c＃插入mySQL数据库时，textbox中的值变为默认值

Question

我正在创建一个Windows窗体应用程序，允许用户从MonthCalendar中选择值，然后将它们插入到数据库中。 我正在使用以下方法在文本框中显示日期。

     private void checkIn_DateChanged(object sender, DateRangeEventArgs e)
     {
        var monthCalendar = sender as MonthCalendar;
        txtcheckIn.Text = monthCalendar.SelectionStart.ToShortDateString();
     }

日期在文本框中正确显示，但我正在使用它们，当它们插入数据库时​​，它们将显示为默认值。 我正在使用以下内容插入值

    private void Insert()
    {
        using (var command = new SqlCommand("INSERT INTO Reservation (NumAdults,NumChildren,RoomType,CheckIn,Checkout) " +
                    "VALUES (@numAdults,@numChildren,@roomType,@checkIn,@checkout)"))
        {
            try
            {    
                command.Connection = connection;
                connection.Close();

                // Enters Reservation fields into the parameters of the SQL Query
                command.Parameters.AddWithValue("@numAdults", txtNumAdults.Text);
                command.Parameters.AddWithValue("@numChildren", txtNumChild.Text);
                command.Parameters.AddWithValue("@roomType", roomTypeBox.GetItemText(roomTypeBox.SelectedItem));
                command.Parameters.AddWithValue("@checkIn", txtcheckIn.Text);
                command.Parameters.AddWithValue("@checkout", txtcheckOut.Text);
                // Opens connection and checks if query affects Reservation table
                connection.Open();                    
                if (command.ExecuteNonQuery() > 0)
                {
                    // If the query was successful, alert user and display updated Client Table
                    MessageBox.Show("Reservation Record Successfully Inserted.");                       
                    connection.Close();
                    displayReservations();
                    resetReservationFields();
                }
                else
                {
                    // Insertion failed, show user message
                    MessageBox.Show("Record Insertion Failed.");
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error Inserting: No fields entered. \n" + ex);
            }
            finally
            {                  
                    connection.Close();            
            }

数据库中日期的格式是“datetime”，我不明白文本框中的日期会发生什么。