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

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 2

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.

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