アンドロイドでデータベースにクエリを実行中にNULLポインタ例外が発生しましたか？

Question

data/data folderのテーブルをAndroidで作成しましたが、データベースから値をフェッチしようとしているうちに、null pointer Exceptionがコード内で指摘されています。databaseをチェックしましたが、カラムはアプリケーションから値を取得しています。 。あなたを行う

//some class  
//row_idealweight and row_goal are the name of column in the table table_name. 

    DietpointHelper db; 
    Cursor c=db.getReadableDatabase().query(db.table_name,new String[]{db.row_idealweight,db.row_goal}, null, null, null, null, null);<---NULL POINTER EXCEPTION 

    while(c.moveToNext()) 
     { 
     et_ideal.setText(c.getString(c.getColumnIndex(db.row_idealweight))); 
     et_goal.setText(c.getString(c.getColumnIndex(db.row_goal))) ; 
     } 
     db.close(); 

    //end of class.. 

    public class DietpointHelper extends SQLiteOpenHelper{ 
      /** Called when the activity is first created. */ 
      //creating db 
      private final static String db_name="Modify_Program"; 
      private final static int vs=1; 

      //creating columns 

      final String table_name="Modify_program"; 
      final String row_Primary="_id"; 
      final String row_Weight="col_weight"; 
      final String row_Gender="col_gender"; 
      final String row_Height="col_height"; 
      final String row_Birthday="col_birthdate"; 
      final String row_Current_Weight="col_currentWeight"; 
      final String row_goal="col_goal"; 
      final String row_idealweight="col_idealweight"; 

      //creating statement 
     String database_create= "CREATE TABLE "+table_name+"(" 
       +row_Primary+" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, " 
       + row_Weight + " TEXT, " 
       +row_Gender+" TEXT , " 
       +row_Height+" TEXT , " 
       +row_Birthday+" TEXT, " 
       +row_Current_Weight+" TEXT, " 
       +row_idealweight+" TEXT, " 
       +row_goal+" TEXT "+");" ; 


      public void addData(Record rec) 
      { 
       SQLiteDatabase db=this.getReadableDatabase(); 

       ContentValues values=new ContentValues(); 

       values.put(row_Weight,rec.getWeight()); 
       values.put(row_Gender, rec.getCheck()); 
       values.put(row_Height, rec.getHeight()); 
       values.put(row_Birthday, rec.getBday()); 
       values.put(row_Current_Weight, rec.getWeight()); 
       values.put(row_goal,rec.getGoal()); 
       values.put(row_idealweight,rec.getIdealWeight()); 
       values.put(row_Primary,1); 

        db.insert(table_name,row_Weight, values); 
       } 


      public DietpointHelper(Context context) 
        { 
        super(context, db_name, null,vs); 
        // TODO Auto-generated constructor stub 
       } 

      public void onCreate(SQLiteDatabase database) 
      { 

       database .execSQL(database_create); 

      } 

      @Override 
      public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
      { 
       // TODO Auto-generated method stub 
      db.execSQL("DROP TABLE IF EXISTS " +table_name); 
        onCreate(db); 
      }  

     }//class 

Answer 1

//use these in ur Activity  
    DataBaseAdapter dbAdapter = new DataBaseAdapter(this); 
       dbAdapter.open(); 

    Cursor cr = dbAdapter.Yourfetch_method Name(); 

       cr.moveToFirst(); 

     while (!cr.isAfterLast()) { 
       map = new HashMap<String, Object>(); 

       byte[] bytes = cr.getBlob(cr.getColumnIndex("Image")); 

       Bitmap bmp = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); 

       map.put("Image", bmp); 

       map = null;  

        cr.moveToNext(); 

       } 
    //create table by using following class DbHelper 

    public class DBHelper extends SQLiteOpenHelper { 
     private static final String DATABASE_NAME = "TryOnDB"; 

     private static final int DATABASE_VERSION =1; 

     // Database creation sql statement 

     public static final String tablename= "create table dbname(Image BLOB);"; 



     public DBHelper(Context context) { 
      super(context, DATABASE_NAME, null, DATABASE_VERSION); 
     } 

     // Method is called during creation of the database 
     @Override 
     public void onCreate(SQLiteDatabase database) { 
      database.execSQL(tablename); 

     } 

     // Method is called during an upgrade of the database, e.g. if you increase 
     // the database version 
     @Override 
     public void onUpgrade(SQLiteDatabase database, int oldVersion, 
       int newVersion) { 
      Log.w(DBHelper.class.getName(), 
        "Upgrading database from version " + oldVersion + " to " 
          + newVersion + ", which will destroy all old data"); 
      database.execSQL("DROP TABLE IF EXISTS FavoriteTable"); 

      onCreate(database); 
     } 


      public boolean deleteDatabase(Context context) { 
       return context.deleteDatabase(DATABASE_NAME); 
      } 




    } 

    //use DataBaseAdpter Class to fetchdata 

    public class DataBaseAdapter { 

     // Database fields 

     private Context context; 
     private SQLiteDatabase database; 
     private DBHelper dbHelper; 

     public DataBaseAdapter(Context context) { 
      this.context = context; 
     } 

     public DataBaseAdapter open() throws SQLException { 
      dbHelper = new DBHelper(context); 
      database = dbHelper.getWritableDatabase(); 
      return this; 
     } 

     public void close() { 
      dbHelper.close(); 
     } 


     public Cursor Yourfetch_method Name() { 
      return database.query("FavoriteData", new String[] {"Image"}, null, null, null, null, null); 
     } 


     public void deleteTable(String tablename){ 
      database.execSQL("drop table if exists "+tablename+';'); 
     } 
     public void createIndividualTable(String query){ 
      database.execSQL(query); 
     } 




     public void InsertPhotosData(FavoriteData photos) { 
      ContentValues values = new ContentValues(); 
      values.put("photo", photos.Image); 

      database.insert("PhotosData", null, values); 

     } 


     public ContentValues createContentValues(String category, String summary, 
       String description) { 
      ContentValues values = new ContentValues(); 

      return values; 
     } 
    }