I recently built an Apple iOS WatchKit app and part of that was improving the user experience by leveraging Apple’s Handoff technology.

As seems to be the pattern lately with Apple’s WatchKit documentation, this turned out to take a few hours longer than it should have.

If you are trying to enable Apple’s Handoff and it isn’t working, it’s most likely because one of the three steps below wasn’t completed.

Three simple steps to handoff

In the end, it’s actually quite simple and Handoff comes down to a few small changes

  • Declaring what activities your iOS app can have “Handed off
  • Handing off from your WatchKit app to your iOS app
  • Receiving and processing the Handed off in your iOS app

Although this example is from WatchKit to iOS, you could do this from iOS to OSX.

Declaring activities

Ultimately, not just “anything” can be handed off to your iOS app. In order to get the hand off icon to appear on the iOS app, your iOS app must declare which activities it can handle.

To declare activities, you add the NSUserActivityTypes key to your apps plist file as an array, and then give meaningful names to the activities your app can handle.

NSUserActivityTypes Screenshot

Keep in mind, these are just symbolic names that you will reference from the WatchKit app and nothing more. So name them whatever makes the most sense to your app and these activities.

Handing off to your iOS app

In our WatchKit example below, when a customer slides up the WatchKit app’s Glance, we are going to initiate a hand off to iOS

override func awakeWithContext(context: AnyObject?) {
super.awakeWithContext(context)

let userInfo : [NSObject:AnyObject] = ["handoff_activity":"login"]

updateUserActivity("com.YourApp.YourDomain.loginHandoffAcivity",
userInfo: userInfo,
webpageURL: nil
)
}

At this point, Handoff still won’t work, as we haven’t “caught” the activity handed to our iOS app. However, this completes therequest to Handoff from the WatchKit app.

Preparing your app for iOS Handoff

First you need to update your iOS app AppDelegate. Specifically, you will need to add the continueUserActivity method.

func application(application: UIApplication, continueUserActivity userActivity: NSUserActivity, restorationHandler: ([AnyObject]!) -> Void) -> Bool {
restorationHandler([self.window!.rootViewController!])
return true
}

There are a few things in the above code snippet to notice, specifically the call to restorationHandler. The restorationHandler closure is the final step to make the Handoff icon appear on the iPhone’s lock screen.

Bringing it all together

These have been trivial examples, so ultimately you’re most likely going to do something like the following

override func awakeWithContext(context: AnyObject?) {
super.awakeWithContext(context)

let request : [NSObject:AnyObject] = ["request":"user_logged_in"]

//Send a request to your iOS app, most likely to fetch some remote data
WKInterfaceController.openParentApplication(request, reply: { (reply, error) -> Void in
//This is a hackish simplified short hand, you'll need to verify the response in the reply hash and parse out if the user has logged in
let user_logged_in = reply["response"]

if(user_logged_in == false){
//you can populate this hash with any relevant handoff or user data
let userInfo : [NSObject:AnyObject] = ["handoff_activity":"login"]

updateUserActivity("com.YourApp.YourDomain.loginHandoffAcivity",
userInfo: userInfo,
webpageURL: nil
)

//inform the user on your Glance UI that they need to log
some_func_to_display_the_login_ui_vs_the_normal_ui()
}
})
}