Question

Is there a standardized way to sync a collection of Model objects with a collection of matching ModelView objects in C# and WPF? I’m looking for some kind of class that would keep the following two collections synced up assuming I only have a few apples and I can keep them all in memory.

Another way to say it, I want to make sure if I add an Apple to the Apples collection I would like to have an AppleModelView added to the AppleModelViews collection. I could write my own by listening to each collections’ CollectionChanged event. This seems like a common scenario that someone smarter than me has defined “the right way” to do it.

public class BasketModel
{
    public ObservableCollection<Apple> Apples { get; }
}

public class BasketModelView
{
    public ObservableCollection<AppleModelView> AppleModelViews { get; }
}

Answer 1

I may not exactly understand your requirements however the way I have handled a similar situation is to use CollectionChanged event on the ObservableCollection and simply create/destroy the view models as required.

void OnApplesCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{    
  // Only add/remove items if already populated. 
  if (!IsPopulated)
    return;

  Apple apple;

  switch (e.Action)
  {
    case NotifyCollectionChangedAction.Add:
      apple = e.NewItems[0] as Apple;
      if (apple != null)
        AddViewModel(asset);
      break;
    case NotifyCollectionChangedAction.Remove:
      apple = e.OldItems[0] as Apple;
      if (apple != null)
        RemoveViewModel(apple);
      break;
  }

}

There can be some performance issues when you add/remove a lot of items in a ListView.

We have solved this by: Extending the ObservableCollection to have an AddRange, RemoveRange, BinaryInsert methods and adding events that notify others the collection is being changed. Together with an extended CollectionViewSource that temporary disconnects the source when the collection is changed it works nicely.

HTH,

Dennis