Sharing assemblies using Portable Class Library with DataAnnotations

Question

I have created a portable class library called DataContracts that contains my projects Messages and Views. Standard stuff like GetStockItemByIDRequest and StockView are contained in it.

The problem lies when I attempt to add DataAnnotations by using System.ComponentModel.DataAnnotations for some of my Views as such.

[DataContract]
public class StockView
{
    [Required]
    [DataMember]
    public Guid StockID { get; set; }

    [Required]
    [DataMember]
    public string Name { get; set; }
}

I can successfully add the System.ComponentModel.DataAnnotations to my Portable Class Library project and can successfully reference it in my Windows Phone 8 app and can even create a new instance of my view as such StockView View = new StockView(); within my Windows Phone App BUT if I try to use either Newtonsoft.Json or System.Net.Http.HttpClient by doing something like

HttpClient client = new HttpClient();
HttpResponseMessage response = await client.GetAsync("http://myservice.com");
T result = await response.Content.ReadAsAsync<T>();

OR

T result = await Newtonsoft.Json.JsonConvert.DeserializeObjectAsync<T>("{}");

ie: where deserialization is involved...

I am faced with the error Could not load file or assembly 'System.ComponentModel.DataAnnotations, Version=2.0.5.0'. Which I assume is because it doesn't appear that System.ComponentModel.DataAnnotations is supported in Windows Phone 8 (but then why can I add it as a reference to my PCL?).

So my questions are, why isn't this error invoked when I create a new instance of these classes directly and secondly how do I work around this?

Answer 1

Unfortunately DataAnnotations is not currently portable. While a bit complicated, you can probably work around that by writing your own DataAnnotation attributes in a PCL, and creating an assembly with the same name for .NET Framework projects which type-forwards the attributes to the "real" versions. See this answer for some more details on this.

Answer 2

OK, so it turns out that my original assumptions were completely wrong. You absolutely can reference the System.ComponentModel.DataAnnotations namespace from a Windows Phone 8 project.

Basically it comes down to counterintuatively referencing the silverlight version of the dll which can be located in C:\Program Files (x86)\Microsoft SDKs\Silverlight\v4.0\Libraries\Client\System.ComponentModel.DataAnnotations.dll

For more information about how to build portable class libraries I suggest referring to this article .