title: how to refer to main xaml from another class
body: <p>I want to update textblock1 to 'there' from a class other than the main.  As shown this code gives no errors, but does not work.  Textblock1 is set to
  FieldModifier="Public".</p>
  
  <pre><code>namespace myProgram
  {
      public sealed partial class MainPage : Page
      {
          Library stuff = new Library();
          public MainPage()
          {
              this.InitializeComponent();
          }
          public void mainStuff()
          {
              stuff.Doit(new MainPage());
          }
      }
  }
  namespace myProgram
  {
      public class Library
      {
          public void Doit(MainPage mainPage)
          {
              mainPage.textblock1.Text = "there";
          }
  
      }
  }
  </code></pre>