store the class into XML file

You can store (persist, store/load) not just a class, but an arbitrary object graph of any structure (not necessarily hierarchical) using Data Contract. This is most non-intrusive and easy-to-use approach; you only add attributes to types and members, so not modifications of types themselves are required.

See: http://msdn.microsoft.com/en-us/library/ms733127.aspx[^].

See also my past answers where I advocate this approach:
How can I utilize XML File streamwriter and reader in my form application?[^],
Creating property files...[^],
deseralize a json string array[^].

—SA