ReadAsDataContract exception while reading namespace

namespacesrestwcf

I'm trying to consume twitter's REST api mentioned at this link using WCF REST starter kit mentioned at this link.

I'm using the same objects in DataContract as mentioned in the article – statusList and status.

[assembly: ContractNamespace("", ClrNamespace = "TwitterShell")]
[CollectionDataContract(Name = "statuses", ItemName = "status")]
public class statusList : List<status> { }
public class user
{
    public string id;
    public string name;
    public string screen_name;
}
public class status
{
    public string id;
    public string text;
    public user user;
}

I'm reading the XML contents using ReadAsDataContract() method.

HttpClient http = new HttpClient("http://twitter.com/statuses/");
http.TransportSettings.Credentials =
    new NetworkCredential("{username}", "{password}");
HttpResponseMessage resp = http.Get("friends_timeline.xml");
resp.EnsureStatusIsSuccessful();
statusList sList = resp.Content.ReadAsDataContract<statusList>();

And I get the following exception. I have not defined the following namespace at all.

Error in line 1 position 24. Expecting element 'statuses' from namespace 'http://schemas.datacontract.org/2004/07/sitename'.. Encountered 'Element' with name 'statuses', namespace ''.

Please help. Thanks.

Best Answer

Just don't do it. You are in for a world of pain if you try using Datacontracts and operation contracts to access non-wcf services.

Ok, so I guess that was a bit unfair leaving you high and dry without an alternative, so try this:

var response = client.Get("http://twitter.com/statuses/friends_timeline.xml");

var statuses = response.Content.ReadAsXElement();

var statusQuery = from st in statuses.Elements("status")
                  select new status {
                                id = st.Element("id").Value,
                                text = st.Element("text").Value,
                                user = (from us in st.Elements("user")
                                        select new user {
                                             id = us.Element("id").Value,
                                             name = us.Element("name").Value,
                                             screen_name = us.Element("screen_name").Value
                                                         }).FirstOrDefault()
                                      };
var statuses = statusQuery.ToList();

Using Linq to XML to create objects from the XML document allows you to avoid the magic of serializers and completely control the names and datatypes of your client side objects. It would be really easy to wrap this as a new HttpContent extension method so that you could simply do:

var statuses = response.Content.ReadAsTwitterStatuses();

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

Javascript – How to declare a namespace in JavaScript

I use the approach found on the Enterprise jQuery site:

Here is their example showing how to declare private & public properties and functions. Everything is done as a self-executing anonymous function.

(function( skillet, $, undefined ) {
    //Private Property
    var isHot = true;

    //Public Property
    skillet.ingredient = "Bacon Strips";

    //Public Method
    skillet.fry = function() {
        var oliveOil;

        addItem( "\t\n Butter \n\t" );
        addItem( oliveOil );
        console.log( "Frying " + skillet.ingredient );
    };

    //Private Method
    function addItem( item ) {
        if ( item !== undefined ) {
            console.log( "Adding " + $.trim(item) );
        }
    }
}( window.skillet = window.skillet || {}, jQuery ));

So if you want to access one of the public members you would just go skillet.fry() or skillet.ingredients.

What's really cool is that you can now extend the namespace using the exact same syntax.

//Adding new Functionality to the skillet
(function( skillet, $, undefined ) {
    //Private Property
    var amountOfGrease = "1 Cup";

    //Public Method
    skillet.toString = function() {
        console.log( skillet.quantity + " " +
                     skillet.ingredient + " & " +
                     amountOfGrease + " of Grease" );
        console.log( isHot ? "Hot" : "Cold" );
    };
}( window.skillet = window.skillet || {}, jQuery ));

The third `undefined` argument

The third, undefined argument is the source of the variable of value undefined. I'm not sure if it's still relevant today, but while working with older browsers / JavaScript standards (ecmascript 5, javascript < 1.8.5 ~ firefox 4), the global-scope variable undefined is writable, so anyone could rewrite its value. The third argument (when not passed a value) creates a variable named undefined which is scoped to the namespace/function. Because no value was passed when you created the name space, it defaults to the value undefined.

Best Answer

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

Javascript – How to declare a namespace in JavaScript

The third undefined argument

Related Topic

The third `undefined` argument