Develop Reference

Updating a Control Within a Currently Open Form

I am writing a C# Application where I can add various types of students - a normal student, or a academic society student, or a arts and culture society student. On the main form, I have 3 data grids (one lists academic students, one list arts and culture students, and the other lists the normal students). For the user to specify additional information about a student (should they be an academic society student, or an arts and culture student, or both), another form will open up asking the user to add additional Information.
After the information has been specified, I would like to take that information, and add it to the relevant data grid, in other words, update the data grid in the main form.
How I thought I would tackle this idea:
Create a method in the main form to add a new entry to the data grid
Save the main form object into a Form object
Have a method which will will add a new row of data into the form object mentioned in step 2
Update the currently open main form with the form object I had saved.
I tried doing the above, and I get the error:
Error 1 Inconsistent accessibility: parameter type 'ONT2000_Practical_05.AcademicSocieties' is less accessible than method 'ONT2000_Practical_05.Form1.addAcademicStudentRow(ONT2000_Practical_05.AcademicSocieties)' c:\users\okuhle\documents\visual studio 2013\Projects\ONT2000 Practical 05\ONT2000 Practical 05\Form1.cs 35 21 ONT2000 Practical 05
I have 3 classes - AcademicSocieties, ArtsAndCultureSociety and Student...both AcademicSocieties and ArtsAndCultureSociety inherit the Student class. Below is the code for the classes:
THE STUDENT CLASS:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ONT2000_Practical_05
{
public class Student
{
private String studentNumber;
private String studentName;
private String studentDegree;
public Student(string number, string name, string degree)
{
studentNumber = number;
studentName = name;
studentDegree = degree;
}
public String getStudentName()
{
return studentName;
}
public String getStudentNumber()
{
return studentNumber;
}
public String getStudentDegree()
{
return studentDegree;
}
}
}
THE ACADEMICSSOCIETY CLASS:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ONT2000_Practical_05
{
public class AcademicSocieties : Student
{
private String courseCode;
private String societyName;
public AcademicSocieties(String studentName, String studentNumber, String studentDegree, String courseCode, String societyName) : base(studentNumber, studentName, studentDegree)
{
this.courseCode = courseCode;
this.societyName = societyName;
}
public String getCourseCode()
{
return courseCode;
}
public String getSocietyName()
{
return societyName;
}
}
}
THE ARTSANDCULTURE SOCIETY CLASS
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ONT2000_Practical_05
{
class ArtsAndCultureSociety : Student
{
private int experienceLevel;
private int competitionWins;
private String societyName;
private Boolean colours;
public ArtsAndCultureSociety(int level, int wins, string societyName, String studentNumber, String studentName, String studentDegree) : base(studentNumber, studentName, studentDegree)
{
experienceLevel = level;
competitionWins = wins;
this.societyName = societyName;
}
}
}
THE MAIN FORM:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace ONT2000_Practical_05
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void academicSocietiesToolStripMenuItem_Click(object sender, EventArgs e)
{
}
private void degreeLabel_Click(object sender, EventArgs e)
{
}
private void exitApplicationToolStripMenuItem_Click(object sender, EventArgs e)
{
Environment.Exit(0);
}
public void addAcademicStudentRow(AcademicSocieties thisStudent) //This is where the Error Occurs
{
academicSocietiesDataGrid.Rows.Add(thisStudent.getStudentName(), thisStudent.getSocietyName(), thisStudent.getCourseCode());
}
private void addStudentButton_Click(object sender, EventArgs e)
{
String studentName = ProgramFunctions.validateTextBoxData(studentNameTextBox);
String studentNumber = ProgramFunctions.validateStudentNumber(studentNumberTextBox);
String studentDegree = ProgramFunctions.validateTextBoxData(degreeTextBox);
if (studentName.Equals(null) || studentNumber.Equals(null) || studentDegree.Equals(null) || studentDegree.Equals("null")) //Error 1 is on this line
{
ProgramFunctions.displayMessage("Data Integrity Error", "As a result of one or more fields failing data validation, this application will not continue processing data");
} else
{
if (artsAndCultureCheckBox.Checked && academicCheckBox.Checked)
{
Student newStudent = new Student(studentNumber, studentName, studentDegree);
StudentData.setCurrentStudent(newStudent);
ProgramFunctions.saveCurrentForm(this);
GeneralStudentSocietyForm generalForm = new GeneralStudentSocietyForm();
generalForm.Visible = true;
generalForm.Focus();
} else if (academicCheckBox.Checked)
{
Student newStudent = new Student(studentNumber, studentName, studentDegree);
StudentData.setCurrentStudent(newStudent);
ProgramFunctions.saveCurrentForm(this);
AcademicSocietyForm academics = new AcademicSocietyForm();
academics.Visible = true;
academics.Focus();
} else if (artsAndCultureCheckBox.Checked)
{
Student newStudent = new Student(studentNumber, studentName, studentDegree);
StudentData.setCurrentStudent(newStudent);
ProgramFunctions.saveCurrentForm(this);
ArtsAndCultureForm artsAndCulture = new ArtsAndCultureForm();
artsAndCulture.Visible = true;
artsAndCulture.Focus();
} else
{
Student newStudent = new Student(studentNumber, studentName, studentDegree);
StudentData.addNewStudent(newStudent);
ProgramFunctions.displayMessage("Student Added", "A New Student has successfully been added to the database. Click OK to continue");
studentDataDataGird.Rows.Add(newStudent.getStudentName(), newStudent.getStudentNumber(), newStudent.getStudentDegree());
}
}
}
private void Form1_Load(object sender, EventArgs e)
{
ProgramFunctions.addNewAcademicSociety("Accounting Society");
ProgramFunctions.addNewAcademicSociety("Law Student Society");
ProgramFunctions.addNewAcademicSociety("Science Student Society");
ProgramFunctions.addNewAcademicSociety("Information Technology Student Society");
ProgramFunctions.addNewAcademicSociety("Business Science Student Society");
ProgramFunctions.addNewArtsAndCultureSociety("Choir Society");
ProgramFunctions.addNewArtsAndCultureSociety("Hip Hop Society");
ProgramFunctions.addNewArtsAndCultureSociety("Anime Society");
ProgramFunctions.addNewArtsAndCultureSociety("The Hockey Society");
}
private void studentDataDataGird_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
}
public void academicSocietiesDataGrid_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
}
}
}
THE PROGRAMFUNCTIONS Class (This is where I am saving the Form Object):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace ONT2000_Practical_05
{
class ProgramFunctions
{
private static List<String> academicSocieties = new List<String>();
private static List<String> artsAndCultureSocieties = new List<String>();
private static Form1 formObject;
public static void saveCurrentForm(Form1 formData)
{
formObject = formData;
}
public static void academicStudentDataGridRow(AcademicSocieties newStudent)
{
formObject.addAcademicStudentRow(newStudent);
}
public static Form1 updateMainForm()
{
return formObject;
}
public static void addNewAcademicSociety(String societyName)
{
academicSocieties.Add(societyName);
}
public static void addNewArtsAndCultureSociety(String societyName)
{
artsAndCultureSocieties.Add(societyName);
}
public static void displayMessage(String title, String Message)
{
MessageBox.Show(Message, title);
}
public static String validateTextBoxData(TextBox thisTextBox)
{
if (thisTextBox.Text.Equals(null) || thisTextBox.Text.Equals("") || thisTextBox.Text.Equals(" "))
{
displayMessage("Empty Data Detected!", "You may not specify empty data for the student");
return null;
} else
{
thisTextBox.Text = thisTextBox.Text.Trim();
thisTextBox.Text = thisTextBox.Text.ToUpper();
return thisTextBox.Text;
}
}
public static String getSelectedItem(ComboBox thisComboBox)
{
return thisComboBox.SelectedItem.ToString();
}
public static int getArtsAndCultureCount()
{
return artsAndCultureSocieties.Count;
}
public static int getAcademicSocietyCount()
{
return academicSocieties.Count;
}
public static String getAcademicSociety(int index)
{
return academicSocieties[index];
}
public static String getArtsAndCultureSociety(int index)
{
return artsAndCultureSocieties[index];
}
public static String validateStudentNumber(TextBox studentNumberTextBox)
{
if (studentNumberTextBox.Text.Equals(null) || studentNumberTextBox.Text.Equals("") || studentNumberTextBox.Text.Equals(" "))
{
displayMessage("Empty Data Detected!", "You did not input any data...Please be sure you do specify some data");
return null;
} else
{
if (!studentNumberTextBox.Text.StartsWith("s"))
{
displayMessage("Invalid Student Number", "You have entered an invalid student number. Please be sure this student number follows the correct format. The student number must begin with a 's' character. ");
return null;
}
if (studentNumberTextBox.Text.Length != 10)
{
displayMessage("Invalid Student Number", "The student number specified may not be longer than 10 characters");
return null;
}
return studentNumberTextBox.Text;
}
}
}
}

change the access modifier of the class ProgramFunctions,ArtsAndCultureSociety to public.

Could it be you are missing the access modifier 'public' in some of your class definitions? If you don't add public before ArtsAndCultureSociety, it will be private.

Web User Control Collection data is not storing

I wanted to create a web control which has collection featured in the ASPX. I have code below which has a problem.
I seem to turn off and objects collection editor(collection stable).But I object design information Design Time at runtime what you can not get
when I turn off the project.So in a way the information will be saved during design is disappear.
When I open the project files in aspx file nor what. Designer.cs do not coincide in any record in the file.
I want to show in the picture below, this situation partially.
Based on the above, or as seen in the example in asp.net collection listing on sample collection can fix or waiting for your advice.
Here is code
//******************************************************Rol.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace SANNET.ToolBox.TemelRoller
{/*
[ControlBuilder(typeof(ListItemControlBuilder))]
[ParseChildren(true, "Text")]*/
[TypeConverter(typeof(ExpandableObjectConverter))]
public class Rol
{
private string rolAdi;
private AksiyonTuru aksiyonIcinKullan;
private EfektTuru iseYapilacak;
private string hataMesaji;
private IOzelEfekt ozelEfekt;
public String RolAdi { get { return rolAdi; } set { rolAdi = value; } }
public AksiyonTuru AksiyonIcinKullan { get { return aksiyonIcinKullan; } set { aksiyonIcinKullan = value; } }
public EfektTuru IseYapilacak { get { return iseYapilacak; } set { iseYapilacak = value; } }
public String HataMesaji { get { return hataMesaji; } set { hataMesaji = value; } }
public IOzelEfekt OzelEfekt { get { return ozelEfekt; } set { ozelEfekt = value; } }
public Rol()
{
RolAdi = "Hicbiri";
}
/*
public string GetAttribute(string key)
{
return (String)ViewState[key];
}
public void SetAttribute(string key, string value)
{
ViewState[key] = value;
}*/
}
}
//******************************************************RolListesi.cs
using SANNET.ToolBox.Yardimcilar;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Drawing.Design;
using System.Web.UI;
namespace SANNET.ToolBox.TemelRoller
{
//[TypeConverterAttribute(typeof(System.ComponentModel.ExpandableObjectConverter))]
[TypeConverterAttribute(typeof(System.ComponentModel.ExpandableObjectConverter))]
public class RolListesi : CollectionBase//ICollection<Rol>
{
private Collection<Rol> roller;
private Control parent;
public RolListesi(Control parent)
{
this.parent = parent;
parent.PreRender += parent_PreRender;
parent.Load += parent_PreRender;
roller = new Collection<Rol>();
}
void parent_PreRender(object sender, EventArgs e)
{
RolIslemleri.PreRenderIsle((Control)sender, this);
}
public Control Parent { get { return this.parent; } }
public Rol rolGetir(String rolAdi)
{
foreach (Rol r in roller) {
if (r.RolAdi.Equals(rolAdi))
return r;
}
return null;
}
public bool Contains(String rolAdi)
{
return rolGetir(rolAdi) != null;
}
public Rol this[int index]
{
get { return (Rol)roller[index]; }
}
public void Add(Rol emp)
{
roller.Add(emp);
}
public void Remove(Rol emp)
{
roller.Remove(emp);
}
}
}
//******************************************************RolCollectionEditor.cs
using System;
using System.Collections.Generic;
using System.ComponentModel.Design;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SANNET.ToolBox.TemelRoller
{
public class RolCollectionEditor : CollectionEditor
{
public RolCollectionEditor(Type type)
: base(type)
{
}
protected override string GetDisplayText(object value)
{
Rol item = new Rol();
item = (Rol)value;
return base.GetDisplayText(string.Format("{0}, {1}", item.RolAdi,
item.AksiyonIcinKullan));
}
}
}
//******************************************************SANButton.cs
using DevExpress.Web.ASPxEditors;
using SANNET.ToolBox.TemelRoller;
using System.ComponentModel;
using System.Web.UI;
namespace SANNET.ToolBox.Bilesenler
{
public class SANButton : ASPxButton, IRolSahibi
{
private RolListesi roller;
/* [Editor(typeof(System.ComponentModel.Design.CollectionEditor),
typeof(System.Drawing.Design.UITypeEditor))]*/
[Editor(typeof(RolCollectionEditor),
typeof(System.Drawing.Design.UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public RolListesi Roller { get {
if (roller == null)
{
roller = new RolListesi(this);
}
return roller; } }
}
}

The answer is
[PersistenceMode(PersistenceMode.InnerProperty)]
Here is sample usage
private Roller roller;
[Editor(typeof(RolCollectionEditor), typeof(System.Drawing.Design.UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
[PersistenceMode(PersistenceMode.InnerProperty)]
public Roller Roller
{
get
{
if (roller == null)
{
roller = new Roller();
} return roller;
}
}

how can I add items to my ListView

I keep getting this error and I know why but I need help figuring out how I can solve it. The only way I have been able to add my items it to make a new form but that seems silly.
It wont work if I make all my methods static =(
I keep getting,
"An object reference is required for the non-static field, method, or
property 'Handicap_Calculator.FormMain.listViewLog'
\Form1.cs 74 13 Handicap Calculator"
Here´s my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Handicap_Calculator
{
public partial class FormMain : Form
{
//FormAddScore FormAddNewScore = new FormAddScore();
public static bool addScoreIsShown = false;
public static FormAddScore _FormAddScore;
public static ListViewItem Item;
//public static List<string> ScoreInfo = new List<string>();
public FormMain()
{
InitializeComponent();
}
public void button1_Click(object sender, EventArgs e)
{
try
{
if (_FormAddScore == null || _FormAddScore.IsDisposed)
{
_FormAddScore = new FormAddScore();
}
_FormAddScore.Show();
if (_FormAddScore.WindowState == FormWindowState.Minimized)
{
_FormAddScore.WindowState = FormWindowState.Normal;
}
_FormAddScore.BringToFront();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
public static void AddScore()
{
int Round = 1;
DateTime date = _FormAddScore.date;
string course = _FormAddScore.course;
int holes = _FormAddScore.holes;
int score = _FormAddScore.score;
float courseRating = _FormAddScore.courseRating;
float slopeRating = _FormAddScore.slopeRating;
string[] ScoreInfo = new string[7];
ScoreInfo[0] = Round.ToString();
ScoreInfo[1] = date.ToString();
ScoreInfo[2] = course;
ScoreInfo[3] = holes.ToString();
ScoreInfo[4] = score.ToString();
ScoreInfo[5] = courseRating.ToString();
ScoreInfo[6] = slopeRating.ToString();
AddToList(ScoreInfo);
}
public static void AddToList(string[] ScoreInfo)
{
Item = new ListViewItem(ScoreInfo);
//listViewLog.Items.Add(Item);
}
}
}
Edit...
Here is the class im calling it from:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Handicap_Calculator
{
public partial class FormAddScore : Form
{
public DateTime date;
public string course;
public int holes;
public int score;
public float courseRating;
public float slopeRating;
public FormAddScore()
{
InitializeComponent();
}
private void FormAddScore_FormClosing(object sender, FormClosingEventArgs e)
{
FormMain.addScoreIsShown = false;
}
public void getscore()
{
try
{
date = dateTimePicker1.Value;
course = textBoxCourse.Text;
holes = Convert.ToInt16(textBoxHoles.Text);
score = Convert.ToInt16(textBoxScore.Text);
courseRating = Convert.ToSingle(textBoxCourseRating.Text);
slopeRating = Convert.ToSingle(textBoxSlopeRating.Text);
}
catch(Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private void button1_Click(object sender, EventArgs e)
{
getscore();
FormMain.AddScore();
}
}
}

The simple solution is to define your methods AddScore and AddToList as non-static.
public void AddScore()
{
//your code
}
public void AddToList(string[] ScoreInfo)
{
// your code
}
If you want to use static methods you should pass the instance of your Form to the method, on which you want to add items to the ListView.
public static void AddScore(FormMain mainForm)
{
//your code
AddToList(mainForm, ScoreInfo);
}
public static void AddToList(FormMain mainForm, string[] ScoreInfo)
{
// your code
}
Update:
According to your updated code the solution is to pass the instance of your FormMain to your FormAddScore when you create it. In FormAddScore you store the reference to the FormMain instance to call the methods on.
public partial class FormAddScore : Form
{
// your code
private FormMain _mainForm;
public FormAddScore(){
InitializeComponent();
}
public FormAddScore(FormMain mainForm) : this(){
_mainForm = mainForm;
}
In your FormMain when you create the instance of FormAddScore you should use the constructor that expects an instance of FormMain
_FormAddScore = new FormAddScore(this);
With this setup you can change your methods to non-static and you can call the methods of FormMain in your FormAddScore, by using the stored reference in variable _mainForm.
_mainForm.AddScore();

Noob Concern: Assigning a value to variable from new class object. C#

DinnerFun dinnerFun = new DinnerFun { PeepQty = (int)nudPeepQty.Value };
I am creating a new object of the DinnerFun class and trying to assign the value from the numeric up down object from the form to the int variable PeepQty.
When I go into debug mode, I can see that sure enough nudPeepQty has a numeric value, but it is never assigned to PeepQty, and my ending calculation always ends as 0.
As the problem might be something related to something I've done outside this line of code, I will add the rest of my project below:
DinnerParty.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace MonuEventPlanning
{
class DinnerFun
{
const int FoodCost = 25;
public int PeepQty;
decimal CostOfBeverage;
decimal CostOfDecorations;
decimal TotalCost;
public void CalcDrinks(bool HealthOption)
{
if (HealthOption)
{
CostOfBeverage = 5M;
}
else
{
CostOfBeverage = 20M;
}
}
public void CalcDecorations(bool FancyOption)
{
if (FancyOption)
{
CostOfDecorations = (PeepQty * 15M) + 50M;
}
else
{
CostOfDecorations = (PeepQty * 7.5M) + 30M;
}
}
public decimal CalcTotalCost(bool HealthyOption)
{
if (HealthyOption)
{
TotalCost = (CostOfDecorations + CostOfBeverage) * .95M;
return TotalCost;
}
else
{
TotalCost = (CostOfBeverage + CostOfDecorations) + (PeepQty*25M);
return TotalCost;
}
}
}
}
------------Form1.cs -------------
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace MonuEventPlanning
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void btnCalc_Click(object sender, EventArgs e)
{
DinnerFun dinnerFun = new DinnerFun { PeepQty = (int)nudPeepQty.Value };
dinnerFun.CalcDrinks(cbxHealthy.Checked);
dinnerFun.CalcDrinks(cbxFancy.Checked);
DisplayCost();
}
public void DisplayCost()
{
DinnerFun dinnerFun = new DinnerFun();
tbxDisplayCost.Text = dinnerFun.CalcTotalCost(cbxHealthy.Checked).ToString("c");
}
}
}

The issue is that you are creating another DinnerFun that is not the same as the first one. Naturally the DinnerFun object in DisplayCost will have zero for the property value. Perhaps you meant this...
private void btnCalc_Click(object sender, EventArgs e)
{
DinnerFun dinnerFun = new DinnerFun { PeepQty = (int)nudPeepQty.Value };
dinnerFun.CalcDrinks(cbxHealthy.Checked);
dinnerFun.CalcDrinks(cbxFancy.Checked);
DisplayCost(dinnerFun);
}
public void DisplayCost(DinnerFun dinnerFun)
{
tbxDisplayCost.Text = dinnerFun.CalcTotalCost(cbxHealthy.Checked).ToString("c");
}

C# The type or namespace name could not be found

I have a problem that has been driving me nuts.
I have 2 ASPX pages in which the parent use Server.Transfer() function. The parent is called Submit.aspx whereas child is called Review.aspx
In Submit.aspx.cs, I have:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class Contacts_Submit : BasePage
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Review_Click(object sender, EventArgs e)
{
Server.Transfer("Review.aspx", true);
}
/*
* Sequence of functions that will server as a Get functionality that will
* return the text inside each textbox.
* These information will be used by "Review.aspx" to validate the
* information given by the user before final submission takes place.
*/
public string GetFirstName { get { return FirstName.Text; } }
public string GetLastName { get { return LastName.Text; } }
public string GetAddress { get { return Address.Text; } }
public string GetCountry { get { return Country.SelectedValue; } }
public string GetProvince { get { return Province.SelectedValue; } }
public string GetCity { get { return City.Text; } }
public string GetZipCode { get { return ZipCode.Text; } }
public string GetWorkPhone { get { return WorkPhone.Text; } }
public string GetMobilePhone { get { return MobilePhone.Text; } }
public string GetFax { get { return Fax.Text; } }
public string GetEmail { get { return Email.Text; } }
public string GetCompany { get { return Company.Text; } }
public string GetWebsite { get { return Website.Text; } }
public string GetRelationship { get { return Relationship.SelectedValue; } }
}
Whereas on the Review.aspx.cs, I have:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web.Security;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class Contacts_Review : BasePage
{
protected void Page_Load(object sender, EventArgs e)
{
if(PreviousPage != null)
{
Contacts_Submit prevpage = PreviousPage as Contacts_Submit;
//FirstName.Text = PreviousPage.GetFirstName;
}
}
}
The problem is when I declare "Contacts_Submit prevpage = PreviousPage as Contacts_Submit". The system is giving me an error that says "The type or namespace name 'Contacts_Submit' could not be found (are you missing a using directive or an assembly reference?)".
I am a beginner in both ASP.NET and C#, can anyone help me with this? Thank you SOOO MUCH.

I think you just want
Contacts_Submit prevpage = PreviousPage as Contacts_Submit;
instead of
Contacts_Submit prevpage = PreviousPage as System.Data.DataSet Contacts_Submit;

Contacts_Submit is type of Page and not in any way related to Dataset, so your cast is invalid.
remove that and it should be fine