java需要帮助使用安卓实现收藏夹吗？

Question

我正在开发一个应用程序，需要使用ROOM ORM实现收藏夹。我在一个片段中有不同的Dua，有一个按钮用于将该Dua插入数据库。插入部分工作正常，但当我试图通过单击我最近添加到收藏夹中的Dua来加载Dua时，会引发空指针异常，仅当我在同时。代码附在后面，下面是DAO类

import 安卓.arch.lifecycle.LiveData;
import 安卓.arch.persistence.room.Dao;
import 安卓.arch.persistence.room.Insert;
import 安卓.arch.persistence.room.Query;

import com.islam.cheapapps.dua101.model.Favorite;

import java.util.List;

/**
* Created by home on 16/06/2018.
*/
@Dao
public interface FavoriteDao {

@Insert
void insert(Favorite favorite);

@Query("DELETE FROM favorite_dua")
void deleteAll();

//ORDER BY word ASC if ordering is necessary.(optional)
@Query("SELECT * from favorite_dua")
LiveData<List<Favorite>> getAllDuas();

@Query("SELECT * FROM favorite_dua WHERE position = :position AND dua_category = :dua_category")
Favorite getFavoritePosition(int position, String dua_category);
}

类，其中单击了收藏夹按钮

public class ScreenSlidePageFragment extends Fragment {

JSONArray jsonArray;
FavoriteViewModel mWordViewModel;
// Variable for identification of category (0 for duas after salah, 1 for morning azkar) and so on
int id = 0;
private int pos = 0;
//Title Text View
private TextView headerTV;
//Pronunciation Text View
private TextView pronunciationTV;
//Translation Text View
private TextView translationTV;
//Benefit Text View
private TextView benefitTV;
//Reference Text View
private TextView referenceTV;
//Dua Image View
private ImageView duaIV;
//Favorite Button
private LikeButton favoriteBtn;
//Share Button
private SparkButton shareButton;


public void setPosition(int pos) {
    this.pos = pos;
}

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


    //Get reference to the dua title
    headerTV = rootView.findViewById(R.id.title);

    //Get reference to the dua pronunciation
    pronunciationTV = rootView.findViewById(R.id.pronounciationTV);

    //Get reference to the dua translation
    translationTV = rootView.findViewById(R.id.translationTV);

    //Get reference to the dua benefit
    benefitTV = rootView.findViewById(R.id.benefitTV);

    //Get reference to the dua reference
    referenceTV = rootView.findViewById(R.id.referenceTV);


    //Get reference to the dua img
    duaIV = rootView.findViewById(R.id.duaIV);


    //Get reference to the favorite Button
    favoriteBtn = rootView.findViewById(R.id.favorite_btn);

    //Get reference to the share Button
    shareButton = rootView.findViewById(R.id.share_btn);


    //Setting onClick Listener on share Button
    shareButton.setEventListener(new SparkEventListener() {
        @Override
        public void onEvent(ImageView imageView, boolean b) {

        }

        @Override
        public void onEventAnimationEnd(ImageView imageView, boolean b) {

        }

        @Override
        public void onEventAnimationStart(ImageView imageView, boolean b) {
            shareDua();
        }
    });
    //Setting onClick listener on the fav button which will add the dua to favorite list.
    favoriteBtn.setOnLikeListener(new OnLikeListener() {
        @Override
        public void liked(LikeButton likeButton) {
            addToFavorites();
        }

        @Override
        public void unLiked(LikeButton likeButton) {

        }
    });


    // Function for getting data of a specific category
    getData();
    // Function for setting data into the view
    setData();

    mWordViewModel = ViewModelProviders.of(this).get(FavoriteViewModel.class);
    return rootView;
}


// Getting Data for a specific category
private void getData() {

    id = getActivity().getIntent().getIntExtra("position", 0);

    switch (id) {
        case 0:
            readData(this.getResources().openRawResource(R.raw.c0));
            break;
        case 1:
            readData(this.getResources().openRawResource(R.raw.c1));
            break;
        case 2:
            readData(this.getResources().openRawResource(R.raw.c2));
            break;
        case 3:
            readData(this.getResources().openRawResource(R.raw.c0));
            break;
        case 4:
            readData(this.getResources().openRawResource(R.raw.c0));
            break;
        case 5:
            readData(this.getResources().openRawResource(R.raw.c0));
            break;
        default:
            break;
    }

}

/**
 * Reading data from the JSON array
 */
private void readData(InputStream in) {
    StringBuilder text = new StringBuilder();
    BufferedReader br = null;

    try {
        br = new BufferedReader((new InputStreamReader(in)));
        String line;
        while ((line = br.readLine()) != null) {
            text.append(line);
            text.append('\n');
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (br != null) {
                br.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    try {
        jsonArray = new JSONArray(text.toString());
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

/**
 * Set Data depending upon the position of view pager
 */
private void setData() {
    try {
        JSONArray tempJson = jsonArray.getJSONArray(this.pos);
        duaIV.setImageResource(getResources().getIdentifier(tempJson.getString(3).trim().substring(0, tempJson.getString(3).indexOf(".png")), "drawable", getActivity().getPackageName()));
        headerTV.setText(tempJson.getString(0).trim());
        pronunciationTV.setText(tempJson.getString(3).trim());
        translationTV.setText(tempJson.getString(9).trim());
        benefitTV.setText(tempJson.getString(12).trim());
        referenceTV.setText(tempJson.getString(11).trim());
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

/**
 * A share intent is fired and gives choice to user for sharing the current dua using the applications
 * that are present in his mobile
 */
private void shareDua() {
    /*try {
        sharingText = mJsonArray.getJSONObject(currPos).getString("seq") + "\n" +
                mJsonArray.getJSONObject(currPos).getString("narator") + "\n" +
                mJsonArray.getJSONObject(currPos).getString("hadith");
    } catch (JSONException e) {
        e.printStackTrace();
    }*/
    Intent sharingIntent = new Intent();
    sharingIntent.setAction(Intent.ACTION_SEND);
    sharingIntent.setType("text/plain");

    // sharingIntent.putExtra(Intent.EXTRA_TEXT, sharingText);

    startActivity(Intent.createChooser(sharingIntent, "Share using"));
}

//Add dua to favorite on pressing the favorite button
private void addToFavorites() {
    String dua_category = "";
    switch (id) {
        case 0:
            dua_category = "Duas after Salah";
            break;
        case 1:
            dua_category = "Morning Azkar";
            break;
        case 2:
            dua_category = "Evening Azkar";
            break;
        case 3:
            dua_category = "Rabbana Duas";
            break;
        case 4:
            dua_category = "Essential Duas";
            break;
        case 5:
            dua_category = "Ruquiya";
            break;
        default:
            dua_category = "";
            break;
    }

    Favorite favorite = new Favorite(headerTV.getText().toString(),
            pronunciationTV.getText().toString(), dua_category, this.pos);
    Toast.makeText(this.getContext().getApplicationContext(), "Position : " + this.pos + "Category : "
                    + dua_category
            , Toast.LENGTH_SHORT).show();
    mWordViewModel.insert(favorite);

}


}

在该类中，当项目已添加到列表中时，将实现对收藏夹项目的ONCLICK

public class FavoriteAdapter extends 
RecyclerView.Adapter<FavoriteAdapter.MyViewHolder> {
private final LayoutInflater mInflater;
private Context mContext;
private List<Favorite> mDuas; // Cached copy of words
String cat = "";

public FavoriteAdapter(Context mContext) {
    this.mContext = mContext;
    mInflater = LayoutInflater.from(mContext);
}

@Override
public FavoriteAdapter.MyViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
    View itemView = mInflater.inflate(R.layout.favorite_single_item, viewGroup, false);
    return new MyViewHolder(itemView);
}

@Override
public void onBindViewHolder(FavoriteAdapter.MyViewHolder holder, int position) {
    // Variable for holding the position of the current view that was clicked
    final int temp = position;

    if (mDuas != null) {
        Favorite current = mDuas.get(position);
        holder.favoriteHeader.setText(current.getHeader());
        holder.favoritePronunciation.setText(current.getDua_pronunciation());
        cat = current.getDua_category();
    } else {
        // Covers the case of data not being ready yet.
        holder.favoriteHeader.setText("No Word");
    }


    holder.favoriteCV.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {


            new Thread(new Runnable() {
                @Override
                public void run() {
                    FavoriteRoomDatabase db = FavoriteRoomDatabase.getDatabase(mContext);
                    FavoriteDao mFavoriteDao = db.favoriteDao();
                    Favorite f = mFavoriteDao.getFavoritePosition(temp, cat);
                    ////////////////////////// TEST LOGIC //////////////////////////////
                    Intent intent = new Intent(mContext, ScreenSlidePagerActivity.class);
                    intent.putExtra("fav", "favorite");
                    intent.putExtra("category", f.getDua_category());
                    intent.putExtra("position", f.getPosition());
                    mContext.startActivity(intent);
                    ////////////////////////////////////////////////////////////////////
                }
            }).start();
        }
    });

}

public void setDuas(List<Favorite> duas) {
    mDuas = duas;
    notifyDataSetChanged();
}


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

}

public class MyViewHolder extends RecyclerView.ViewHolder {
    public TextView favoriteHeader, favoritePronunciation;
    public ImageView favoriteImage;
    public CardView favoriteCV;

    public MyViewHolder(View itemView) {
        super(itemView);

        favoriteCV = itemView.findViewById(R.id.favoriteCV);
        favoriteHeader = itemView.findViewById(R.id.favorite_header);
        favoritePronunciation = itemView.findViewById(R.id.favorite_pronunciation);
        favoriteImage = itemView.findViewById(R.id.favorite_image);
    }
}
}