/// <summary>
/// Add object and return the index position.
/// </summary>
public int Add(T obj)
{
// ... check for unused indexes first ...
if (_UnusedIndexes.Count > 0)
{
var lastIndex = _UnusedIndexes.Count - 1;
var i = _UnusedIndexes[lastIndex];
_UnusedIndexes.RemoveAt(lastIndex);
_Objects[i] = new _ObjectItem {
Object = obj, ValidObjectIndex = _ValidObjects.Count
};
_ValidObjects.Add(new _ValidObjectItem {
Object = obj, ObjectIndex = i
});
return(i);
}
else
{
var i = _Objects.Count;
_Objects.Add(new _ObjectItem {
Object = obj, ValidObjectIndex = _ValidObjects.Count
});
_ValidObjects.Add(new _ValidObjectItem {
Object = obj, ObjectIndex = i
});
return(i);
}
}
/// <summary>
/// Removes the object at the given index and sets the entry to 'default(T)' (which is usually 0 or null).
/// </summary>
public void Remove(int objIndex)
{
if (objIndex < 0 || objIndex >= _Objects.Count)
{
throw new IndexOutOfRangeException("objIndex = " + objIndex);
}
_ObjectItem itemRemoved = _Objects[objIndex];
if (itemRemoved.ValidObjectIndex == -1)
{
return; // (already deleted, nothing to do)
}
if (objIndex == _Objects.Count - 1) // (if removing from end, simply "pop" it)
{
_Objects.RemoveAt(objIndex);
}
else // (clear this entry and record it for reuse)
{
_Objects[objIndex] = new _ObjectItem {
Object = default(T), ValidObjectIndex = -1
};
_UnusedIndexes.Add(objIndex);
}
// ... swap valid-object-list entry with end and remove it ...
var voLastIndex = _ValidObjects.Count - 1;
if (itemRemoved.ValidObjectIndex != voLastIndex) // (if the item removed references the last "valid object" entry, just simply remove it [skip the block])
{
var voEnd = _ValidObjects[voLastIndex];
_ValidObjects[itemRemoved.ValidObjectIndex] = voEnd; // (move end entry in place of removed item)
var itemToUpdate = _Objects[voEnd.ObjectIndex]; // (need to update the indexed object's "valid object" index via the link-back index)
itemToUpdate.ValidObjectIndex = itemRemoved.ValidObjectIndex;
_Objects[voEnd.ObjectIndex] = itemToUpdate;
}
_ValidObjects.RemoveAt(voLastIndex); // (last item is moved down now in place of the deleted object, so this just really decrements the count.)
}
