silverlight, using Observables on WCF calls, casting IEvent<T> where T : AsyncCompletedEventArgs -

i have question using observables in silverlight 4 make wcf calls. consider simple webservice call below.

var adminclient = serviceproxy.withfactory<authenticationclient>(); var results= observable.fromevent<authorizeadministratorcompletedeventargs>(    s => adminclient.authorizeadministratorcompleted += s,    s => adminclient.authorizeadministratorcompleted -= s).observeondispatcher();  adminclient.authorizeadministratorasync(); results.subscribe(e => {    //enable ui button }); 

i have implemented extension method, wraps subscribe method, error validation on return.

---

on return results.subscribe(e =>

e system.collections.generic.event<authorizeadministratorcompletedeventargs> 

almost every query have different return type such as:

e system.collections.generic.event<asynccompletedeventargs> 

if had wrapper looked this, how can cast every type of xxxcompletedeventargs base type asynccompletedeventargs can access e.eventargs , inspect error property

public static idisposable subscribe<tsource>(this iobservable<tsource> source, action<tsource> onnext = null, action onerror = null, action onfinal = null) {     action<tsource> onnextwrapper = (s) =>     {                        var args = (system.collections.generic.ievent<asynccompletedeventargs>)s;      try        {                                       if (wcfexceptionhandler.handleerror(args.eventargs))              {                 if (onnext != null)                    onnext(s);              }              else              {                 if (onerror != null)                    onerror();              }         }                 {            if (onfinal != null)               onfinal();         }    };     return source.subscribe<tsource>(onnextwrapper, (e) => { throw e; }); } 

the code above fail

unable cast object of type 'system.collections.generic.event1[myproject.provider.authorizeadministratorcompletedeventargs]' type 'system.collections.generic.ievent1[system.componentmodel.asynccompletedeventargs]'

this method definition of wcfexceptionhandler.handleerror(args.eventargs))

public static bool handleerror(asynccompletedeventargs e) 

i'd change extension method acts handle the events non blocking operator (much same majority of rx extension method operators). like:

public static iobservable<ievent<teventargs>> gethandledevents<teventargs>(this iobservable<ievent<teventargs>> source)     teventargs : asynccompletedeventargs {     return observable.createwithdisposable<ievent<teventargs>>(observer =>         {             return source.subscribe(evt =>                 {                     try                     {                         if (wcfexceptionhandler.handleerror(evt.eventargs))                         {                             observer.onnext(evt);                         }                         else                         {                             observer.onerror(new exception("some exception"));                         }                     }                                         {                         observer.onerror(new exception("some other exception"));                     }                 },                  observer.onerror,                  observer.oncompleted);         }); } 

then call through:

results.gethandledevents()   .finally(() => dosomethingfinally())   .subscribe(e =>   {    //enable ui button   },   ex => handleexception(ex),   () => handlecomplete()); 

i think should solve issues events funnel through original type , ensures handleerror gets event args correct type.