Copying the contents of a base class from a derived class

Question

I currently have a derived class and a base class. How can I make the base class of the derived class equal to a base class that I have? Will a shallow copy work?

Answer 1

If I understand you correctly, this will work:

class Derived : Base
{
    // all the code you had above, plus this:

    public Derived(Base toCopy)
    {
        this.name = toCopy.name;
        this.address = toCopy.address;
    }
}

Derived d = new Derived(b);

Answer 2

You will have to manually copy the fields of the Base instance to the new Derived instance.

A common way of doing this is by offering a copy constructor:

public Derived(Base other)
{
    if (other == null) {
        throw new ArgumentNullException("other");
    }

    this.name = other.name;
    this.address = other.address;
}

---

One more note about your code:

private string field; 
public string Field { get; set; }

This does not make much sense (same for the other properties).

public string Field { get; set; } means that a private field will automatically be created by the compiler. Your field field will never be used at all.

Either just write public string Field { get; set; }, as the private field will be created automatically. Or declare the Field property in a way so that your private field will be used:

private string field;

public string Field {
    get {
        return field;
    }
    set {
        field = value;
    }
}

Answer 3

I realize that a couple of other answers may have touched on this solution, but I wanted to spell it out more completely.

The solution I found was to populate the base class, then pass that base class into the constructor of the derived class. The constructor of the derived class populates its fields based on the base class.

class Base
{
    private string name; 
    public string Name { get; set; }
    private string address; 
    public string Address { get; set; }
}

class Derived:Base
{
    Derived(Base toCopy)
    {
        this.Name = toCopy.Name;
        this.Address = toCopy.Address;
    }

    private string field; 
    public String field { get; set; }
}

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Base b = new Base();
            b.Address = "Iliff";
            b.Name = "somename"; 

            //You are now passing the base class into the constructor of the derived class.
            Derived d = new Derived(b);


        }
    }
}

Answer 4

Create a copy constructor for the base class, in doing so you'll also need to create a parameterless one as well as by adding the copy constructor the default constructor will no longer be generated by the compiler. Then in the derived class call the base class's copy constructor.

public class Base
{
    public int Name { get; set; }
    public string Address { get; set; }

    public Base()
    { }

    public Base(Base toCopy)
    {
        this.Name = toCopy.Name;
        this.Address = toCopy.Address;
    }
}

public class Derived : Base
{
    public String Field { get; set; }

    public Derived(Base toCopy)
        : base (toCopy)
    { }

    // if desired you'll need a parameterless constructor here too
    // so you can instantiate Derived w/o needing an instance of Base
    public Derived()
    { }
}