Question

我想在点击save按钮时更新一些信息。

我收到了错误

开：command.Parameters.Add（“@ doctorID”，SqlDbType.Int）.Value = resident.Doctor.DoctorID;说：对象引用未设置为对象的实例。

我猜我需要创建某种对象吗？

按键代码：

  private void btnSave_Click(object sender, RoutedEventArgs e)
    {
        Resident hello = new Resident();
        hello.Doctor = new Doctor();
        Resident residentID;

        txtAdditionalInformation.Text = hello.addtionalInformation;
        txtForename.Text = hello.FirstName;
        txtSurname.Text = hello.Surname;
        txtTitle.Text = hello.Title;



        ResidentData.Update(hello);
    }

更新代码（ResidentData Class）：

   public static void Update(Resident resident, SqlConnection connection,                  SqlTransaction transaction)
    {
        StringBuilder sqlString = new StringBuilder();
        SqlCommand command;

        sqlString.Append("UPDATE [Resident] SET ");
        sqlString.Append("title = @title, ");
        sqlString.Append("firstName = @firstName, ");
        sqlString.Append("surname = @surname, ");
        sqlString.Append("dateOfBirth = @dateOfBirth, ");
        sqlString.Append("photo = @photo, ");
        sqlString.Append("doctorID = @doctorID, ");
        sqlString.Append("roomID = @roomID, ");
        sqlString.Append("allergies = @allergies, ");
        sqlString.Append("additionalInformation = @additionalInformation ");
        sqlString.Append("WHERE residentID = @residentID ");
        command = new SqlCommand(sqlString.ToString(), connection);
        if ((transaction != null)) command.Transaction = transaction;

        command.Parameters.Add("@residentID", SqlDbType.Int).Value = resident.ResidentID;
        command.Parameters.Add("@title", SqlDbType.VarChar, 50).Value = Helper.GetValue(resident.Title);
        command.Parameters.Add("@firstName", SqlDbType.VarChar, 100).Value = Helper.GetValue(resident.FirstName);
        command.Parameters.Add("@surname", SqlDbType.VarChar, 100).Value = Helper.GetValue(resident.Surname);
        command.Parameters.Add("@dateOfBirth", SqlDbType.DateTime).Value = Helper.GetValue(resident.DateOfBirth);
        command.Parameters.Add("@photo", SqlDbType.Image, 2147483647).Value = Helper.GetValue(resident.Photo);
        command.Parameters.Add("@doctorID", SqlDbType.Int).Value = resident.Doctor.DoctorID;
        command.Parameters.Add("@roomID", SqlDbType.Int).Value = resident.Room.RoomID;
        command.Parameters.Add("@allergies", SqlDbType.NText).Value = resident.Allergies;
        command.Parameters.Add("@additionalInformation", SqlDbType.NText).Value = resident.addtionalInformation;
        int rowsAffected = command.ExecuteNonQuery();

        if (!(rowsAffected == 1))
        {
            throw new Exception("An error has occurred while updating Resident details.");
        }
    }

* 公寓类：

 {
    public class Resident
    {

    private int residentID;
    private string title;
    private string firstName;
    private string surname;
    private string searchText;
    private System.DateTime dateOfBirth;
    private byte[] photo;
    private Room room;
    private Doctor doctor;
    private string nhs;
    private string residentBarcode;
    private string allergies;
    private string additionalInformation;

    public Resident()
        : base()
    {
    }

    public Resident(int newResidentID, string newTitle, string newFirstName, string newSurname, string newSearchText, System.DateTime newDateOfBirth, byte[] newPhoto, Room newRoom, Doctor newDoctor, string newNhs, string newResidentBarcode, string newAllergies, string newAdditionalInformation)
        : base()
    {
        residentID = newResidentID;
        title = newTitle;
        firstName = newFirstName;
        surname = newSurname;
        searchText = newSearchText;
        dateOfBirth = newDateOfBirth;
        photo = newPhoto;
        room= newRoom;
        doctor = newDoctor;
        nhs = newNhs;
        residentBarcode = newResidentBarcode;
        allergies = newAllergies;
        additionalInformation = newAdditionalInformation;
    }

    public int ResidentID
    {
        get { return residentID; }
        set { residentID = value; }
    }

    public string Title
    {
        get { return title; }
        set { title = value; }
    }

    public string FirstName
    {
        get { return firstName; }
        set { firstName = value; }
    }

    public string Surname
    {
        get { return surname; }
        set { surname = value; }
    }

    public string SearchText
    {
        get { return searchText; }
        set { searchText = value; }
    }

    public System.DateTime DateOfBirth
    {
        get { return dateOfBirth; }
        set { dateOfBirth = value; }
    }

    public byte[] Photo
    {
        get { return photo; }
        set { photo = value; }
    }


    public Room Room
    {
        get { return room; }
        set { room = value; }
    }

    public Doctor Doctor
    {
        get { return doctor; }
        set { doctor = value; }
    }

    public string NHS
    {
        get { return nhs; }
        set { nhs = value; }
    }

    public string ResidentBarcode
    {
        get { return residentBarcode; }
        set { residentBarcode = value; }
    }

    public string Allergies
    {
        get { return allergies; }
        set { allergies = value; }
    }
    public string addtionalInformation{

        get { return additionalInformation; }
        set { additionalInformation = value; }

    } 


}

}

Answer 1

查看您创建Resident的方式：

Resident hello = new Resident();
ucMedicationCheckIn.SaveCheckedInMedication();
ResidentData.Update(hello);
ucMedicationCheckIn.HideDetails();

你可能还没有给它分配医生，这就是为什么它在这条线上失败的原因：

command.Parameters.Add("@doctorID", SqlDbType.Int).Value = resident.Doctor.DoctorID;

您需要初始化Doctor类型

编辑*

看到Resident课程后，我发现您还没有初始化Room。

您可以提供构造函数来将这些值初始化为默认值：

public Resident()
{
    this.Doctor = new Doctor();
    this.Room = new Room();
    //etc...   
}

虽然要做任何有意义的事情，但您可能希望在保存之前用实际数据设置它们。

Answer 2

这是因为您的Doctor和Room未在任何地方初始化：

Resident hello = new Resident();
hello.Doctor = new Doctor();
hello.Room = new Room();

但该更新可能会失败，因为resident中没有有意义的数据，rowsAffected可能会返回0。

添加参数时，对象引用未设置为对象的实例

2 个答案: