title: appendtext on text box only shown in the end all together in wpf
body: <p>I have a simple textbox in my program. 
  Other features : another input from the user textbox1, and a button. 
  Once the user enters a value in textbox1, and presses the button, I start to check and print messages to the user. My problem is that I don't see those messages on real time, one at a time. The messages appear at once, in the end. 
  I didn't define data binding, because I thought that since it's a simple thing, I wouldn't need it, or am i wrong ? 
  This is a very small portion of my program, it's in the button click event handler. </p>
  
  <pre><code>MainText.AppendText("Starting Refiling...\u2028");
  foreach (DocumentData doc in Docs)
  {
      try
      {
          wsProxy.RefileDocument(doc);
          MainText.AppendText(String.Format("Refilling doc # {0}.{1}\u2028", doc.DocNum, doc.DocVer));
      }
      catch (Exception exc)
      {
          if (exc.Message.Contains("Document is in use") == true)
              MainText.AppendText(String.Format("There was a problem refilling doc # {0}, it is in use.\u2028",doc.DocNum));
          else
              MainText.AppendText(String.Format("There was a problem refilling doc # {0} : {1}.\u2028", doc.DocNum, exc.Message));
      }
  }
  </code></pre>