android检查sqlite数据库中是否存在某个元素

	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 + "在数据库已存在,return true");
			return true;// //有城市在数据库已存在，返回true
		}
		db.close();
		Log.i(" search_city_name_exist", str + "在数据库不存在，return false");
		return false;// //在数据库以前存在 false

	}

经测试，是正确可靠的

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