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.