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App Link is, technically, not a link, but metadata (eg. og:title and og:url) on a webpage.

It is called an App Link, because the webpage (with a URL link) usually open/install the app.

It is pretty interesting to learn about App Link for iOS, and specifically, I wil be introducing branch.io, which is a free deep linking service for both iOS and Android. And they claimed to be FREE forever!

Who else provides App Links?

Facebook and Google has their own service to create app links.

But they both required the user to login to Facebook/Google, which is a big disadvantage.

On the other hand, branch.io is neutral, and is very focused in doing what they do best.

Social Media Description

If you have an app, but doesn’t have a website, branch.io will be a great help for you to generate a link which you can share on social media platforms.

Behind the scene, the link generates the open graph metadata which describes your app.

App Link passes data over to app

This feature is the biggest reason why you should use branch.io.

We all know that when a user install an app from the App Store, no data can be passed to the app. eg. You won’t know the source/url that resulted in the user downloadong the app.

branch.io solved this problem by using fingerprinting. In short, it identifies a user with IDFA, then match it back after the app is installed. This is not perfect, but works 99%.

Setting up branch.io

The SDK integration guide is good.

The part on Universal and App Links is required too. They also provided good explanation on what’s changed in iOS 9.2. In short, Apple does not seamlessly open the app starting with iOS 9.2. Rather, it shows an alert and require the user to explicitly confirm first.

The code needed in AppDelegate:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    Branch.getInstance().initSessionWithLaunchOptions(launchOptions, andRegisterDeepLinkHandler: handleBranch)
}

func application(application: UIApplication, openURL url: NSURL, sourceApplication: String?, annotation: AnyObject) -> Bool {
    Branch.getInstance().handleDeepLink(url)
}
 
func application(application: UIApplication, continueUserActivity userActivity: NSUserActivity, restorationHandler: ([AnyObject]?) -> Void) -> Bool {
    return Branch.getInstance().continueUserActivity(userActivity)
}

// This branch handler will run when:
// - App Start
// - After `application:openURL:...`
// - After `application:continueUserActivity:...`
//
// Note the params will be "consumed". After the first run, on the subsequent, it will have `clicked_branch_link` false, `is_first_session` false
func handleBranch(params: [NSObject: AnyObject]!, error: NSError!) {
    if let error = error {
        print("Error: \(error)")
    }
    print("Branch Params: \(params)")
    // Handle it
}

Note: I am not very sure about this guide, which says to prevent “deep linked twice”. It has a flag, which is set to ignore in the entry point for iOS 8.x application:openURL:....

Handling Push

Branch can also handle the push notification payload, with the branch link url in key branch.

func application(application: UIApplication, didReceiveRemoteNotification launchOptions: [NSObject: AnyObject]?) -> Void {
    Branch.getInstance().handlePushNotification(launchOptions)
}