XDocument in Settings

I am trying 开发者_如何学Pythonto hand enter an XDocument in the settings pane of VS2010 without success. The type is System.Xml.Linq.XDocument

The message I get is:

Cannot be converted to an instance of type 'System.Xml.Linq.XDocument'

Does anyone know a way around this?

ST

You can't create an XDocument setting directly, because the XDocument class doesn't meet the criteria used by the Settings to determine if a type can be used:

Application settings can be stored as any data type that is XML serializable or has a TypeConverter that implements ToString/FromString. The most common types are String, Integer, and Boolean, but you can also store values as Color, Object, or as a connection string.

XDocument provides a way to create an XML document by parsing a string, but it's not a constructor, it's the static Load method (which takes a TextWriter, not a string). So it's not suited for use in the Settings.

But you can subclass it, and give the subclass a type converter. Fortunately, it's pretty easy to subclass XDocument with a type converter. First, create a subclass:

[TypeConverter(typeof(MyXDocumentTypeConverter))]
public class MyXDocument : XDocument
{
}

That class uses this TypeConverter:

public class MyXDocumentTypeConverter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return (sourceType == typeof (string));
    }

    public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
    {
        if (value is string)
        {
            MyXDocument d = new MyXDocument();
            d.Add(XDocument.Load(new StringReader((string) value)).Elements().First());
            return d;
        }
        return null;
    }
}

Once you have this set up, you can write code like this:

MyXDocument d = "<foo/>";

and the string <foo/> will get passed into the type converter and parsed (via Load) into an XDocument, whose top-level element then gets added to the MyXDocument. This is the same assignment that the auto-generated code in Settings.Designer.cs uses:

return ((global::XmlSettingsDemo.MyXDocument)(this["Setting"]));

Now you can go into your Settings dialog and create a setting of this type. You can't navigate to the type in the Type dialog; you have to manually enter the full name of the type (XmlSettingsDemo.MyXDocument was the name of mine).