title: How to add event listeners in Flutter?
body: <p>I'm pretty new to Flutter and experimenting with the SDK. I'm working on a simple app that has a countdown in the background and want to trigger an event at certain intervals. For example, when clock reaches one minute remaining, send a push notification. In general, I'm trying to get a feel for how to monitor certain activities such as time and usage of the app and once certain conditions are met, trigger other things. Is it as simple as an if-else statement placed in the right place?</p>
  
  <p>What kind of thing am I looking for to implement this?</p>
  
  <p>Thanks in advance.</p>