title: System.InvalidOperationException setting texbox text
body: <p>I am using one thread running this code:</p>
  
  <pre><code>try
  {
      Form1 f = getForm&lt;Form1&gt;();
      f.changePrice(price);
  }
  catch (Exception e)
  {
      Console.WriteLine("error: " + e);
  }
  </code></pre>
  
  <p>Here is the <code>changePrice</code> method:</p>
  
  <pre><code>public void changePrice(Int32 price)
  {
     txtPrice.Text = ""+price;
  }
  </code></pre>
  
  <p>I want to add text to my textbox "txtPrice".</p>