Honestly though, if recalculating takes .5 seconds, then recalculating from scratch every time may be unrealistic.
Is it possible to keep a "running total"? In other words, if the parent object were notified each time a specific child's specific property was changed, could it do an incremental adjustment?
Presumably this would require knowing the previous value too - but it may be worth coming up with a way to provide that. The previous post does that with a callback to the parent - which is totally workable.
Suppose the child had a Friend/internal PreviousWeight property?
public class Child : ...
{
private int _weight;
private int _lastWeight;
public int Weight
{
get { return _weight; }
set { _lastWeight = _weight; _weight = value; PropertyHasChanged("Weight"); }
}
internal int LastWeight
{ get { return _lastWeight; } }
}
Then your collection could update the TotalWeight value by backing out the LastWeight and adding in the new Weight each time it handles PropertyChanged for Weight. That'd be a lot faster than trying to recalc from scratch every time.
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