title: Update form from another form using delegate and event
body: <p>I keep forgetting how this is done..</p>
  
  <p>I want to update the UI on the main form from Form2 without creating an instance of the form.<br>
  I remember using a delegate / event and possibly passing in an instance of the first form somehow, but totally went blank. </p>
  
  <p>Help me out, thanks.</p>
  
  <p>Add something to listBox1 on Form1 from Form2.</p>