how can i pass xml string

I think one of the neat approaches would be to use class properties which you can set and make readonly if you want once set then no other class modifies the value.

Below is Class1 and Class2:

//Set property MyXml for Class2 like so:
public class Class1
{
    //e.g. I do it in the constructor here:
    public Class1( String myXml )
    {
        Class2 class2 = new Class2();
        class2.MyXml = myXml;
        //we are done here!
    }
}

public class Class2
{
   //class1 properties
   public String MyXml
   {
       get;set;
   }
   
   //access this property with the "this.MyXml" anywhere inside this class (Class2)
}

More on properties? there goes it:
http://msdn.microsoft.com/en-us/library/x9fsa0sw%28v=vs.80%29.aspx[^]

Happy coding,
Morgs