Why does CollectionViewSource.GetDefaultView(…) return the wrong CurrentItem from inside a Task thread?

Question

I have what I think is a fairly standard setup, a ListBox backed by an ObservableCollection.

I have some work to do with the Thing

Answer 1

I believe CollectionViewSource.GetDefaultView is effectively thread-static - in other words, each thread will see a different view. Here's a short test to show that:

using System;
using System.Windows.Data;
using System.Threading.Tasks;

internal class Test
{
    static void Main() 
    {
        var source = "test";
        var view1 = CollectionViewSource.GetDefaultView(source);
        var view2 = CollectionViewSource.GetDefaultView(source);        
        var view3 = Task.Factory.StartNew
            (() => CollectionViewSource.GetDefaultView(source))
            .Result;

        Console.WriteLine(ReferenceEquals(view1, view2)); // True
        Console.WriteLine(ReferenceEquals(view1, view3)); // False
    }        
}

If you want your task to work on a particular item, I suggest you fetch that item before starting the task.