android sqliteデータベースに要素があるかどうかを確認

	private boolean search_city(String str) {

		CityDBHelper dbHelper = new CityDBHelper(MainActivity.this,
				"city_db_2", null, 1);
		SQLiteDatabase db = dbHelper.getWritableDatabase();

		Cursor cursor = db.rawQuery(
				"select * from   city_table  where   city=? ",
				new String[] { str });
		while (cursor.moveToNext()) {
			db.close();
			Log.i(" search_city_name_exist", str + "       ,return true");
			return true;// //          ，  true
		}
		db.close();
		Log.i(" search_city_name_exist", str + "       ，return false");
		return false;// //         false

	}

   ，      

<img src="http://img.blog.csdn.net/20151203000731879" alt="" />