f46a4ea6fc49b2").getMovies().getUpcoming("en-US", 1, "US");
            List<MovieDb> listMovies = movies.getResults();

            return listMovies;
        }

        @Override
        protected void onPostExecute(List<MovieDb> movieDb) {
            data = movieDb;
            adapter = new CustomAdapter(data);
            ((CustomAdapter) adapter).setOnMovieDbClicked(movieDb2 -> {
                Toast.makeText(getActivity(), movieDb2.getReleaseDate(), LENGTH_SHORT).show();
                databaseViewModel.addWatchlistMovie(movieDb2);
            });
            recyclerView.setAdapter(adapter);
        }
    }

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View returnView = inflater.inflate(R.layout.fragment_one, container, false);


        recyclerView = (RecyclerView) returnView.findViewById(R.id.my_recycler_view);
        recyclerView.setHasFixedSize(true);

        layoutManager = new LinearLayoutManager(getContext());  // ???
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());


        MovieTask mt = new MovieTask();
        mt.execute();

        return returnView;
    }


}

公共类FragmentOne扩展片段/*实现CustomAdapter.ListItemClickListener*/{
专用静态RecyclerView.适配器；
private RecyclerView.LayoutManager LayoutManager；
私有数据库视图模型数据库视图模型；
私有静态RecyclerView RecyclerView；
私人名单数据；
//私有CustomAdapter.ListItemClickListener mOnClickListener；
公共静态碎片一个新实例（）{
FragmentOne片段=新FragmentOne（）；
返回片段；
}
/*@凌驾
公共void onListItemClick（内部位置）{
Toast.makeText（getContext（），data.get（position）.getoriginaltile（），LENGTH_SHORT）.show（）；
}*/
公共类MovieTask扩展了异步任务{
@凌驾
受保护列表背景（无效…无效）{
MovieResultsPage movies=newTMDBAPI（“F753872C7AA5C000E0F46A4 EA6FC49B2”）.getMovies（）.getcoming（“en-US”，1，“US”）；
List listMovies=movies.getResults（）；
返回列表电影；
}
@凌驾
受保护的void onPostExecute（列表movieDb）{
数据=电影数据库；
适配器=新的CustomAdapter（数据）；
（（CustomAdapter）adapter）.setOnMovieDbClicked（movieDb2->{
Toast.makeText（getActivity（），movieDb2.getReleaseDate（），LENGTH_SHORT）.show（）；
databaseViewModel.addWatchlistMovie（movieDb2）；
});
recyclerView.setAdapter（适配器）；
}
}
@凌驾
创建时的公共void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
}
@凌驾
创建视图上的公共视图（布局、充气机、视图组容器、，
Bundle savedInstanceState）{
视图返回视图=充气机。充气（R.layout.fragment\u one，容器，错误）；
recyclerView=（recyclerView）returnView.findViewById（R.id.my\u recycler\u视图）；
recyclerView.setHasFixedSize（true）；
layoutManager=新的LinearLayoutManager（getContext（））；/？？？
recyclerView.setLayoutManager（layoutManager）；
setItemAnimator（新的DefaultItemAnimator（））；
MovieTask mt=新的MovieTask（）；
mt.execute（）；
返回视图；
}
}

和我的适配器类，可能不是必需的：

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder>{

    private List<MovieDb> dataSet;
    private OnMovieDbClicked onMovieDbClicked;


    public void setOnMovieDbClicked(OnMovieDbClicked onMovieDbClicked) {
        this.onMovieDbClicked = onMovieDbClicked;
    }
    //final private ListItemClickListener mOnClickListener;

    public class MyViewHolder extends RecyclerView.ViewHolder /*implements View.OnClickListener*/{

        TextView textViewName;
        TextView textViewVersion;
        ImageView imageViewIcon;
        //private ListItemClickListener mOnClickListener;

        public MyViewHolder(View itemView) {
            super(itemView);
            this.textViewName = (TextView) itemView.findViewById(R.id.text1);
            this.textViewVersion = (TextView) itemView.findViewById(R.id.text2);
            this.imageViewIcon = (ImageView) itemView.findViewById(R.id.imageView);

            itemView.setOnClickListener(view -> {
                int pos = getAdapterPosition();

                if (onMovieDbClicked != null && pos != RecyclerView.NO_POSITION) {
                    MovieDb movieDb = dataSet.get(pos);
                    onMovieDbClicked.movieDbClicked(movieDb);
                }
            });
            //itemView.setOnClickListener(this);
            //itemView.setOnClickListener(CustomAdapter.myOnClickListener);
        }

        /*@Override
        public void onClick(View v) {
            int position = getAdapterPosition();
            mOnClickListener.onListItemClick(position);
        }*/
    }

    public CustomAdapter(List<MovieDb> data /*ListItemClickListener mOnClickListener*/) {
        this.dataSet = data;
        //this.mOnClickListener = mOnClickListener;
    }

    public interface OnMovieDbClicked {
        void movieDbClicked(MovieDb movieDb);
    }

    /*public interface ListItemClickListener{
        void onListItemClick(int position);
    }*/

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent,
                                           int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.cards_layout, parent, false);

        //view.setOnClickListener(FragmentOne.myOnClickListener);

        MyViewHolder myViewHolder = new MyViewHolder(view);
        return myViewHolder;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, final int listPosition) {

        TextView textViewName = holder.textViewName;
        TextView textViewVersion = holder.textViewVersion;
        ImageView imageView = holder.imageViewIcon;
        Glide.with(imageView).load("https://image.tmdb.org/t/p/w500" + dataSet.get(listPosition).getPosterPath()).into(imageView);

        textViewName.setText(dataSet.get(listPosition).getOriginalTitle());
        textViewVersion.setText(dataSet.get(listPosition).getReleaseDate());


    }


    @Override
    public int getItemCount() {
        if(dataSet == null){
            return 0;
        }
        return dataSet.size();
    }
}

公共类CustomAdapter扩展了RecyclerView.Adapter{ 私有列表数据集； 私有OnMovieDbClicked OnMovieDbClicked； public void setOnMovieDbClicked（OnMovieDbClicked OnMovieDbClicked）{ this.onMovieDbClicked=onMovieDbClicked； } //最终私有列表项ClickListener mOnClickListener； 公共类MyViewHolder扩展了RecyclerView.ViewHolder/*实现了View.OnClickListener*/{ TextView textViewName； 文本视图文本视图版本； 图像视图图像视图图标； //私有ListItemClickListener mOnClickListener； 公共MyViewHolder（查看项目视图）{ 超级（项目视图）； this.textViewName=（TextView）itemView.findViewById（R.id.text1）； this.textViewVersion=（TextView）itemView.findViewById（R.id.text2）； this.imageViewIcon=（ImageView）itemView.findViewById（R.id.ImageView）； itemView.setOnClickListener（视图->{ int pos=getAdapterPosition（）； if（onMovieDbClicked！=null&&pos！=RecyclerView.NO_位置）{ MovieDb MovieDb=dataSet.get（pos）； onMovieDbClicked.movieDbClicked（movieDb）； } }); //setOnClickListener（这个）； //setOnClickListener（CustomAdapter.myOnClickListener）； } /*@凌驾 公共void onClick（视图v）{ int position=getAdapterPosition（）； mOnClickListener.onListItemClick（位置）； }*/ } 公共CustomAdapter（列表数据/*ListItemClickListener mOnClickListener*/）{ this.dataSet=数据； //this.mOnClickListener=mOnClickListener； } 已单击MoviedBClick上的公共接口{ 作废movieDbClicked（MovieDb MovieDb）； } /*公共接口ListItemClickListener{ void onListItemClick（内部位置）； }*/ @凌驾 公共MyViewHolder onCreateViewHolder（视图组父级， int视图类型）{ View=LayoutInflater.from（parent.getContext（）） .充气（R.layout.cards\u布局，父级，假）； //view.setOnClickListener（FragmentOne.myOnClickListener）； MyViewHolder MyViewHolder=新的MyViewHolder（视图）； 返回myViewHolder； } @凌驾 公共无效onBindViewHolder（最终MyViewHolder，最终int listPosition）{ TextView textViewName=holder.textViewName； TextView textViewVersion=holder.textViewVersion； ImageView ImageView=holder.imageViewIcon； 使用（图像视图）滑动。加载（“https://image.tmdb.org/t/p/w500“+dataSet.get（listPosition.getPosterPath（））.into（imageView）； textViewName.setText（dataSet.get（listPosition.GetOriginattle（））； textViewVersion.setText（dataSet.get（listPosition.getReleaseDate（））； } @凌驾 public int getItemCount（）{ 如果（数据集==null）{ 返回0； } 返回dataSet.size（）； } } 您尚未初始化y

public class FragmentOne extends Fragment /*implements CustomAdapter.ListItemClickListener*/{

    private static RecyclerView.Adapter adapter;
    private RecyclerView.LayoutManager layoutManager;
    private DatabaseViewModel databaseViewModel;
    private static RecyclerView recyclerView;
    private List<MovieDb> data;
    //private CustomAdapter.ListItemClickListener mOnClickListener;

    public static FragmentOne newInstance() {
        FragmentOne fragment = new FragmentOne();
        return fragment;
    }

    /*@Override
    public void onListItemClick(int position) {
        Toast.makeText(getContext(), data.get(position).getOriginalTitle(), LENGTH_SHORT).show();
    }*/

    public class MovieTask extends AsyncTask<Void, Void, List<MovieDb>> {
        @Override
        protected List<MovieDb> doInBackground(Void... voids) {
            MovieResultsPage movies = new TmdbApi("f753872c7aa5c000e0f46a4ea6fc49b2").getMovies().getUpcoming("en-US", 1, "US");
            List<MovieDb> listMovies = movies.getResults();

            return listMovies;
        }

        @Override
        protected void onPostExecute(List<MovieDb> movieDb) {
            data = movieDb;
            adapter = new CustomAdapter(data);
            ((CustomAdapter) adapter).setOnMovieDbClicked(movieDb2 -> {
                Toast.makeText(getActivity(), movieDb2.getReleaseDate(), LENGTH_SHORT).show();
                databaseViewModel.addWatchlistMovie(movieDb2);
            });
            recyclerView.setAdapter(adapter);
        }
    }

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View returnView = inflater.inflate(R.layout.fragment_one, container, false);


        recyclerView = (RecyclerView) returnView.findViewById(R.id.my_recycler_view);
        recyclerView.setHasFixedSize(true);

        layoutManager = new LinearLayoutManager(getContext());  // ???
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());


        MovieTask mt = new MovieTask();
        mt.execute();

        return returnView;
    }


}

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder>{

    private List<MovieDb> dataSet;
    private OnMovieDbClicked onMovieDbClicked;


    public void setOnMovieDbClicked(OnMovieDbClicked onMovieDbClicked) {
        this.onMovieDbClicked = onMovieDbClicked;
    }
    //final private ListItemClickListener mOnClickListener;

    public class MyViewHolder extends RecyclerView.ViewHolder /*implements View.OnClickListener*/{

        TextView textViewName;
        TextView textViewVersion;
        ImageView imageViewIcon;
        //private ListItemClickListener mOnClickListener;

        public MyViewHolder(View itemView) {
            super(itemView);
            this.textViewName = (TextView) itemView.findViewById(R.id.text1);
            this.textViewVersion = (TextView) itemView.findViewById(R.id.text2);
            this.imageViewIcon = (ImageView) itemView.findViewById(R.id.imageView);

            itemView.setOnClickListener(view -> {
                int pos = getAdapterPosition();

                if (onMovieDbClicked != null && pos != RecyclerView.NO_POSITION) {
                    MovieDb movieDb = dataSet.get(pos);
                    onMovieDbClicked.movieDbClicked(movieDb);
                }
            });
            //itemView.setOnClickListener(this);
            //itemView.setOnClickListener(CustomAdapter.myOnClickListener);
        }

        /*@Override
        public void onClick(View v) {
            int position = getAdapterPosition();
            mOnClickListener.onListItemClick(position);
        }*/
    }

    public CustomAdapter(List<MovieDb> data /*ListItemClickListener mOnClickListener*/) {
        this.dataSet = data;
        //this.mOnClickListener = mOnClickListener;
    }

    public interface OnMovieDbClicked {
        void movieDbClicked(MovieDb movieDb);
    }

    /*public interface ListItemClickListener{
        void onListItemClick(int position);
    }*/

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent,
                                           int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.cards_layout, parent, false);

        //view.setOnClickListener(FragmentOne.myOnClickListener);

        MyViewHolder myViewHolder = new MyViewHolder(view);
        return myViewHolder;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, final int listPosition) {

        TextView textViewName = holder.textViewName;
        TextView textViewVersion = holder.textViewVersion;
        ImageView imageView = holder.imageViewIcon;
        Glide.with(imageView).load("https://image.tmdb.org/t/p/w500" + dataSet.get(listPosition).getPosterPath()).into(imageView);

        textViewName.setText(dataSet.get(listPosition).getOriginalTitle());
        textViewVersion.setText(dataSet.get(listPosition).getReleaseDate());


    }


    @Override
    public int getItemCount() {
        if(dataSet == null){
            return 0;
        }
        return dataSet.size();
    }
}