How do I make this run asynchronously?

Question

I am writing a WPF application in C# and in it I need to query history in TFS, and I'm displaying the list of changesets I get back in a listview.

The listview ItemsSource is bound to an IEnumerable property called Changesets that is not loaded until the property is used:

public IEnumerable<Changeset> Changesets
{
  get
  {
    if (p_nChangesets == null)
    {
      p_nChangesets = TfsHelper.VCS.QueryHistory(Path, VersionSpec.Latest, 0,
                                                 RecursionType.Full, null,
                                                 new ChangesetVersionSpec(1),
                                                 VersionSpec.Latest, int.MaxValue, 
                                                 false, true, false, false)
                                                 .OfType<Changeset>();
    }
    return p_nChangesets;
  }
}

Now what happens is when the view loads, the listview is bound to this property so it immediately calls the property to get the collection of changesets. Sometimes this query runs slow so it takes a while to even see the window open. What I want to happen is the window displays immediately and the listview is empty until the changesets are found and then the listview is filled. But I don't know how to do this. I tried using a Task, but that had the same result:

public IEnumerable<Changeset> Changesets
{
  get
  {
    if (p_nChangesets == null)
    {
      Task<IEnumerable> task = Task<IEnumerable>.Run(() => TfsHelper.VCS.QueryHistory(
                                                           Path, VersionSpec.Latest, 0, 
                                                           RecursionType.Full, null,
                                                           new ChangesetVersionSpec(1),
                                                           VersionSpec.Latest, int.MaxValue, 
                                                           false, true, false, false));
      p_nChangesets = task.Result.OfType<Changeset>();
    }
    return p_nChangesets;
  }
}

Clearly, I don't know what I'm doing with tasks. Does anyone know how to make this do what I want?

Answer 1

Add IsAsync=True in your binding in XAML:

<ListView ItemsSource="{Binding ChangeSets, IsAsync=True}"/>