Hi Haggy,

You can create a FieldLayout from that string in code-behind but there's no way to use that string directly with the XamDataGrid to tell it to use that layout.  You can use the XamlReader class to convert that string into an actual FieldLayout object and then add it to the grid.  An example on how to use XamlReader can be seen here. 

StringReader sr = new StringReader(@"<igDP:FieldLayout xmlns:igDP='http://infragistics.com/DataPresenter'>
<igDP:Field Name='MyField' Label='Name'/>
</igDP:FieldLayout>");

XmlReader reader = XmlReader.Create(sr);
FieldLayout dynamicFieldLayout = (FieldLayout)XamlReader.Load(reader);

Let me know if you have any questions on this.