title: Automation add-in vs. COM add-in
body: <p>I am a newbie with add-in programming and need help with the following scenario:</p>
  
  <p>I have an C# Excel automation add-in that calls a few <code>UDF</code>s. I want to do a user name and password check during when the automation add-in loads for which a screen where the user can enter his details must pop up on load of the add-in. How can it be done using an automation add-in? </p>
  
  <p>How can event handling be done in general using automation addins ? I want some calculations to be done when the user presses <kbd>F9</kbd> to calculate the UDF formula in some of the cells.</p>
  
  <p><s>Are there any articles that explains event handling in automation add-ins?</s></p>