c# - WCF Callback not calling back -

i have read many articles here on so, , on msdn , code project. , still answer eludes me.

i have created wcf service has callback contract, , windows forms app (test harness) implements callback interface.

here interfaces:

[servicecontract] public interface icacheservice {     [operationcontract]     bool addtocache(string type, string key, string source, object item, int duration);       [operationcontract]     bool remove(string key); }    [servicecontract(sessionmode=sessionmode.required, callbackcontract=typeof(isearchcallback))] public interface icachesearch {     [operationcontract(isoneway=true)]     void searchcache(string source); }    public interface isearchcallback {     [operationcontract(isoneway=true)]     void oncallback(object data); } 

my service (left out add , remove conserve space - work expected):

[servicebehavior(instancecontextmode = instancecontextmode.single, concurrencymode=concurrencymode.multiple)] public class cachingservice : icacheservice, icachesearch, idisposable {     private list<icache> _cachelist = new list<icache>();     private isearchcallback _callback = null;       public void searchcache(string source)     {         try         {             _callback = operationcontext.current.getcallbackchannel<isearchcallback>();             list<object> items = new list<object>();             foreach (icache cache in this._cachelist)             {                 foreach (cacheitem item in cache.getcacheitemsbysource(source))                 {                     items.add(item.value);                 }             }              readonlycollection<object> outlist = new readonlycollection<object>(items);             _callback.oncallback(outlist);         }         catch { }     } } 

my service hosted in windows service. here system.servicemodel section app.config:

  <system.servicemodel>     <bindings>       <wshttpbinding>         <binding            name="wshttpbinding_icacheservice"            closetimeout="00:01:00"            opentimeout="00:01:00"            receivetimeout="00:01:00"            sendtimeout="00:01:00"            maxbufferpoolsize="2147483647"            maxreceivedmessagesize="2147483647">           <readerquotas maxarraylength="2147483647" maxbytesperread="2147483647" maxdepth="2147483647" maxnametablecharcount="2147483647" maxstringcontentlength="2147483647"/>         </binding>       </wshttpbinding>       <wsdualhttpbinding>         <binding           name="wsdualhttpbinding_icachesearch"           closetimeout="00:01:00"           opentimeout="00:01:00"           receivetimeout="00:01:00"           sendtimeout="00:01:00"           maxbufferpoolsize="2147483647"           maxreceivedmessagesize="2147483647"           clientbaseaddress="http://localhost:5057/wsdualhttpbinding"           usedefaultwebproxy="true"           transactionflow="false">           <readerquotas maxarraylength="2147483647" maxbytesperread="2147483647" maxdepth="2147483647" maxnametablecharcount="2147483647" maxstringcontentlength="2147483647"/>         </binding>       </wsdualhttpbinding>     </bindings>     <behaviors>       <servicebehaviors>         <behavior>           <servicemetadata httpgetenabled="true" />           <servicedebug includeexceptiondetailinfaults="false"/>         </behavior>       </servicebehaviors>     </behaviors>     <services>       <service name="cacheservice.cachingservice">         <host>           <baseaddresses>             <add baseaddress="http://localhost:5055/cachingservice/"/>           </baseaddresses>         </host>         <endpoint address="search" binding="wsdualhttpbinding" contract="cacheservice.icachesearch" />         <endpoint address="" binding="wshttpbinding" contract="cacheservice.icacheservice" />         <endpoint address="mex" binding="mexhttpbinding" contract="imetadataexchange" />       </service>     </services>     <client>       <endpoint address="http://localhost:5055/cachingservice/search" binding="wsdualhttpbinding"           bindingconfiguration="wsdualhttpbinding_icachesearch" contract="cacheservice.icachesearch"           name="wsdualhttpbinding_icachesearch" />       <endpoint address="http://localhost:5055/cachingservice" binding="wshttpbinding"     bindingconfiguration="wshttpbinding_icacheservice" contract="cacheservice.icacheservice"     name="wshttpbinding_icacheservice" />     </client>   </system.servicemodel> 

finally, created simple windows forms app test. declared as:

[callbackbehavior(usesynchronizationcontext = false, concurrencymode = concurrencymode.single)] public partial class form1 : form, cacheservice.icachesearchcallback {     instancecontext context = null;     cacheservice.cacheserviceclient _service = null;     cacheservice.cachesearchclient _proxy = null;      private void form1_load(object sender, eventargs e)     {         _synccontext = system.threading.synchronizationcontext.current;         _service = new cacheservice.cacheserviceclient();         this.datagridview1.autogeneratecolumns = true;          context = new instancecontext(this);         _proxy = new cacheservice.cachesearchclient(context);          refreshlist();     }       private void refreshlist()     {         _proxy.searchcache("mysource");     }       public void oncallback(object data)     {         this._data = data;         this.datagridview1.datasource = this._data;     } 

the call service (_proxy.searchcache("mysource")) executes method on service , service calls _callback.oncallback(outlist). callback method implemented in test app never called , data never conveyed test app.

again, have looked @ every recent wcf article on , many other blogs , code sites. feel need pair of eyes point out obvious can work.

many thanks,

robert