public DoubleLink Insert(string title)
{
// Creates a link, sets its link to the first item and then makes this the first item in the list.
DoubleLink link = new DoubleLink(title);
link.NextLink = _first;
if (_first != null)
_first.PreviousLink = link;
_first = link;
return link;
}
public DoubleLink Delete()
{
// Gets the first item, and sets it to be the one it is linked to
DoubleLink temp = _first;
if (_first != null)
{
_first = _first.NextLink;
if (_first != null)
_first.PreviousLink = null;
}
return temp;
}
public DoubleLink Delete(DoubleLink link)
{
DoubleLink temp = _first;
if (link == temp || link == null)
temp = Delete ();
else {
if (link.PreviousLink != null) {
link.PreviousLink.NextLink = link.NextLink;
}
if (link.NextLink != null)
link.NextLink.PreviousLink = link.PreviousLink;
temp = link.PreviousLink;
}
return temp;
}
///// New operations
public void InsertAfter(DoubleLink link, string title)
{
if (link == null || string.IsNullOrEmpty(title))
return;
DoubleLink newLink = new DoubleLink(title);
newLink.PreviousLink = link;
// Update the 'after' link's next reference, so its previous points to the new one
if (link.NextLink != null)
link.NextLink.PreviousLink = newLink;
// Steal the next link of the node, and set the after so it links to our new one
newLink.NextLink = link.NextLink;
link.NextLink = newLink;
}
public DoubleLinkedList()
{
_first = null;
}