UISceneDelegate adoption

Apple now requires iOS developers to adopt the UISceneDelegate protocol, which changes the order of initialization when an application launches. If your app on iOS modifies application:didFinishLaunchingWithOptions:, it might have to be updated.

Most Flutter apps won't have custom logic inside of application:didFinishLaunchingWithOptions:. Those apps won't need to do any code migration. In most cases, Flutter automatically migrates the Info.plist.

Apple now requires the adoption of UISceneDelegate, which reorders the initialization of iOS apps. After a UISceneDelegate is specified, initialization of the Storyboard is delayed until after calling application:didFinishLaunchingWithOptions:. That means UIApplicationDelegate.window and UIApplicationDelegate.window.rootViewController can't be accessed from application:didFinishLaunchingWithOptions:.

Apple is driving the adoption of the UISceneDelegate API since it allows apps to have multiple instances of their UIs, like multitasking on iPadOS.

Previously, Flutter’s documentation indicated that application:didFinishLaunchingWithOptions: was a good place to set up platform channels to create interop between the host application and Flutter. That is no longer a reliable place to register these platform channels, since the Flutter engine won't have been created yet.

UISceneDelegates must be specified in an app's Info.plist or in application:configurationForConnectingSceneSession:options:. The Flutter tool attempts to automatically edit the Info.plist if no UISceneDelegate is specified, so nothing might be required beyond running flutter run or flutter build again. Projects can be manually upgraded by adding the following to the Info.plist. FlutterSceneDelegate is the new class in the Flutter framework that performs as the UISceneDelegate.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
 <key>UIApplicationSceneManifest</key>
 <dict>
  <key>UIApplicationSupportsMultipleScenes</key>
  <false/>
  <key>UISceneConfigurations</key>
  <dict>
  <key>UIWindowSceneSessionRoleApplication</key>
    <array>
      <dict>
        <key>UISceneClassName</key>
        <string>UIWindowScene</string>
        <key>UISceneDelegateClassName</key>
        <string>FlutterSceneDelegate</string>
        <key>UISceneConfigurationName</key>
        <string>flutter</string>
        <key>UISceneStoryboardFile</key>
        <string>Main</string>
      </dict>
    </array>
   </dict>
 </dict>
</dict>

As seen in Xcode's editor:

Apps that create the FlutterViewController programmatically can continue to operate as before. Apps that rely on Storyboards (and XIBs) to create platform channels in application:didFinishLaunchingWithOptions: should now use the FlutterPluginRegistrant API to accomplish the same thing.

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
      _ application: UIApplication,
      didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
    let batteryChannel = FlutterMethodChannel(name: "samples.flutter.dev/battery",
                                              binaryMessenger: controller.binaryMessenger)
    batteryChannel.setMethodCallHandler({
      [weak self] (call: FlutterMethodCall, result: FlutterResult) -> Void in
      // This method is invoked on the UI thread.
      // Handle battery messages.
    })

    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

@implementation AppDelegate
- (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
  FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;

  FlutterMethodChannel* batteryChannel = [FlutterMethodChannel
                                          methodChannelWithName:@"samples.flutter.dev/battery"
                                          binaryMessenger:controller.binaryMessenger];

  [batteryChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    // This method is invoked on the UI thread.
    // TODO
  }];

  [GeneratedPluginRegistrant registerWithRegistry:self];
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}
@end

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate, FlutterPluginRegistrant {
  override func application(
      _ application: UIApplication,
      didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    pluginRegistrant = self
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }

  func register(with registry: any FlutterPluginRegistry) {
    let registrar = registry.registrar(forPlugin: "battery")
    let batteryChannel = FlutterMethodChannel(name: "samples.flutter.dev/battery",
                                              binaryMessenger: registrar.messenger)
    batteryChannel.setMethodCallHandler({
      [weak self] (call: FlutterMethodCall, result: FlutterResult) -> Void in
      // This method is invoked on the UI thread.
      // Handle battery messages.
    })

    GeneratedPluginRegistrant.register(with: registry)
  }
}

@interface AppDelegate () <flutterpluginregistrant>
@end

@implementation AppDelegate
- (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
  self.pluginRegistrant = self;
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

- (void)registerWithRegistry:(NSObject<flutterpluginregistry>*)registry {
  NSObject<flutterpluginregistrar>* registrar = [registry registrarForPlugin:@"battery"];
  FlutterMethodChannel* batteryChannel = [FlutterMethodChannel
                                          methodChannelWithName:@"samples.flutter.dev/battery"
                                          binaryMessenger:registrar.messenger];

  [batteryChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    // This method is invoked on the UI thread.
    // TODO
  }];

  [GeneratedPluginRegistrant registerWithRegistry:registry];
}
@end

Set up the FlutterPluginRegistrant programmatically through the FlutterAppDelegate.

For apps that use a FlutterViewController instantiated from Storyboards in application:didFinishLaunchingWithOptions: for reasons other than creating platform channels, it is their responsibility to accommodate the new initialization order.

Migration options:

• Subclass FlutterViewController and put the logic in the subclasses' awakeFromNib.
• Specify a UISceneDelegate in the Info.plist or in the UIApplicationDelegate and put the logic in scene:willConnectToSession:options:. For more information, check out Apple's documentation.

@objc class MyViewController: FlutterViewController {
  override func awakeFromNib() {
    self.awakeFromNib()
    doSomethingWithFlutterViewController(self)
  }
}

• Landed in main: TBD
• Landed in stable: TBD
• Unknown: Apple changes their warning to an assert and Flutter apps that haven't adopted UISceneDelegate will start crashing on startup with the latest SDK.

• Issue 167267 - The initial reported issue.
• Apple's documentation on specifying UISceneDelegates