SQLiteOpenHelper 생성자가 호출되지 않습니다.

Question

SQLiteOpenHelper을 사용하여 응용 프로그램을 만듭니다. 이 클래스에 대한 객체를 만들면 생성자가 호출되지 않아 그 메소드를 사용할 때 NullPointerException이됩니다. 피드백을 바탕으로

06-15 11:46:11.880 29965-29980/aakaashjois.inventoryapp I/art: Background partial concurrent mark sweep GC freed 1717(388KB) AllocSpace objects, 0(0B) LOS objects, 39% free, 1579KB/2MB, paused 10.377ms total 30.998ms 
06-15 11:46:11.904 29965-29965/aakaashjois.inventoryapp I/ViewRootImpl: CPU Rendering VSync enable = true 
06-15 11:46:19.049 29965-29965/aakaashjois.inventoryapp D/AndroidRuntime: Shutting down VM 
06-15 11:46:19.051 29965-29965/aakaashjois.inventoryapp E/AndroidRuntime: FATAL EXCEPTION: main 
                      Process: aakaashjois.inventoryapp, PID: 29965 
                      java.lang.NullPointerException: Attempt to invoke virtual method 'void aakaashjois.inventoryapp.DatabaseHandler.addItem(aakaashjois.inventoryapp.Item)' on a null object reference 
                       at aakaashjois.inventoryapp.MainActivity$2.onClick(MainActivity.java:108) 
                       at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:157) 
                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                       at android.os.Looper.loop(Looper.java:135) 
                       at android.app.ActivityThread.main(ActivityThread.java:5254) 
                       at java.lang.reflect.Method.invoke(Native Method) 
                       at java.lang.reflect.Method.invoke(Method.java:372) 
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902) 
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:697) 
06-15 11:46:19.115 29965-29965/aakaashjois.inventoryapp I/Process: Sending signal. PID: 29965 SIG: 9 

: 나는 오류를 얻을 때 여기

public class MainActivity extends AppCompatActivity { 

    private List<Item> items; 
    private ItemsListAdapter adapter; 
    private DatabaseHandler handler; 

    @Override 
    public void onCreate(final Bundle savedInstanceState, final PersistableBundle persistentState) { 
    super.onCreate(savedInstanceState, persistentState); 
    setContentView(R.layout.activity_main); 
    items = new ArrayList<>(); 
    final View emptyView = getLayoutInflater().inflate(R.layout.list_item_empty, null, false); 
    addContentView(emptyView, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT)); 
    final ListView itemList = (ListView) findViewById(R.id.itemList); 
    handler = new DatabaseHandler(this); 
    items.addAll(handler.getItems()); 
    adapter = new ItemsListAdapter(items, getApplicationContext()); 
    if (itemList != null) { 
        itemList.setAdapter(adapter); 
        itemList.setEmptyView(emptyView); 
        itemList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
         @Override 
         public void onItemClick(final AdapterView<?> parent, final View view, final int position, final long id) { 
         } 
        }); 
       } 
      } 

      @Override 
      public boolean onCreateOptionsMenu(final Menu menu) { 
       getMenuInflater().inflate(R.menu.menu_main, menu); 
       return true; 
      } 

      @Override 
      public boolean onOptionsItemSelected(final MenuItem item) { 
       if (item.getItemId() == R.id.action_add_item) { 
        final View dialogView = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog_add_item, null); 
        final EditText addItemName = (EditText) dialogView.findViewById(R.id.addItemName); 
        final EditText addItemPrice = (EditText) dialogView.findViewById(R.id.addItemPrice); 
        final EditText addItemCount = (EditText) dialogView.findViewById(R.id.addItemCount); 
        final EditText addItemSold = (EditText) dialogView.findViewById(R.id.addItemSold); 
        final AlertDialog.Builder itemAdder = new AlertDialog.Builder(new ContextThemeWrapper(MainActivity.this, R.style.Dialog)); 
        itemAdder.setTitle("Add Item"); 
        itemAdder.setMessage("Enter details about the new item"); 
        itemAdder.setView(dialogView); 
        itemAdder.setPositiveButton("Add", new DialogInterface.OnClickListener() { 
         @Override 
         public void onClick(final DialogInterface dialog, final int which) { 
          final Item item = new Item(); 
          final String itemName = addItemName.getText().toString().trim(); 
          String itemPrice = addItemPrice.getText().toString().trim(); 
          String itemCount = addItemCount.getText().toString().trim(); 
          String itemSold = addItemSold.getText().toString().trim(); 

            item.setItemName(itemName); 
            item.setItemPrice(itemPrice); 
            item.setItemCount(itemCount); 
            item.setItemSold(itemSold); 

    //This is where I get the error 
    /*java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List aakaashjois.inventoryapp.DatabaseHandler.addItem(item)' on a null object reference */ 
            handler.addItem(item); 
            items.clear(); 
            items.addAll(handler.getItems()); 
            adapter.notifyDataSetChanged(); 
           } 
          } 

        }); 
        itemAdder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { 
         @Override 
         public void onClick(final DialogInterface dialog, final int which) { 
          dialog.dismiss(); 
         } 
        }); 
        itemAdder.create().show(); 
        return true; 
       } 
       return super.onOptionsItemSelected(item); 
      } 
     } 

내 로그입니다 :

class DatabaseHandler extends SQLiteOpenHelper { 

    private static final int DATABASE_VERSION = 2; 
    private static final String DATABASE_NAME = "INVENTORY_MANAGER"; 
    private static final String TABLE_NAME = "INVENTORY"; 
    private static final String KEY_ID = "id"; 
    private static final String KEY_ITEM_NAME = "name"; 
    private static final String KEY_ITEM_PRICE = "price"; 
    private static final String KEY_ITEM_COUNT = "count"; 
    private static final String KEY_ITEM_SOLD = "sold"; 

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


    @Override 
    public void onCreate(final SQLiteDatabase db) { 
     final String CREATE_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME 
       + "(" + KEY_ID + " INTEGER PRIMARY KEY, " 
       + KEY_ITEM_NAME + " TEXT, " 
       + KEY_ITEM_PRICE + " TEXT, " 
       + KEY_ITEM_COUNT + " TEXT, " 
       + KEY_ITEM_SOLD + " TEXT)"; 
     db.execSQL(CREATE_TABLE); 
    } 

    @Override 
    public void onUpgrade(final SQLiteDatabase db, final int oldVersion, final int newVersion) { 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); 
     onCreate(db); 
    } 

    void addItem(final Item item) { 
     final SQLiteDatabase db = this.getWritableDatabase(); 
     final ContentValues contentValues = new ContentValues(); 
     contentValues.put(KEY_ITEM_NAME, item.getItemName()); 
     contentValues.put(KEY_ITEM_PRICE, item.getItemPrice()); 
     contentValues.put(KEY_ITEM_COUNT, item.getItemCount()); 
     contentValues.put(KEY_ITEM_SOLD, item.getItemSold()); 
     long id = db.insert(TABLE_NAME, null, contentValues); 
     Log.i("LOG", "" + id); 
     db.close(); 
    } 

    List<Item> getItems() { 
     final List<Item> items = new ArrayList<>(); 
     final String SELECT_QUERY = "SELECT * FROM " + TABLE_NAME; 
     final SQLiteDatabase db = getReadableDatabase(); 
     final Cursor cursor = db.rawQuery(SELECT_QUERY, null); 
     if (cursor.moveToFirst()) { 
      do { 
       final Item item = new Item(); 
       item.setId(Integer.parseInt(cursor.getString(0))); 
       item.setItemName(cursor.getString(1)); 
       item.setItemPrice(cursor.getString(2)); 
       item.setItemCount(cursor.getString(3)); 
       item.setItemSold(cursor.getString(4)); 
      } while (cursor.moveToNext()); 
     } 
     cursor.close(); 
     return items; 
    } 
} 

이 내 주요 활동의 코드는 다음과 같습니다 여기 내 DatabaseHandler 클래스 받은, 나는 SQLiteOpenHelper 클래스를 제거하고 해당 클래스없이 SQLite 구문을 작성했습니다. 응용 프로그램은 이제 아무 문제없이 실행됩니다. 도와 주셔서 감사합니다!

Answer 1

DatabaseAdapter이라는 새 클래스를 만듭니다. 여기에 다음 코드를 추가합니다 :

public class DatabaseAdapter { 
    private static final int DATABASE_VERSION = 2; 
    private static final String DATABASE_NAME = "INVENTORY_MANAGER"; 
    private static final String TABLE_NAME = "INVENTORY"; 
    private static final String KEY_ID = "id"; 
    private static final String KEY_ITEM_NAME = "name"; 
    private static final String KEY_ITEM_PRICE = "price"; 
    private static final String KEY_ITEM_COUNT = "count"; 
    private static final String KEY_ITEM_SOLD = "sold"; 

    private Context context; 
    SQLiteDatabase database; 
    DatabaseHelper helper; 

    public DatabaseAdapter(Context context) { 
     this.context = context; 
    this.helper = new DatabaseHelper(context); 
    } 

    private static class DatabaseHelper extends SQLiteOpenHelper { 
     DatabaseHelper(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
     public void onCreate(SQLiteDatabase db) { 
     try { 
      db.execSQL("CREATE TABLE IF NOT EXISTS " + TABLE_NAME 
        + "(" + KEY_ID + " INTEGER PRIMARY KEY, " 
        + KEY_ITEM_NAME + " TEXT, " 
        + KEY_ITEM_PRICE + " TEXT, " 
        + KEY_ITEM_COUNT + " TEXT, " 
        + KEY_ITEM_SOLD + " TEXT)"); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
      } 
     } 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      Log.w("Database", “Upgrading database from version “ +  oldVersion + “ to “ + newVersion + “, which will destroy all old data”); 
      db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); 
      onCreate(db); 
     } 
    } 

    public DatabaseAdapter open() throws SQLException { 
     this.database = DBHelper.getWritableDatabase(); 
     return this; 
    } 

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

    public long addItem(final Item item) { 
     ContentValues contentValues = new ContentValues(); 

     contentValues.put(KEY_ITEM_NAME, item.getItemName()); 
     contentValues.put(KEY_ITEM_PRICE, item.getItemPrice()); 
     contentValues.put(KEY_ITEM_COUNT, item.getItemCount()); 
     contentValues.put(KEY_ITEM_SOLD, item.getItemSold()); 

     return database.insert(TABLE_NAME, null, contentValues); 
    } 

    // Add the rest of your code here 
} 

을 주요 활동으로, 당신은 지금 너무로 DatabaseAdapter 클래스를 참조 할 수 있습니다 :

DatabaseAdapter database = new DatabaseAdapter(this); 
database.open(); 

// call any of the functions that you need 
long insert = database.addItem(Item parametre); 

database.close(); 

을 또한, etire 섹션에있다 this 전자 도서를 보라 SQLite 데이터베이스. 이렇게하면 문제가 해결 될 수도 있습니다.