C# – XDocument doesn’t appear to exist in System.Xml namespace

cwindows-phone-7xml

I'm having what I think will probably be a really simple problem, in developing my first WP7 app I've come to the stage of accessing my Site's api and parsing the XML, however I'm stumbling just at trying to use XDocument.

I search around and found this example code: Load an XML file from a website into XDocument (Silverlight and Windows Phone 7) but the XDocument type does not exist, I understand it is supposed to exist in the System.Xml namespace which I am using, but the error still remains, what have I missed?

Developing on Visual Studio 2010 Express for Windows Phone, code for this class is below:

using System;
using System.Net;
using System.IO;
using System.Xml;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace Application
{
    public class DataRetriever
    {
        public void parseNewsXML()
        {
            WebClient client = new WebClient();
            client.OpenReadCompleted += (sender, e) =>
                {
                    if (e.Error != null)
                        return;

                    Stream str = e.Result;
                    XDocument xdoc = XDocument.Load(str);
                };
        }
   }

Exact error being thrown is:
Error 1 The type or namespace name 'XDocument' could not be found (are you missing a using directive or an assembly reference?)

Thanks in advance

Best Answer

For Silverlight, that class is in System.Xml.Linq.dll, according to MSDN - so add a reference to System.Xml.Linq.dll. You will also need a using directive at the top of your code file:

using System.Xml.Linq;

(these are exactly the same two suggestions that the compiler itself makes: "are you missing a using directive or an assembly reference?")

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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.

C# – Populate XDocument from String

You can use XDocument.Parse for this.

Best Answer

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

C# – Populate XDocument from String

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