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POHow to notify a client from wf4-wcf-server asynchronously?
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  1. POHow to notify a client from wf4-wcf-server asynchronously?
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    copied!<p>during the last days I spent a lot of time to find a solution on how to send simple messages from a workflow (WF4)-server to a client (in my case WPF).</p> <p>There exist some examples how to reply on a request (via callback), but I can not find any example how to contact the client asynchronously.</p> <p>I want to be able to have a communication like this:</p> <ul> <li>[8:00 am] Client: "Hello Server, this is my request. Please start your workflow 'MakeCoffee' using this recipe.". </li> <li>[8:01 am] WF-Server: "Hello Client, I'm on it." </li> <li>[8:05 am] WF-Server: "I can't find any coffee. I will buy some."</li> <li>[8:10 am] WF-Server: "I am boiling the water." </li> <li>[8:15 am] WF-Server: "Do you want sugar?"</li> <li>[8:17 am] Client: "Yes." </li> <li>[8:18 am] WF-Server: "I am done."</li> </ul> <p>Until now, I found these solutions:</p> <h2>1. WCF - Service with CallBack-Channel</h2> <p><a href="https://stackoverflow.com/questions/5739501/how-can-a-wcf-service-raise-events-to-its-clients">This example</a> seems to be pretty cool, but I do not see how to use this with my Workflow-Service - for there is no "implementing service" class. Everything is visual, so I can not apply the "SubscribeClient"-method (or at least I do not know where to place the service implementation).</p> <h2>2. Workflow with notifying events</h2> <p><a href="http://code.msdn.microsoft.com/windowsdesktop/Windows-Workflow-eaa24bdb#content" rel="nofollow noreferrer">This example</a> is a nice solution - but (for my understanding) this does not work with a separate workflow-server - it seems to require that the workflow-server and the client are the same.</p> <h2>3. Accessing OperationContext</h2> <p><a href="http://msdn.microsoft.com/en-us/library/ee834517.aspx" rel="nofollow noreferrer">This example</a> creates a WorkflowServiceHost on client-side, but it is not very easy to handle and I can't adjust it to my requirements.</p> <p><strong>Does anyone know a handy solution/pattern on how to send messages from a (separate) workflow-server to a client?</strong> The client does not know, when the server might send him messages and how many it will be.</p> <p>I am kind of new to WF4 and would be very thankful for every hint/advise/idea.</p> <p>Thanks in advance,</p> <p>Timo</p> <h1>UPDATE</h1> <p>According to the comment from Maurice, I tried to use a simple service in my client, but unfortunately, my client does not receive and show any of the messages.</p> <p>This is my client-code:</p> <pre class="lang-cs prettyprint-override"><code>public partial class MainWindow : Window { private ServiceHost _serviceHost; private void Window_Loaded(object sender, RoutedEventArgs e) { ApplicationInterface._app = this; //prepare the serviceHost string clientAddress = "http://localhost:8000/ClientService"; System.ServiceModel.Channels.Binding bBinding = new BasicHttpBinding(); _serviceHost.AddServiceEndpoint(typeof(IClientService), bBinding, clientAddress); _serviceHost.Open(); } public ListBox GetEventListBox() { return this.lstEvents; } } </code></pre> <p>This is my IClientService-Interface:</p> <pre class="lang-cs prettyprint-override"><code>[ServiceContract] public interface IClientService { [OperationContract(IsOneWay=true)] void MeldeStatus(String statusText); } </code></pre> <p>This is the implementation of the IClientService-Interface:</p> <pre class="lang-cs prettyprint-override"><code>public class ClientService : IClientService { public void MeldeStatus(string statusText) { ApplicationInterface.AddEvent(statusText); } } </code></pre> <p>This is the static ApplicationInterface:</p> <pre class="lang-cs prettyprint-override"><code>public static class ApplicationInterface { public static MainWindow _app { get; set; } public static void AddEvent(String eventText) { if (_app != null) { new ListBoxTextWriter(_app.GetEventListBox()).WriteLine(eventText); } } } </code></pre> <p>And this the ListBoxTextWriter-class, which should add the messages to a given ListBox:</p> <pre class="lang-cs prettyprint-override"><code>public class ListBoxTextWriter : TextWriter { const string textClosed = "This TextWriter must be opened before use"; private Encoding _encoding; private bool _isOpen = false; private ListBox _listBox; public ListBoxTextWriter() { // Get the static list box _listBox = ApplicationInterface._app.GetEventListBox(); if (_listBox != null) _isOpen = true; } public ListBoxTextWriter(ListBox listBox) { this._listBox = listBox; this._isOpen = true; } public override Encoding Encoding { get { if (_encoding == null) { _encoding = new UnicodeEncoding(false, false); } return _encoding; } } public override void Close() { this.Dispose(true); } protected override void Dispose(bool disposing) { this._isOpen = false; base.Dispose(disposing); } public override string ToString() { return ""; } public override void Write(char value) { if (!this._isOpen) throw new ApplicationException(textClosed); ; this._listBox.Dispatcher.BeginInvoke (new Action(() =&gt; this._listBox.Items.Add(value.ToString()))); } public override void Write(string value) { if (!this._isOpen) throw new ApplicationException(textClosed); ; if (value != null) this._listBox.Dispatcher.BeginInvoke (new Action(() =&gt; this._listBox.Items.Add(value))); } public override void Write(char[] buffer, int index, int count) { String toAdd = ""; if (!this._isOpen) throw new ApplicationException(textClosed); ; if (buffer == null || index &lt; 0 || count &lt; 0) throw new ArgumentOutOfRangeException("buffer"); if ((buffer.Length - index) &lt; count) throw new ArgumentException("The buffer is too small"); for (int i = 0; i &lt; count; i++) toAdd += buffer[i]; this._listBox.Dispatcher.BeginInvoke (new Action(() =&gt; this._listBox.Items.Add(toAdd))); } } </code></pre> <p>My WF-Server uses this Send-Activity:</p> <pre class="lang-html prettyprint-override"><code>&lt;Send Action="MeldeStatus" EndpointConfigurationName="BasicHttpBinding_Client" sap:VirtualizedContainerService.HintSize="255,90" OperationName="MeldeStatus" ProtectionLevel="None" ServiceContractName="p:IClientService"&gt; &lt;SendParametersContent&gt; &lt;p1:InArgument x:TypeArguments="x:String" x:Key="statusText"&gt;Yes, it works.&lt;/p1:InArgument&gt; &lt;/SendParametersContent&gt; &lt;/Send&gt; </code></pre> <p>This is the configuration of my endpoint at the WF-server:</p> <pre class="lang-html prettyprint-override"><code>&lt;system.serviceModel&gt; &lt;bindings&gt; &lt;basicHttpBinding&gt; &lt;binding name="DefaultHTTPBinding" allowCookies="true" /&gt; &lt;/basicHttpBinding&gt; &lt;/bindings&gt; &lt;behaviors&gt; &lt;serviceBehaviors&gt; &lt;behavior&gt; &lt;serviceMetadata httpGetEnabled="true"/&gt; &lt;serviceDebug includeExceptionDetailInFaults="true"/&gt; &lt;/behavior&gt; &lt;/serviceBehaviors&gt; &lt;/behaviors&gt; &lt;services&gt; &lt;service name="WFServer.ReklamationErfassen"&gt; &lt;endpoint address="http://localhost:7812/ReklamationErfassen.xamlx" binding="basicHttpBinding" bindingConfiguration="DefaultHTTPBinding" contract="IReklamationService" /&gt; &lt;/service&gt; &lt;/services&gt; &lt;client&gt; &lt;endpoint address="http://localhost:8000/ClientService" binding="basicHttpBinding" bindingConfiguration="DefaultHTTPBinding" contract="IClientService" name="BasicHttpBinding_Client" /&gt; &lt;/client&gt; &lt;/system.serviceModel&gt; &lt;system.webServer&gt; &lt;modules runAllManagedModulesForAllRequests="true"/&gt; &lt;/system.webServer&gt; </code></pre> <p>I do not get any messages, error or warnings - can somebody please have a quick check on the given code?</p> <p>Thanks again,<br> Timo</p>
 

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