title: Android Alert Dialog on startup
body: <p>How can I achieve to show a Dialog automatically when an activity starts.
  If the activity is started a Dialog must be shown, where you must type a password.
  This password will be checked with the password stored in sharedpreferences, and if it is
  correct this activity will be shown,if not, a message will be shown on the dialog that the password is wrong and he must type it again.. I looked for some tutorials but all of them used a button to start the AlertDialog, but in my case It mus be shown when a specific activity is called. </p>
  
  <p>How can I achieve it?</p>