将对象强制转换为接口会引发异常

Question

我正在尝试将一个类强制转换为接口。我得到了这个例外。

我试图观察所有使用过的元素，但似乎一切正常。

！[代码异常] https://i.imgur.com/twY6Bl2.png 我的IStocarePacienti接口代码是：

namespace DataAccess
{
    public interface IStocarePacienti : IStocareFactory
    {
        List<Pacient> GetPacienti();
        Pacient GetPacient(int id);
        bool AddPacient(Pacient d);

        bool UpdatePacient(Pacient d);
    }
}

对于我的班级：

namespace DataAccess
{
    public class AdministrarePacienti : IStocareFactory
    {
        private const int PRIMUL_TABEL = 0;
        private const int PRIMA_LINIE = 0;

        public List<Pacient> GetPacienti()
        {
            var result = new List<Pacient>();
            var dsCompanii = SqlDBHelper.ExecuteDataSet("select * from pacienti_ac", CommandType.Text);

            foreach (DataRow linieDB in dsCompanii.Tables[PRIMUL_TABEL].Rows)
            {
                result.Add(new Pacient(linieDB));
            }
            return result;
        }

        public Pacient GetPacient(int id)
        {
            Pacient result = null;
            var dsCompanii = SqlDBHelper.ExecuteDataSet("select * from pacienti_ac where ID_PACIENT = :ID_PACIENT", CommandType.Text,
                new OracleParameter(":ID_PACIENT", OracleDbType.Int32, id, ParameterDirection.Input));

            if (dsCompanii.Tables[PRIMUL_TABEL].Rows.Count > 0)
            {
                DataRow linieDB = dsCompanii.Tables[PRIMUL_TABEL].Rows[PRIMA_LINIE];
                result = new Pacient(linieDB);
            }
            return result;
        }

        public bool AddPacient(Pacient comp)
        {
            return SqlDBHelper.ExecuteNonQuery(
                "INSERT INTO pacienti_ac VALUES (seq_pacienti_ac.nextval, :NUME, :PRENUME, :TELEFON, :GR_SANGUINA, :CNP, :DATA_NASTERII)", CommandType.Text,
                new OracleParameter(":NUME", OracleDbType.NVarchar2, comp.Nume, ParameterDirection.Input),
                new OracleParameter(":PRENUME", OracleDbType.NVarchar2, comp.Prenume, ParameterDirection.Input),
                new OracleParameter(":TELEFON", OracleDbType.NVarchar2, comp.Telefon, ParameterDirection.Input),
                new OracleParameter(":GR_SANGUINA", OracleDbType.NVarchar2, comp.GrSanguina, ParameterDirection.Input),
                new OracleParameter(":CNP", OracleDbType.NVarchar2, comp.CNP, ParameterDirection.Input),
                new OracleParameter(":DATA_NASTERII", OracleDbType.Date, comp.DataNasterii, ParameterDirection.Input));
        }

        public bool UpdatePacient(Pacient comp)
        {
            return SqlDBHelper.ExecuteNonQuery(
                "UPDATE pacienti_ac set NUME = :NUME, PRENUME = :PRENUME, TELEFON = :TELEFON, GR_SANGUINA = :GR_SANGUINA, CNP = :CNP, DATA_NASTERII = :DATA_NASTERII where ID_PACIENT = :ID_PACIENT", CommandType.Text,
                new OracleParameter(":NUME", OracleDbType.NVarchar2, comp.Nume, ParameterDirection.Input),
                new OracleParameter(":PRENUME", OracleDbType.NVarchar2, comp.Prenume, ParameterDirection.Input),
                new OracleParameter(":TELEFON", OracleDbType.NVarchar2, comp.Telefon, ParameterDirection.Input),
                new OracleParameter(":GR_SANGUINA", OracleDbType.NVarchar2, comp.GrSanguina, ParameterDirection.Input),
                new OracleParameter(":CNP", OracleDbType.NVarchar2, comp.CNP, ParameterDirection.Input),
                new OracleParameter(":ID_PACIENT", OracleDbType.Int32, comp.IdPacient, ParameterDirection.Input));
        }
    }
}

我不知道该怎么办。正如我所说，一切对我来说都很好。