如何选择并从sqlite返回值？

Question

我创建了数据库并将值插入到表中。现在我试图选择一个数据，但我得到以下错误：

我粘贴了我的整个SQLHelper类代码。请任何人都可以让我知道我在做什么错误？

public class DatabaseHelper extends SQLiteOpenHelper { 
    private static final int DATABASE_VERSION = 1; 

    // Database Name 
    private static final String DATABASE_NAME = "MyDB.db"; 

    // Table Names 
    private static final String TABLE_USERS = "Users"; 
    private static final String TABLE_SCORES = "Scores"; 
    private static final String TABLE_SYNCSTATUS = "SyncStatus"; 

    // Common column names 
    private static final String KEY_ID = "id"; 
    private static final String KEY_CREATED_AT = "created_at"; 

    // USERS Table - column names 
    private static final String KEY_USERID = "userID"; 
    private static final String KEY_USERNAME = "userName"; 
    private static final String KEY_USERPSWD = "userPswd"; 
    private static final String KEY_FIRSTNAME = "firstName"; 
    private static final String KEY_LASTNAME = "lastName"; 

    // SCORES Table - column names 
    private static final String KEY_USER_ID = "userID"; 
    private static final String KEY_GAME_ID = "gameID"; 
    private static final String KEY_SCORES = "scores"; 

    // SYNCSTATUS Table - column names 
    private static final String KEY_STATRDATE = "startDate"; 
    private static final String KEY_ENDDATE = "endDate"; 
    private static final String KEY_STATUS = "status"; 

    // Table Create Statements 
    // USERS table create statement 
    private static final String CREATE_TABLE_USERS = "CREATE TABLE IF NOT EXISTS " 
      + TABLE_USERS + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_USERID 
      + " TEXT," + KEY_USERNAME + " INTEGER," + KEY_USERPSWD + " TEXT," 
      + KEY_FIRSTNAME + " TEXT," + KEY_LASTNAME + " TEXT," 
      + KEY_CREATED_AT + " DATETIME" + ")"; 

    // Scores table create statement 
    private static final String CREATE_TABLE_SCORES = "CREATE TABLE IF NOT EXISTS " 
      + TABLE_SCORES + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_USER_ID 
      + " INTEGER," + KEY_GAME_ID + " INTEGER," + KEY_SCORES + " INTEGER," 
      + KEY_CREATED_AT + " DATETIME" + ")"; 

    // Sync table create statement 
    private static final String CREATE_TABLE_SYNCSTATUS = "CREATE TABLE IF NOT EXISTS " 
      + TABLE_SYNCSTATUS + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," 
      + KEY_STATRDATE + " DATETIME," + KEY_ENDDATE + " DATETIME," + KEY_STATUS + " INTEGER," 
      + KEY_CREATED_AT + " DATETIME" + ")"; 

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

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     // creating required tables 
     db.execSQL(CREATE_TABLE_USERS); 
     db.execSQL(CREATE_TABLE_SCORES); 
     db.execSQL(CREATE_TABLE_SYNCSTATUS); 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // on upgrade drop older tables 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_USERS); 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_SCORES); 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_SYNCSTATUS); 
     // create new tables 
     onCreate(db); 
    } 

    public int validateUserLogin(String uname, String pswd) 
    { 
     SQLiteDatabase db = this.getReadableDatabase(); 
     String[] whereArgs = new String[]{uname, pswd}; 

     String query = "SELECT "+KEY_USERID+" FROM "+TABLE_USERS+" WHERE "+KEY_USERNAME+" = ? AND "+KEY_USERPSWD+" = ?"; 
     try{ 
      Cursor cur= db.rawQuery(query, whereArgs); 
        //Boolean b = cur.moveToFirst(); 
        if (cur.moveToFirst() == true) 
        { 
         return cur.getInt(cur.getColumnIndex(KEY_USERID)); 
        } 
        else 
         return -1; 
     }catch(Exception e){ 
      return -1; 
     } 

    } 

    public void insertValues(UsersCredential uc){ 
     SQLiteDatabase db= this.getWritableDatabase(); 
     ContentValues cv=new ContentValues(); 
     cv.put(KEY_USERID, uc.getUserID()); 
     cv.put(KEY_USERNAME, uc.getUserName()); 
     cv.put(KEY_USERPSWD, uc.getUserPassword()); 
     cv.put(KEY_FIRSTNAME, uc.getUserFirstName()); 
     cv.put(KEY_LASTNAME, uc.getUserLastName()); 
     cv.put(KEY_CREATED_AT, getDateTime()); 
     db.insert(TABLE_USERS, null, cv); 
    } 

    public void deleteRecords() { 
     SQLiteDatabase db= this.getWritableDatabase(); 
     db.execSQL("delete from Users"); 
    } 

    private String getDateTime() { 
     SimpleDateFormat dateFormat = new SimpleDateFormat(
       "dd-MM-yyyy HH:mm:ss", Locale.getDefault()); 
     Date date = new Date(); 
     return dateFormat.format(date); 
    } 
} 

，我发现了异常的validateUserLogin(String uname, String pswd)方法，什么是错误的，我的代码？

Answer 1

您的查询不会返回任何数据。 您必须检查返回值moveToFirst然后才能尝试访问数据。