title: Save file with appropriate extension in a Save File prompt
body: <p>In my application I use a SaveFileDialog to pop up a Save As window. I have restricted in the file type section the file to be saved as .dat with the following code.</p>
  
  <pre><code>sfdialog.Filter = "Data Files (*.dat*)|*.dat*";
  </code></pre>
  
  <p>What I want to know how to do is make it automatically save with the .dat extension. Currently it just saves with no extension unless I specifically save it as filename.dat.</p>