Question

I have this list of custom class objects:

List<URL> URLs = new List<URL>();

and I’m trying to push a copy on to a Stack:

Stack<List<URL>> undo = new Stack<List<URL>>();

List<URL> temp = new List<URL>();
temp.AddRange(new List<URL>(URLs));
undo.Push(temp);

Now whenever I delete an object from the original (URLs) list everything is OK with the one on the stack (temp). But when I delete a list element from a list inside the object in the original (URLs) the same element dissapears in the copy of that object’s list that is on the stack.

I delete objects from URLs the same way I delete list elements inside that object.
Does anyone know why this is happening?

Answer 1

That’s because List is basically an array i.e. a reference type. They will only have reference of each other.

make a Deep Copy using extension method

public static class ExtensionMethod
{  
    public static T DeepClone<T>(this T element)
    { 
        MemoryStream m = new MemoryStream();
        BinaryFormatter b = new BinaryFormatter();
        b.Serialize(m, element);
        m.Position = 0;
        return (T)b.Deserialize(m);
    }
}

and make sure that u declare your URL Class like this

[Serializable]
public class URL
{
   //..... Your Class
}

and call it like

temp.AddRange(URLs.DeepClone().ToList());