Skip to main content

One way to use Dispatcher in a Silverlight application

Daca suntem intr-o aplicatie MVVM folosind Siverlight, in unele situatii o sa avem nevoie Dispatcher pentru a executa cod pe UI thread.
O varianta este de a trasmite o instanta la Dispatcher prin constructor sau cand se face apelul la o metoda data.
public class Context()
{
...
Context(Dispatcher dispatcher)
{
_dispatcher = dispatcher;
}
..
{
_dispatcher.BeginInvoke( () => { ... } );
}
}
O alta varianta destul de des intalnita este sa se obtina o referinta la Distapcher direct prin apelul:
Deployment.Current.Dispatcher
Ambele variante functioneaza fara nici o problema. Problema este ca clasele care folosesc acest Dispatcher o sa fie coupled. Aceasta problema se poate observa cel mai usor in momentul in care se scriu teste. Daca testele o sa reluze din brower de exemplu, pana la sfarsitul testelor, threadul de UI o sa fie blocat de rularea acestora, din aceasta cauza nu o sa se ajunga ca codul apelat prin Dispatcher sa fie executat. Pe langa acest lucru in teste dorim sa putem controla cand se ruleaza acest cod.
O varianta este sa ne definim o interfata pentru dispatcher-ul de UI, prin intermediul careia sa se poata rula cod pe UI thread. In acest mod, nu o sa mai fie coupled dispatcher-ul de restul aplicatiei. Iar in cazul in care dorim ca codul sa fie executat pe un alt thread sau in alt mod o sa fie nevoie sa ne implementam diferit acesta clasa( de exemplu pentru teste).
public interface IUiDispatcher
{
void Invoke(Action action);
}
public class UiDispatcher : IUiDispatcher
{
private readonly Dispatcher _dispatcher;

public UiDispatcher(Dispatcher dispatcher)
{
_dispatcher = dispatcher;
}

public void InvokeOnUiThread(Action action)
{
// Verificam daca suntem pe UI thread.
if( _dispatcher.CheckAccess())
{
action.Invoke();
}
else
{
_dispatcher.BeginInvoke(action);
}
}
}
Enjoy!

Comments

  1. Aha - asa se intampla intotdeauna cand nu se lucreaza test-first, desi pare mai greu la inceput..

    Si in WPF sau WinForms se intampla la fel: lumea folosea o varianta de ModelViewPresenter in speranta ca ulterior sa poata testa persenter-ul, doar ca sa descopere ca s-a grabit cineva si afisa un message box direct, dintr-o gramada de presentere - sa vezi refactoring dupa cand trebuiau scrise testele.. :)

    ReplyDelete

Post a Comment

Popular posts from this blog

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…