Get type of a class and instantiate another instance of it

Question

Question

I have a base class Number that is inherited by classes One , Two and Three .

I have a property

public Number SomeNumber{get;set;}

Initially, I have set SomeNumber to either One , Two or Three (Value Generated Randomly).

Later on, I want to set SomeNumber to a new class of the same type of the old class. Is this possible? If so, how?

Example:

On initialization, SomeNumber is set to One

Later on in the program, I want to set SomeNumber to a new instance of One .

Answer 1

I would add an abstract Method CreateInstance on the Number and implement it in all its concrete subclasses.

abstract class Number
{
  abstract Number CreateInstance();
}

class One : Number
{
  override Number CreateInstance()
  {
    return new One();
  }
}

"later on"

Number newNumber = SomeNumber.CreateInstance();

It doesn't need reflection, is therefore typesafe and it would support arguments if the constructors would need some.

Answer 2

SomeNumber = (Number)Activator.CreateInstance(SomeNumber.GetType());

For parameters, you must box up the parameters as such:

public partial class Form1 : Form
{
    public Number SomeNumber { get; set; }
    public Form1()
    {
        InitializeComponent();

        SomeNumber = new One();

        SomeNumber = (Number)Activator.CreateInstance(SomeNumber.GetType(), new[] {1});
    }

}

public class Number
{

}

public class One : Number
{
    public One()
    {

    }
    public One(Object a)
    {

    }

}

The post above by Stefan is a better method of implementing it. Another option would be to create an object factory