Object variables in C#

Question

Is there such a thing as an object variable in C#, and if it is, then how should users pass them on to functions as parameters?

Can users provide me some examples?

Regards,

JohnCTX

Answer 1

Since others have covered the basics I would add it's best to use strong type parameters rather than a base object. Then using a plain object you would then need to first check it's underlying type then cast it.

Below is the tip of the iceberg.

Example, I want a list of employees and managers in a list.

We start off with a base class person

public class Person : IPerson  
{  
    public int Id { get; set; }  
    public string FirstName { get; set; }  
    public string LastName { get; set; }  
    public DateTime HireDate { get; set; }  
    public string FullName => $"{FirstName} {LastName}";  
    public override string ToString() => $"{Id} {FullName}";  
}  

Employee class which inherits Person

public class Employee : Person  
{  
    public int ReportsTo { get; set; }  
}  

Mock them up into a single list

public class Mocked  
{  
    public static List<Person> PeopleList()  
    {  
        var employees = new List<Employee>()  
        {  
            new() {Id = 1, FirstName = "Joe", LastName = "Jones", HireDate = new DateTime(2018,12,1), ReportsTo = 5},  
            new() {Id = 2, FirstName = "Mary", LastName = "Smith", HireDate = new DateTime(2018,9,1), ReportsTo = 5},  
            new() {Id = 3, FirstName = "Nancy", LastName = "Ravioli", HireDate = new DateTime(2017,4,12), ReportsTo = 6},  
            new() {Id = 4, FirstName = "Andrew", LastName = "Fuller", HireDate = new DateTime(2019,7,2), ReportsTo = 6},  
            new() {Id = 7, FirstName = "Steven", LastName = "Buchanan", HireDate = new DateTime(2015,5,16), ReportsTo = 5},  
            new() {Id = 9, FirstName = "Karen", LastName = "Stone", HireDate = new DateTime(2020,5,16), ReportsTo = 8}  
        };  
  
        var people = new List<Person>()  
        {  
            new Manager() {Id = 5, FirstName = "Anne", LastName = "Wordsworth",   
                HireDate = new DateTime(2015,7,2), YearsAsManager = 3,Employees = employees.Take(2).ToList()},  
            new Manager() {Id = 6, FirstName = "Bob", LastName = "Gallagher",   
                HireDate = new DateTime(2014,7,2), YearsAsManager = 4,Employees = employees.Skip(2).Take(2).ToList()},  
            new Manager() {Id = 8, FirstName = "Michael", LastName = "Suyama",  
                HireDate = new DateTime(2014,7,2), YearsAsManager = 1,Employees = employees.Skip(employees.Count -1).Take(1).ToList()}  
        };  
  
        people.AddRange(employees);  
  
        return people;  
    }  
}  

Then say in a form declare a list of Person

private readonly List<Person> _peopleList;  

In form load event load the list using the mocked data above.

_peopleList = Mocked.PeopleList();  

Then check types

foreach (Person person1 in _peopleList)  
{  
    if (person1 is Manager person)  
    {  
        _stringBuilder.AppendLine(person.FullName);  
    }  
}  

Other ideas, use generics e.g.

namespace ExtensionsLibrary  
{  
    public static class GenericExtensions  
    {  
  
        public static bool IsPositive<T>(this T value) where T : struct, IComparable<T> =>  
            value.CompareTo(default(T)) > 0;  
  
    }  
}  

Usage on int a and decimal

decimal someDecimal = 1.4m;  
int someInt = 3;  
  
if (someDecimal.IsPositive())  
{  
      
}  
  
if (someInt.IsPositive())  
{  
      
}  

Then if all elements are the same why use object e.g. (where sampleArray might be passed as a parameter)

Type type = typeof(string);  
object[] sampleArray = { "Hello", "C#" };  
  
var destinationArray = Array.CreateInstance(type, sampleArray.Length);  
Array.Copy(sampleArray, destinationArray, sampleArray.Length);  

Look at param arrays.

Then finally pattern matching

foreach (var o in sampleArray)  
{  
    switch (o)  
    {  
        case string s:  
            Console.WriteLine($"o is a string with value of {s}");  
            break;  
        case int i:  
            Console.WriteLine($"o is a int with value of {i}");  
            break;  
        case bool b:  
            Console.WriteLine($"Bool {b}");  
            break;  
    }  
}  

Answer 2

There is an Object type you can use.

  object myObject = new object();

You can use it like so in a function parameter

    private bool MyFunction(object myInput)
    {

Keep in mind object is the base class for everything so you pass anything in as an object

Answer 3

You can see MSDN docs :
The object type
Boxing and Unboxing
...

Answer 4

Hi

 public void Userlogin()
        {
          cls_Users user=new cls_Users();
          user =  usercmd.GetByUsernameAndPassWord(txtUserName.Text, HelperClass.EncryptPassword(txtPassword.Text));
          if (user.UserName != null)
          {

            Hide();
            MDIToolbarForm frm = new MDIToolbarForm();
            frm.tSLUserName.Text = user.UserName.ToString();

            frm.Show();
          }

          else
          {
            count++;
            XtraMessageBox.Show(HelperClass.EncryptPassword(txtPassword.Text));
            XtraMessageBox.Show("تأكد من أسم المستخدم وكلمة المرور", "دخول", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            HelperClass.ClearValues(tableLayoutPanel2);
            txtUserName.Focus();
          }
          if (count == 3)
          {
            Application.Exit();
          }
  }

//See other code

 public static void StartOperation(Form frm)
        {
            frm.Cursor = Cursors.WaitCursor;
            frm.Enabled = false;
        }

Best Regards.
Please remember to mark the replies as answers if they help.

Answer 5

Everything in .NET, an OO language platform, derives form System.Object the base object for all objects.

https://learn.microsoft.com/en-us/dotnet/api/system.object?view=net-5.0

https://www.guru99.com/c-sharp-variables-operator.html

<copied>

A variable is a name given to a storage area that is used to store values of various data types. Each variable in C# needs to have a specific type, which determines the size and layout of the variable's memory.

<end>

https://www.tutorialsteacher.com/csharp/csharp-data-types

Primitive type string object has its System.String class as an example as does all .NET objects have a defined 'type' with 'type' being a class the blueprint that an object is derived from with System.Object being the base class/object for all .NET classes/objects.

https://learn.microsoft.com/en-us/dotnet/api/system.string?view=net-5.0

string strvariable = "help";

The you can use either Object or string to pass strvariable as a parm to a method() or to a class constructor.

private bool MyFunction(object obj)
{
string strvariable = (string) obj; 'you must cast the base object to the type
it contains.
}

private bool MyFunction(string strvariablepassed )
{

string strvariable = strvariablepassed 'the type is known "string"
}

It's OO 101 for OO language platforms .NET, Java or whatever else that uses OO.

https://alfredjava.wordpress.com/2008/07/08/class-vs-object-vs-instance/