Trap closure of app when its closed in the Multi-Tasking view What event/selector/method is called, if any, when the user closes the app in the multi-tasking screen?  Xcode reports Message from debugger: Terminated due to signal 9 (i.e. SIGKILL, which cannot be trapped).
Is the use of AppDelegate.applicationWillResignActive,which is invoked when the user pressed the 'Home' button, the next best option?
It depends on the state your app is in:

If your app is suspended (i.e. it is in the background and not currently executing), there's no way of detecting the user closing the app.

If your app is backgrounded (i.e. it is in the background and executing), then your applicationWillTerminate method will be called.