How to convert Objective-C App Delegate to Swift? - ios

Question

I am working on old projects converting all classes to Swift.
How can I convert the AppDelegate class to Swift?
What changes must me made in the Project settings or main.m?

Answer 1

A good starting point is to create a new Swift-Project to get the Template for the AppDelegate, or just copy the following code in your AppDelegate.swift class:
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
return true
}
func applicationWillResignActive(_ application: UIApplication) {
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
func applicationDidEnterBackground(_ application: UIApplication) {
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}
func applicationWillEnterForeground(_ application: UIApplication) {
// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}
func applicationDidBecomeActive(_ application: UIApplication) {
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}
func applicationWillTerminate(_ application: UIApplication) {
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground.
}
}
In Swift the main.m and AppDelegate class have been merged by using the #UIApplicationMain annotation. Therefore main.m is not required any longer and should be deleted from your project.
It's also not required to change your Project setting, hence the #UIApplicationMain will do the work for you. Just be sure to set the correct Target Membership of your AppDelegate class if you have more build targets with different AppDelegates.

Answer 2

Create a new file in Xcode (File > New > File…) and select a Cocoa Touch Class. Call it AppDelegate, make it a subclass of UIResponder and change the language to Swift.
Fill the AppDelegate.swift file with:
import UIKit
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool {
// Override point for customization after application launch.
return true
}
}
Remove your main.m and main.h files.
It's done!
Source: http://www.binpress.com/tutorial/converting-an-objective-c-app-to-swift/118

Answer 3

In order to improve #seeya answer
SWIFT 3
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
// Override point for customization after application launch.
return true
}
func applicationWillResignActive(_ application: UIApplication) {
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
func applicationDidEnterBackground(_ application: UIApplication) {
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}
func applicationWillEnterForeground(_ application: UIApplication) {
// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}
func applicationDidBecomeActive(_ application: UIApplication) {
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}
func applicationWillTerminate(_ application: UIApplication) {
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}
}

Answer 4

None of previous answers worked for me, after some researches, this worked:
import Foundation
import UIKit
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
var bridge: RCTBridge!
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
let jsCodeLocation: URL
jsCodeLocation = RCTBundleURLProvider.sharedSettings().jsBundleURL(forBundleRoot: "index.ios", fallbackResource:nil)
let rootView = RCTRootView(bundleURL: jsCodeLocation, moduleName: "REPLACE_BY_YOUR_PROJECT_NAME", initialProperties: nil, launchOptions: launchOptions)
let rootViewController = UIViewController()
rootViewController.view = rootView
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window?.rootViewController = rootViewController
self.window?.makeKeyAndVisible()
return true
}
}

Answer 5

Pasting solutions from the above answers, causes Xcode to suggest updating the function declaration to mark it a private. In this case the function will not be called by the system, and your app will never launch.
Swift 5
Use AppDelegate.swift as follows:
import UIKit
#main
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
let rootViewController = UIViewController() // replace with your view controller
window = UIWindow(frame: UIScreen.main.bounds)
window?.rootViewController = rootViewController
window?.makeKeyAndVisible()
return true
}
}