ASP.NET 4.0 Hosting & ASP.NET 4.5 Hosting BLOG

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Silverlight (and WPF) Hosting: How to make items stretch horizontally in a ListBox

clock September 16, 2011 07:46 by author Administrator


Sometimes we need to use controls like TextBox, TextBlock etc (that set their width automatically depending on content) in a ListBox’s ItemTemplate. If we need to draw Borders or assign Background colors to each such controls then we may end up having non-equal rows. Here’s a sample markup:


Here’s the output for the above XAML:


A quick thought would be to assign HorizontalContentAlignment property to Stretch for the TextBox but this wont work. We need to specify this property for the ListBoxItem that encapsulates our DataTemplate. Here’s a quick syntax for doing this using a style:

And here’s the output:

This should be fine in most case but sometimes we also need to wrap the text as highlighted using red arrows in the above image. Now setting TextWrapping property will have no effect as the TextBox thinks it can take all the horizontal space. This can be solved by disabling the horizontal scroll bar for the ListBox:

Here’s the final output:


RIA Service Hosting :: How to send complex types to the Client

clock September 13, 2011 06:38 by author Administrator


Entity Framework 4 allows us to create complex types. Typically, such types are used to get the result of a stored procedure. However, when we try to send such a complex type using a WCF RIA Domain Service, the following error is encountered.

What to do? Adding attributes to EF designer generated classes is a bad idea; Also, we cannot use partial classes to add attributes to an already defined property. However, luckily, WCF RIA Services uses metadata classes in conjunction with the entity model classes and hence we can always create a meta data class for our complex type and decorate one of the fields with a
[Key] attribute. E.g., If our stored procedure is returning StoredProcedure_Result, then we may just need to add the following in our DomainService.metadata.cs file:

Silverlight WCF Hosting :: Cross-Origin Resource Sharing (CORS) and WCF

clock July 5, 2011 08:45 by author Administrator

Yesterday I encountered the following question in the MSDN forums about calling a cross-domain WCF RESTful service from Chrome.

The problem with doing the above is because there is a cross-domain call to a WCF service. When you are using Chrome, the browser tries to find out if it can do the call by sending a cross-origin resource sharing (CORS) request, as explained in this article. In IE, you will most likely get a cross-domain exception.

After searching the web a bit, I found that the immediate solution is to change the supported HTTP method of the operation to “*”, and to add the special cross-origin headers to the outputted response, like so:

  "Access-Control-Allow-Origin", "*"); WebOperationContext.Current.OutgoingResponse.Headers.Add(   "Access-Control-Allow-Methods", "POST"); WebOperationContext.Current.OutgoingResponse.Headers.Add(
  "Access-Control-Allow-Headers", "Content-Type, Accept");

There are two problems with this solution:

You need to repeat these lines in each of your service methods.
The service method is called twice, once for the “preflight” request (the request with the OPTIONS HTTP verb), and a second time for the invocation itself.

So I took the time and written a special endpoint behavior that can be attached to any webHttpBinding based endpoint.

The code does the following:

1. Every response message gets the “Access-Control-Allow-Origin” header with the value of “*”, to tell the client that the service allowed the request from the client.

2. If the client sends a request to the service with the verb OPTIONS (this is referred to as a “preflight” request), the service will automatically return a 200 (ok) response with the required headers: “Access-Control-Allow-Headers” and “Access-Control-Allow-Methods” (in addition to the allow-origin header). Clients that look for the “allow” headers in the response will then send the original required request to the service.

The benefits of using this behavior is:

The code that returns the message with the headers is located in the behavior itself – no need to place it in each service method.

The behavior catches the OPTIONS request, and does not require running the service method twice.

You do not need to change any part of your service contract or service implementation. The behavior is only needed to be applied using configuration.

To implement this behavior I used a message inspector that checks the request and changes the response, and an operation invoker that wraps the unhandled operation invoker. The custom operation invoker handles the OPTIONS message requests, which otherwise would have caused the service to return an error message (because no method is set to handle “Options” requests).

The endpoint behavior can be attached to the endpoint through configuration, like so:

    <behavior name="webSupport">
      <webHttp />
      <CorsSupport />

    <add name="CorsSupport" type="WebHttpCors.CorsSupportBehaviorElement, WebHttpCors, Version=, Culture=neutral, PublicKeyToken=null" />
  <service name="Service.JSonService">
    <endpoint address="http://localhost:8080" behaviorConfiguration="webSupport” binding="webHttpBinding" contract="Service.IJSonService" />

Or, if you are using IIS to host your services, I also created a service host factory that creates a WebServiceHost and adds the behavior to every webHttpBinding based endpoint created by the host. To use it in your .svc file, just write something like this:

<%@ ServiceHost Language="C#" Debug="true" Service="Service.JSonService, Service" Factory="WebHttpCors.CorsWebServiceHostFactory, WebHttpCors" %>

To test the two hosts, open the webform1.aspx and change the target URL to access the IIS/self-hosted service.


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