how do you implement Async Operations in C# and MVVM?

Question

hi what is the easiest way to implement asynch operations on WPF and MVVM, lets say if user if user hits enter when on a field i want to launch a command and then return back wh

Answer 1

In Shawn Wildermuth's MSDN Article he did something like this: check out the article here: http://msdn.microsoft.com/en-us/magazine/dd458800.aspx

and his more recent blog post here: http://wildermuth.com/2009/12/15/Architecting_Silverlight_4_with_RIA_Services_MEF_and_MVVM_-_Part_1

public interface IGameCatalog
{
  void GetGames();
  void GetGamesByGenre(string genre);
  void SaveChanges();

  event EventHandler GameLoadingComplete;
  event EventHandler GameLoadingError;
  event EventHandler GameSavingComplete;
  event EventHandler GameSavingError;
}

with an implementation like this:

public class GameCatalog : IGameCatalog
{
  Uri theServiceRoot;
  GamesEntities theEntities;
  const int MAX_RESULTS = 50;

  public GameCatalog() : this(new Uri("/Games.svc", UriKind.Relative))
  {
  }

  public GameCatalog(Uri serviceRoot)
  {
    theServiceRoot = serviceRoot;
  }

  public event EventHandler GameLoadingComplete;
  public event EventHandler GameLoadingError;
  public event EventHandler GameSavingComplete;
  public event EventHandler GameSavingError;

  public void GetGames()
  {
    // Get all the games ordered by release date
    var qry = (from g in Entities.Games
               orderby g.ReleaseDate descending
               select g).Take(MAX_RESULTS) as DataServiceQuery;

    ExecuteGameQuery(qry);
  }

  public void GetGamesByGenre(string genre)
  {
    // Get all the games ordered by release date
    var qry = (from g in Entities.Games
               where g.Genre.ToLower() == genre.ToLower()
               orderby g.ReleaseDate
               select g).Take(MAX_RESULTS) as DataServiceQuery;

    ExecuteGameQuery(qry);
  }

  public void SaveChanges()
  {
    // Save Not Yet Implemented
    throw new NotImplementedException();
  }

  // Call the query asynchronously and add the results to the collection
  void ExecuteGameQuery(DataServiceQuery qry)
  {
    // Execute the query
    qry.BeginExecute(new AsyncCallback(a =>
    {
      try
      {
        IEnumerable results = qry.EndExecute(a);

        if (GameLoadingComplete != null)
        {
          GameLoadingComplete(this, new GameLoadingEventArgs(results));
        }
      }
      catch (Exception ex)
      {
        if (GameLoadingError != null)
        {
          GameLoadingError(this, new GameCatalogErrorEventArgs(ex));
        }
      }

    }), null);
  }

  GamesEntities Entities
  {
    get
    {
      if (theEntities == null)
      {
        theEntities = new GamesEntities(theServiceRoot);
      }
      return theEntities;
    }
  }
}