Silverlight Firestarter 2010 Session 4 - MVVM: Why and How? Tips and Patterns using MVVM and Service Patterns with Silverlight and WP7

Great session John!!!

Any chance of getting code samples for the reusable services classes?

Thanks!

I keep starting MVVM projects but cannot seem to keep them that way!! I am desperate to get my head around it so I am keen to see the code if possible.

Thanks

Thanks John!

This was one of the most important sessions to a lot of us trying to use the MVVM pattern and the right way of doing it. I wish you would have had this topic when you were in Tampa.

Thank you again for all you do in teaching us Silverlight.

Hi john
I read you many books like Data driven services with silverlight2.0 etc.But from SL2.0 to SL 4.0 there is lot of change, hope we will see a new book from your side soon.
 Now we are implemanting MVVM adn this webcast is very intersting ,  please share code of this demo ASAP so that we can have a base idea of MVVM+ services sepration 
 
thanks
pardeep kaushik

Hi, John,
I want to download your sample and slide, could you provide it?
Thanks!
Ted

Thanks John :)
It is really great help session to us. With this session I came to know lot of technics in MVVM.

Thanks John, your shows have been a great help

Hello John
Great video....i have a question about MVVM....is it ok to have more than 100 lines of code in the view model or Is it recommended to break a view model when its code is growing?
Thanks

@jopapa:Got it...Thanks for the reply John...One more question..you mentioned to use behaviors for listbox selection changed events...but that behavior cannot be most likley reused anywhere else which does not satisfy the purpose of a behavior...
Instead...i think its easy to invoke the command in the selection changed event in the code behind as opposed to writing 5 lines of XAML for behavior...I know its slightly against MVVM...
An thoughts on this?
Thanks

Hi John,
So what exactly would you put in the code behind (if anything)?  Coming from the ASPX world I'm still wrestling with seperating out the view model logic from the code behind.  Thanks very much for the demos and this firestarter has been great for getting a better understanding at the intent behind a lot of the controls.  I'll be watching silverlight TV regularly!
 
 
 

Hi John,

Great session, very clear and useful. I will use it from now on as a point of reference when evangalising MVVM. Nice to see areas like Services,  Design etc and even dependency injection implemented in a lightweight format.

Juan

Hi John,

Nice work ! Very clean implementation of MVVM, and brought in a very bright and understandable way, very nice to follow your session here !

I've downloaded the code, but i've got some minor reference problem, seems like missing next DLL's :

-Microsoft.Expression.Effects

-Microsoft.Expression.Interaction

- System.Windows.Interactivity

These give next errors :

Error 55 The property 'Triggers' does not exist on the type 'StackPanel' in the XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 21 30 BookShelf
Error 56 The tag 'EventTrigger' does not exist in XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 22 34 BookShelf
Error 57 The tag 'InvokeCommandAction' does not exist in XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 23 38 BookShelf
Error 58 The property 'Triggers' does not exist on the type 'StackPanel' in the XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 31 30 BookShelf
Error 59 The tag 'EventTrigger' does not exist in XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 32 34 BookShelf
Error 60 The tag 'InvokeCommandAction' does not exist in XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\AdminView.xaml 33 38 BookShelf
Error 61 The property 'Triggers' does not exist on the type 'ListBox' in the XML namespace 'http://schemas.microsoft.com/expression/2010/interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml 140 27 BookShelf
Error 62 The tag 'EventTrigger' does not exist in XML namespace 'http://schemas.microsoft.com/expression/2010/interactivity'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml 141 28 BookShelf
Error 63 The tag 'EventToCommand' does not exist in XML namespace 'clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Extras.SL4'. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml 142 29 BookShelf
Error 64 Could not load file or assembly 'System.Windows.Interactivity, Version=4.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. Het systeem kan het opgegeven bestand niet vinden. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml 1 1 BookShelf
Error 65 System.IO.FileNotFoundException was thrown on "H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml": Could not load file or assembly 'System.Windows.Interactivity, Version=4.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. Het systeem kan het opgegeven bestand niet vinden. H:\Dev\SilverLight4\SilverlightFirestarter\Src\All SLFS10 Session\SLFS10 Session 3 (WCF RIA Services) - Code\WCFRIAServices_Firestarter\RIAServicesWithRepositoryDemo\BookShelf\Views\BookView.xaml 1 1 BookShelf

Should i install Expression Blend or something like that, or where can i find the DLL's seperatly, as it seems they are not included in the zipped package.

Thx for any response,

Emmanuel Nuyttens

.NET Architect from Belgium.

Hi John, a quick question,, let's say I have a few VM and each of them may be shared by more than one view.  So do I create a few viewmodellocator or there's other alternative?

Hello John,
I downloaded and ran you the demo app.  Can you teach me how I can prevent user from triggering save operation when there's error on the edit child window.  Currently it allows user to click submit and returns "unsucessful" message but then it crashes after.
One more question, I followed the same aprroach to put jpg in images folder but somehow I can't display the image.  Any clue what might have gone wrong?
Thanks for your prompt reply.

I want to use Windows Authentication and so I changed the code in the BookClubService:-

    [RequiresAuthentication]
    [EnableClientAccess()]
    public class BookClubService : LinqToEntitiesDomainService<BookClubEntities>
    {

and used this in the App.xaml.cs file:-

webContext.Authentication = new WindowsAuthentication(); 

Now the service will not work because I am unauthorized. Why does this not work? At the moment I am experimenting on my home PC.

@EzaBlade - have you made the change in the Web.Config?

@deepeshm:
No I had not done that - thanks. Now it will display books without error but the Edt button is disabled even though it's Enabled property is bound to the User.IsAuthenticated property in the xaml.

I am still confused about the relationship between WCF and RIA.  
My application needs to support a silverlight client as well as non-silverlight clients such as android.  I'd like to implement the biz logic in one place, presumably running server side and accessable by WCF.  Does it make sense for the silverlight app to connect to those WCF services via RIA while the andriod client consumes those same WCF services by the traditional wsdl contract?
Your suggestions or pointers to material on this subject are greatly appreciated.
Cheers,Jeff

re: still confused above:  
Someone pointed me to the following Silverlight TV Video where John & friends answer my question perfectly:
http://channel9.msdn.com/shows/SilverlightTV/Silverlight-TV-26-Exposing-SOAP-OData-and-JSON-Endpoints-for-RIA-Services/ 
see also: http://forums.silverlight.net/forums/p/218286/520249.aspx#520249
Basically the answer is:  Yes I can develop my silverlight app using RIA and also provide wcf endpoints for OData, JSON, SOAP, etc.
Cool!!Jeff 
 

Hello John,

This was a fantastic presentation. Finally I have seen a way to encapsulate the DomainContext properly within a Service and expose only the CRUD operations to the client rather than the whole context.

So far so good, however I think you made it a bit too convienent leaving out the actual Delete, Add and Update the entities.

I have downloaded your code, but if I added a book to the Observablecollection within the ViewModel, that book is not added automatically to the Context.Books, same goes with Delete or Update, hence the whole Service concept breaks the state change trackability of RIA objects.

But in this example it seems the way the ViewModel's observable collection is populated, it has no connection to the context on the Service. Which makes sense in a way, since Services should be stateless.  By having this in mind, perhaps it is not a good idea to encapsulate the DomainContext within a Service after all.

What is your opinion on this, how would you extend your example to support Adding, updating and deleting books through the Service?

Many Thanks,
Houman

@Houman

If you dig deeper into John's code you will find that the ObservableCollections returned by his service are really WCF RIA Services SP1 Beta EntityList objects. Unlike a plain ObservableCollection, an EntityList is linked to the DomainContext's EntitySet. That means anything you add or remove from the EntityList is also being added and removed from the EntitySet. It also means that if an entity is deleted outside of your EntityList, from a second EntityList or from the DomainContext itself for example, it will be removed from your EntityList as well preventing zombie entities from eating your application.