Watch Extension Lifecycle
One useful addition brought by watchOS 2.0 is the WKExtensionDelegate protocol, which exposes lifecycle events and more. This protocol is similar to UIApplicationDelegate.
WKExtensionDelegate has three methods that let you respond to lifecycle events. The lifecycle methods will seem familiar:
There are also several methods you can implement to handle notifications.
And finally, you can implement
handleUserActivity() to facilitate Handoff.