Reflection

How to make sure that any objects added to the Children property, gets a correct reference to the parent object (this)?

Attempt 1: Adding Add and Insert methods to the Element

public abstract class Element {
public Element() {
this.Children = new List<Element>();
}
public int ID { get; protected set; }
public string Name { get; protected set; }
public virtual Element Parent { get; internal set; }
public virtual List<Element> Children { get; private set; }
public string Instructions { get; set; }

public void Add(Element item){
item.Parent = this;
this.Children.Add(item);
}
...
}

This solution works all-right for many cases, however, it doesn't solve the issue when the Add method is used on the List<Element> directly. We'll want this.

Attempt 2: Changing the List type

public abstract class Element {
public Element() {
this.Children = new ElementList();
}
public int ID { get; protected set; }
public string Name { get; protected set; }
public virtual Element Parent { get; internal set; }
public virtual ElementList Children { get; private set; }
public string Instructions { get; set; }
}

public class ElementList : List<Element> {
public Element Element { get; internal set; }
public ElementList(Element element) {
if (element != null){ this.Element = element; }
else { throw new ArgumentNullException("element"); }
}
new public void Add(Element item) {
if ( item.Parent == null) { item.Parent = Element; }
base.Add(item);
}
new public void Insert(int index, Element item) {
if (item.Parent == null) { item.Parent = Element; }
base.Insert(index, item);
}
new public void InsertRange(int index, IEnumerable<Element> collection){
foreach (Element e in collection){
if (e.Parent == null) { e.Parent = Element; }
}
base.InsertRange(index, collection);
}
new public void AddRange(IEnumerable<Element> collection) {
foreach (Element e in collection) {
if (e.Parent == null) { e.Parent = Element; }
}
base.AddRange(collection);
}
}

This solution ensures that all Elements added to an ElementList, gets their Parent property re-set to reference the ElementLists Element property. This way, one can always assume that an Element's Children, always have their Parent references set.

Next up: Serialization.

Ok, so here's the scenario. I have a set of objects, which all inherit from Element (shown below). I need these objects to behave properly when transferred across a web service, and more importantly, when they return. One assumption I want to be able to make, is that any Element contained in the Children property, should have its Parent property set to the containing object, so it's a node-like structure. Furthermore, I need my non-default constructor logic to apply, to de-serialized objects, as if they were initialized with my parameterized constructor.

public abstract class Element {
public Element() {
this.Children = new List<Element>();
}
public int ID { get; protected set; }
public string Name { get; protected set; }
public virtual Element Parent { get; internal set; }
public virtual List<Element> Children { get; private set; }
public string Instructions { get; set; }
}

The problems:

How to make sure that any objects added to the Children property, gets a correct reference to the parent object (this)?

How to make sure that my object can be serialized in an orderly fashion?

How to enforce that initialization is done properly once the object has been de-serialized?