Question

I ve start using prism with silverlight 3, but, we are trying to implement it to work with ADO.NET DataServices. The "DataServiceQuery" query type required to use with Silverlight, requires a Asyncronous call to be fired after the query. This will break ous Prism Pattern by what I can see. Any ideas to get only the data of the query to use in Prism Pattern? Correct-me anyone if i m wrong!

Answer 1

Making an Asynchronous call to your server doesn t break "Prism Pattern". When your view needs to query the server, its viewmodel fires an asynchronous request and provides a callback. Once callback is called, it handles the result and updates whatever properties it exposes to a view. This will result in view updating according to bindings you set up in your xaml.

Answer 2

PL is exactly right. There s really no patterns that Prism encourages that are incompatible with ADO.NET Data Services. There are just a few things you should know.

Here s a small sample. It s a little tricky... the complete event will sometimes fire outside of the UI thread, so you have to handle it with the dispatcher (at least in SL2 you did):

public class MyViewModel : BaseViewModel
{

     public Customer CustomerResult
     {
         ...
     }

     NorthwindEntities svcContext = null;
     public MyViewModel()
     {
            svcContext =
                new NorthwindEntities(new Uri("Northwind.svc", UriKind.Relative));

            DataServiceQuery<Customers> query =
                svcContext.Customers.Expand("Orders");

            // Begin the query execution.
                query.BeginExecute(WorkComplete, query);

     }



     private void WorkComplete(IAsyncResult result)
     {
          DataServiceQuery<Customers> query =
                    result.AsyncState as DataServiceQuery<Customers>;

          Customers returnedCustomer =
                    query.EndExecute(result).FirstOrDefault();

          //Execute with the dispatcher
          Dispatcher.CurrentDispatcher.BeginInvoke( () =>
          {
               CustomerResult = returnedCustomer;
          });
     }
}

Of course there is no exception handling in here, but you get the picture hopefully.

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