title: Ionic / Angular Leave Page Event
body: <p>I have an Ionic v4 page that configures a number of parameters for my application and I want to stuff all those values into an injected service right before I navigate off of the page so they can be used elsewhere in the application. I am using the Ionic Tabs Control / Page for navigation.</p>
  
  <p>What is the best way to trap an event right before navigating off of the current page?</p>
  
  <p>I have played with <code>@angular/router</code> <code>NavigationStart</code> events but once wired up it fires on all page transitions and I can't tell when I am leaving the desired config page. Or should I be using the old Ionic v3 NavControl?</p>
  
  <p>Or should I just be updating my config service on all changes and not worry about leaving the page?</p>