title: What kind of Intent is used for choosing between applications, and how to listen for it?
body: <p>I am trying to create a kind of file manager to allow the user to upload files (from the file manager) to the internet.</p>
  
  <p>I would like to understand how this application would be triggered.</p>
  
  <p>For example:
  When using Gmail and pressing the add-attachment button, Android shows me two applications (the Gallery and FileExpert) to pick the content from.</p>
  
  <ul>
  <li>How is this accomplished? </li>
  <li>What kind of Intent is brodacasted (if an intent is used)?  </li>
  <li>What kind of object are the Gallery and FileManager that are able to be invoked
  by pressing the add-attachment button?</li>
  </ul>