Question

The situation is like this: I have an Observable Collection that has a bunch of objects in it which I then display to a listbox using a binding. Then periodically, I get a message from an external server that gives me a new (or possibly the same) ordering for these objects. Right now, I just clear the observable collection, and add each item back in using the specified ordering.

This doesn’t look too nice. Is there a better way to go about doing this? I’d be really awesome if I could somehow get the listbox to reorder and have a nice reordering animation with it, but that might be asking too much.

I thought about adding the ordering as an attribute to each object in the ObservableCollection and then calling a sort on it. Would this look clean? My assumption is that it would be almost the same effect as clearing it and readding everything.

Thanks for any help!

Answer 1

I created a class that inherits from ObservableCollection. This class has a SetItems method where you need to pass in the newly ordered items. Key in this class is that it will suppress the collectionchanged event and thus will not refresh the listbox each time an item is added. It looks better and loads a lot faster.

public class SuperObservableCollection<T> : ObservableCollection<T>
{
    public void SetItems(IEnumerable<T> items)
    {
        suppressOnCollectionChanged = true;
        Clear();
        AddRange(items);
    }

    private bool suppressOnCollectionChanged;
    public void AddRange(IEnumerable<T> items)
    {
        suppressOnCollectionChanged = true;

        if (items != null)
        {
            foreach (var item in items)
                Add(item);
        }

        suppressOnCollectionChanged = false;
        NotifyCollectionChanged();
    }

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (!suppressOnCollectionChanged)
            base.OnCollectionChanged(e);
    }

    public void NotifyCollectionChanged()
    {
        OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }
}