cast the Parent object to Child object in C#

Question

Hi i want to cast the Parent object to Child object in C#

public class Parent
{
    public string FirstName {get; set;}
    public string LastName {get; set;         


        

Answer 1

If I understand your "I just want to fill them automatically" comment correctly, you want to create a new Child object that's populated with the values of the Parent, with default values for the new properties. Best way to do that is to create a constructor that copies the values:

public class Parent
{
   public string FirstName {get; set;}
    public string LastName {get; set;}
    public string City {get; set;}
}

public class Child : Parent
{
    public string PhoneNumber {get; set;}
    public string MobileNumber {get; set;}

    public Child (Parent parentToCopy)
    {
        this.FirstName = parentToCopy.FirstName;
        this.LastName = parentToCopy.LastName;
        this.City = parentToCopy.City;

        this.PhoneNumber = string.Empty; // Or any other default.
        this.MobileNumber = string.Empty;
    } 
}

Now you can use LINQ, like the answers above, to create a Child out of each Parent:

List<Child> lstChild = lstParent.Select(parent => new Child(parent)).ToList();

Note that this is very similar to @daryal's answer, but wraps the parent-to-child copying logic inside the constructor, rather than having it outside in the new Child() call.