Question

使用房间持久性，当试图让数据库插入或在项目中选择时，出现错误：

空对象引用上的AppDataBase.getMovieDao（）'

与该过程相关的类如下：

AppDataBase类：

@Database(entities = {Movies.class}, version = 1)
public abstract class AppDataBase extends RoomDatabase {

    public static final String DB_NAME = "Movies";
    private static AppDataBase INSTANCE;

    public static AppDataBase getDataBase(Context context){
        if (INSTANCE == null){
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(),AppDataBase.class,DB_NAME).build();
        }
        return INSTANCE;
    }

    public abstract MovieDao getMovieDao();
}

道上课：

@Dao
public interface MovieDao {

    @Insert
    void insertAll(Movies movies);

    @Update
    void updateAll(Movies... notes);

    @Query("SELECT * FROM moviestb")
    List<Movies> getAll();

    @Delete
    void deleteAll(Movies... notes);

}

实体类：

@Entity(tableName = "moviestb")
public class Movies {

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "idmovie")
    private long id;

    @ColumnInfo(name = "titlemovie")
    private String titlemovie;
........
}

搜索注册：

public void loadFromDB(){
    db.getDataBase(view.getContext());
    if(db.getMovieDao().getAll().size() > 0){
        adapter.setResults(db.getMovieDao().getAll());
    }else{
        Toast.makeText(view.getContext(),"Não há filmes cadastrados",Toast.LENGTH_SHORT).show();
        view.getActivity().finish();
    }
}

插入：

public View.OnClickListener onSaveClick(final String plot, final String diretor, final String autor,
                                            final String nome, final String tipo, final String ano, final String ator, final String imdb) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View itemView) {
                db.getDataBase(view.getContext());
                Movies movies = new Movies(nome,plot,imdb,"",ator,ano,tipo,diretor,autor);
                new InsertAsyncTask(db).execute(movies);

            }
        };
    }

    private class InsertAsyncTask extends AsyncTask<Movies,Void,Void>{
        private AppDataBase db;
        public InsertAsyncTask(AppDataBase appDataBase) {
            db = appDataBase;
        }

        @Override
        protected Void doInBackground(Movies... params) {
            db.getMovieDao().insertAll(params[0]);
            return null;
        }
    }

全部搜索：

public void loadFromDB(){
    db.getDataBase(view.getContext());
    if(db.getMovieDao().getAll().size() > 0){
        adapter.setResults(db.getMovieDao().getAll());
    }else{
        Toast.makeText(view.getContext(),"Não há filmes cadastrados",Toast.LENGTH_SHORT).show();
        view.getActivity().finish();
    }
}

在获取数据库时发生崩溃，我做错了什么？谢谢！

Answer 1

显然，

db是null。您的问题没有显示您为其指定值的位置。

请注意，getDataBase()是一种static方法。也许你应该在某处发表db=AppDataBase.getDataBase()声明。

在尝试获取项目或插入时使用空间持久性返回null数据库

1 个答案: