Android 如何在rawQuery的whererg字段中使用字符串变量？

使用此代码时，我得到了正确的输出：

c=sdb.rawQuery("select * from " +  TABLE_ShopDetails + " where " + COL_UN + "=?  and " + COL_PWD + "=? " , new String[]{"pavan@demart","pavandemart"}); 

但当我使用：

 c=sdb.rawQuery("select * from " +  TABLE_ShopDetails + " where " + COL_UN + "=?  and " + COL_PWD + "=? " , new String[]{un,pwd});

我没有得到预期的结果。谁能告诉我在rawQuery的where子句中使用字符串变量的正确方法吗。我只想使用字符串变量而不是字符串文本

提前谢谢

    public class DatabaseHelper extends SQLiteOpenHelper {
        private static final String TAG=DatabaseHelper.class.getSimpleName();

        // Logcat tag
        private static final String LOG = "DatabaseHelper";


        // Database Version
        private static final int DATABASE_VERSION = 2;

        // Database Name
        private static final String DATABASE_NAME = "ShopDatabase";

        // Table Names
        private static final String TABLE_Products = "Products";
        private static final String TABLE_ShopDetails = "ShopDetails";
        private static final String TABLE_Feesdback = "Feesdback";


        //Products column names
        private static final String COL_PN = "ProductName";
        private static final String COL_PT = "ProductType";
        private static final String COL_COMP = "Company";
        private static final String COL_PR = "Price";
        private static final String COL_QT = "Quantity";

        // ShopDetails Table - column nmaes
        private static final String COL_SN = "ShopName";
        private static final String COL_SKN = "ShopkeeperName";
        private static final String COL_SA = "Address";
        private static final String COL_UN = "Username";
        private static final String COL_PWD = "Password";

        //Feesdback table column names
        private static final String COL_FPN = "PName";
        private static final String COL_FB = "Feesdback";


        // Table Create Statements
        // Todo table create statement
       private static final String CREATE_TABLE_PRODUCTS = " CREATE TABLE "
                + TABLE_Products + " ( " + COL_PN + " TEXT PRIMARY KEY, " + COL_PT + " TEXT, " + COL_COMP + " TEXT, " + COL_PR + " REAL, " +COL_QT+ " INTEGER " + " ) ";



        // Tag table create statement
        private static final String CREATE_TABLE_SHOPDETAILS = " CREATE TABLE "
                + TABLE_ShopDetails + " ( " + COL_SN + " TEXT PRIMARY KEY, " + COL_SKN + " TEXT, " + COL_SA + " TEXT, " + COL_UN + " TEXT, " +COL_PWD+ " TEXT " + " ) ";

        private static final String CREATE_TABLE_FEEDBACK = " CREATE TABLE "
                + TABLE_Feesdback + " ( " +COL_FPN + " TEXT PRIMARY KEY, " + COL_FB + " TEXT " + " ) ";

        private static Context context;

        public static SQLiteDatabase sdb;

           Cursor c;

             String username,password;

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



       //TODO Auto-generated constructor stub





        @Override
        public void onCreate(SQLiteDatabase sdb) {

            // creating required tables
            sdb.execSQL(CREATE_TABLE_PRODUCTS);


            sdb.execSQL(CREATE_TABLE_SHOPDETAILS);
            sdb.execSQL(CREATE_TABLE_FEEDBACK);

            sdb.execSQL("insert into " + TABLE_Products + " values('Rice','Grocery','Balaji',70.00,30)");
            sdb.execSQL("insert into " + TABLE_Products + " values('Oil','Grocery','SunFlower',45.00,20)");
            sdb.execSQL("insert into " + TABLE_Products + " values('Gelgyme','Laundry','Amway',600.00,20)");
            sdb.execSQL("insert into " + TABLE_ShopDetails + " values('Demart','Pavan','Malakpet','pavan@demart','pavandemart')");
            sdb.execSQL("insert into " + TABLE_ShopDetails + " values('More','Ragavendra','Kothapet','ragavendra@more','ragavendramore')");

            System.out.println("in oncreate");
        }

        @Override
        public void onUpgrade(SQLiteDatabase sdb, int oldVersion, int newVersion) {
            // on upgrade drop older tables
            sdb.execSQL("DROP TABLE IF EXISTS" + TABLE_Products);
            sdb.execSQL("DROP TABLE IF EXISTS" + TABLE_ShopDetails);

            // create new tables
            onCreate(sdb);
        }

       public void open()
       {
            sdb=this.getWritableDatabase();
       }

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


        public int validate(String un,String pwd)
        {
            sdb=this.getReadableDatabase();
         System.out.println("in validate method");

            username=un;
            password=pwd;
            System.out.println(username);
            System.out.println(password);
             int flag=0;
            Log.d(TAG, un);
            Log.d(TAG, pwd);

            //String[] qry={"pavan@demart","pavandemart"};
            System.out.println("in validate strings" + un + "," + pwd);
        //worked
            c=sdb.rawQuery("select * from " +  TABLE_ShopDetails + " where " + COL_UN + "=?  and " + COL_PWD + "=? " , new String[]{un,pwd});
         //c=sdb.rawQuery(" select * from " +  TABLE_ShopDetails + " where " + COL_UN + "= '" +  username + "' and " + COL_PWD + "= '" + password + "' ", null);
        //c=sdb.query(TABLE_ShopDetails, null, "Username=? and Password=?", qry, null, null, null);


            System.out.println("before while in try");
            if(c!=null)
            {
       if(c.moveToNext())
       {
           System.out.println("in while ");
                flag=1;
           }
            }
            else
                    System.out.println("c is null");
            c.close();
            sdb.close();
            return flag;
            }


    }

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考虑以下示例作为修复代码的参考，我认为问题在于传递给rawQuery的参数的字符串数组

  public Cursor getTrailByType(String id) {
     String[] args={id};

     return(getReadableDatabase()
          rawQuery("SELECT _id, NAME FROM trail WHERE TYPE_id=? OR ENT=?",
                args));
  }

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考虑到您使用的参数是正确的，错误在别处；并将qry变量传递给whererg字段。但我仍然无法解决该错误。