iOS – How To Respond To The Application Launch In iOS ?

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In this article, We will learn how to respond to the application launch in iOS. We will discuss about initialize our app’s data structures, prepare our app to run, and respond to any launch-time requests from the system in iOS. We also describe why the app launched in iOS.

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So Let’s begin.

Overview

The system launches our app when the user taps our app’s icon on the Home screen. If our app requested specific events, the system might also launch our app in the background to handle those events. For a scene-based app, the system similarly launches the app when one of our scenes needs to appear onscreen or do some work.

All apps have an associated process, which the UIApplication object represents. Apps also have an app delegate object—an object that conforms to the UIApplicationDelegate protocol—which responds to important events happening within that process. Even a scene-based app uses an app delegate to manage fundamental events like launch and termination. At launch time, UIKit automatically creates the UIApplication object and our app delegate. It then starts our app’s main event loop.

Provide a Launch Storyboard

When the user first launches the app on a device, the system displays the launch storyboard until the app is ready to display its UI. Displaying the launch storyboard assures the user that our app launched and is doing something. If our app initializes itself and readies its UI quickly, the user may see the launch storyboard only briefly.

Xcode projects automatically include a default launch storyboard for us to customize, and we can add more launch storyboards as necessary. To add new launch storyboards to our project, do the following:

1. Open your project in Xcode.
2. Choose File > New > File.
3. Add a Launch Screen resource to our project.

Add views to our launch storyboard and use Auto Layout constraints to size and position them so that they adapt to the underlying environment. UIKit displays exactly what we provide, using our constraints to fit our views into the available space. We can use  Human Interface Guidelines for for design guidance.

In iOS 13 and later, always provide a launch storyboard for your app. Don’t use static launch images.

Initialize App’s Data Structures

We put our app’s launch-time initialization code in one or both of the following methods:

• application(_:willFinishLaunchingWithOptions:)
• application(_:didFinishLaunchingWithOptions:)

UIKit calls these methods at the beginning of our app’s launch cycle. We use them to:

• Initialize our app’s data structures.
• Verify that our app has the resources it needs to run.
• Perform any one-time setup when our app launches for the first time. For example, install templates or user-modifiable files in a writable directory.
• Connect to any critical services that our app uses. For example, connect to the Apple Push Notification service if our app supports remote notifications.
• Check the launch options dictionary for information about why our app launched.

For apps that aren’t scene-based, UIKit loads our default user interface automatically at launch time. Use the application(_:didFinishLaunchingWithOptions:) method to make additional changes to that interface before it appears onscreen. For example, we might install a different view controller to reflect what the user was doing the last time they used the app.

Move Long-Running Tasks off the Main Thread

When the user launches the app, make a good impression by launching quickly. UIKit doesn’t present the app’s interface until after the application(_:didFinishLaunchingWithOptions:) method returns. Performing long-running tasks in that method or the application(_:willFinishLaunchingWithOptions:) method might make the app appear sluggish to the user. Returning quickly is also important when launching to the background because the system limits the app’s background execution time.

Move tasks that are not critical to the app’s initialization out of the launch-time sequence. For example:

• Defer the initialization of features that the app doesn’t need immediately.
• Move important, long-running tasks off the app’s main thread. For example, run them asynchronously on a global dispatch queue.

Determine Why App Launched

When UIKit launches the app, it passes along a launch options dictionary to the application(_:willFinishLaunchingWithOptions:) and application(_:didFinishLaunchingWithOptions:) methods with information about why the app launched. The keys in that dictionary indicate important tasks to perform immediately. For example, they might reflect actions that the user started elsewhere and wants to continue in the app. Always check the contents of the launch options dictionary for keys that we expect, and respond appropriately to their presence.

For a scene-based app, examine the options that UIKit passes to the application(_:configurationForConnecting:options:) method to determine why it created the scene.

The example shows the app delegate method for an app that handles background location updates. When the location key is present, the app starts location updates immediately instead of deferring them until later. Starting location updates allows the Core Location framework to deliver the new location event.

class AppDelegate: UIResponder, UIApplicationDelegate, 
               CLLocationManagerDelegate {
    
   let locationManager = CLLocationManager()
   func application(_ application: UIApplication,
              didFinishLaunchingWithOptions launchOptions:
              [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
       
      // If launched because of new location data,
      //  start the visits service right away.
      if let keys = launchOptions?.keys {
         if keys.contains(.location) {
            locationManager.delegate = self
            locationManager.startMonitoringVisits()
         }
      }
       
      return true
   }
   // other methods…
}

The system doesn’t include a key unless our app supports the corresponding feature. For example, the system doesn’t include the remoteNotification key for an app that doesn’t support remote notifications.

That’s all about in this article.

Conclusion

In this article, We understood how to respond to the application launch in iOS. This article described about initialize our app’s data structures, prepare our app to run, and respond to any launch-time requests from the system in iOS.

Thanks for reading ! I hope you enjoyed and learned about the Application Launch Concepts in iOS. Reading is one thing, but the only way to master it is to do it yourself.

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• iOS Articles
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• AppCoda.com
• Raywenderlich.com

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