Bind to a sorted ObservableCollection<T> in a ListBox

Question

I have a list of data objects in my Windows Phone 7 application called MyObjectList which inherits ObservableCollection<MyObject>. I keep the list in memory in a public property of App called MyObjects. My goal is to bind the data to a ListBox and have it sorted by MyObject.Name.

Currently, I have a ListBox in XAML with the name MyObjectsList and the following code in the constructor to link it up:

public MyObjectListView()
{
    InitializeComponent();
    this.MyObjectsList.ItemsSource = ((App)App.Current).MyObjects;
}

This works great. I add items to MyObjects and they show up in the ListBox. However, the data isn't sorted by name when it appears in the list. I tried the following change to get the data to be sorted:

    this.MyObjectsList.ItemsSource = ((App)App.Current).MyObjects
                                         .OrderBy(x => x.Name)

But when I do that, I don't see any objects reflected in the ListBox sorted or otherwise.

What can I do so that when I add an item to my ObservableCollection, it shows up sorted by .Name in the ListBox?

Answer 1

Take a look at http://mokosh.co.uk/post/2009/08/04/how-to-sort-observablecollection/.

It explains how to extend ObservableCollection to expose the underlying Items.Sort() method and then notify listeners that the collection has changed.

Also, This Post here.. might help you with it. It uses CollectionView.

Answer 2

You could use a sorted collection instead of your standard ObservableCollection. Someone wrote a SortedObservableCollection here:

http://phillters.wordpress.com/2009/05/14/sortedobservablecollection/

Answer 3

This doesn't help you for Silverlight, but for WPF 3.5/4, there's a better way to do this involving CollectionView

Answer 4

The problem with your example is the OrderBy method returns an IOrderedEnumerable type of object instead of an ObservableCollection.

Here's something you can do without implementing a custom collection like some of the other answers.

var sortedMyObjects = new ObservableCollection<MyObject>();
foreach (var myobj in ((App)App.Current).MyObjects.Orderby(x => x.Name))
    sortedMyObjects.Add(myobj);
this.MyObjectsList.ItemsSource = sortedMyObjects;

The other answers all suggest viable alternatives, but this will solve the problem in the question.

FWIW, in Silverlight 4 there is a PagedCollectionView, but Windows Phone 7's Silverlight is based on Silverlight 3 and that isn't available. I'm only mentioning this to keep you aware of it in anticipation of WP7 eventually updating to SL4.