Add a note on working around a potential crash on iOS (#13244)

Fixes #13243

---------

Co-authored-by: John Ryan <ryjohn@google.com>

Author: sfshaza2

src/content/platform-integration/ios/platform-views.md

@@ -169,21 +169,18 @@ modify the App's `AppDelegate.swift`:
 import Flutter
 import UIKit
 
-@UIApplicationMain
-@objc class AppDelegate: FlutterAppDelegate {
-    override func application(
-        _ application: UIApplication,
-        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]?
-    ) -> Bool {
-        GeneratedPluginRegistrant.register(with: self)
+@main
+@objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
+   
+    func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
+        GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
 
-        guard let pluginRegistrar = self.registrar(forPlugin: "plugin-name") else { return false }
+        guard let pluginRegistrar = engineBridge.pluginRegistry.registrar(forPlugin: "plugin-name") else { return }
 
         let factory = FLNativeViewFactory(messenger: pluginRegistrar.messenger())
         pluginRegistrar.register(
             factory,
             withId: "<platform-view-type>")
-        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
     }
 }
 ```
@@ -298,19 +295,16 @@ modify the App's `AppDelegate.m`:
 
 @implementation AppDelegate
 
-- (BOOL)application:(UIApplication *)application
-    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
-  [GeneratedPluginRegistrant registerWithRegistry:self];
+- (void)didInitializeImplicitFlutterEngine:(NSObject<FlutterImplicitEngineBridge>*)engineBridge {
+  [GeneratedPluginRegistrant registerWithRegistry:engineBridge.pluginRegistry];
 
-   NSObject<FlutterPluginRegistrar>* registrar =
-      [self registrarForPlugin:@"plugin-name"];
+  NSObject<FlutterPluginRegistrar>* registrar =
+      [engineBridge.pluginRegistry registrarForPlugin:@"plugin-name"];
 
   FLNativeViewFactory* factory =
       [[FLNativeViewFactory alloc] initWithMessenger:registrar.messenger];
 
-  [[self registrarForPlugin:@"<plugin-name>"] registerViewFactory:factory
-                                                          withId:@"<platform-view-type>"];
-  return [super application:application didFinishLaunchingWithOptions:launchOptions];
+  [registrar registerViewFactory:factory withId:@"<platform-view-type>"];
 }
 
 @end

src/content/platform-integration/platform-channels.md

@@ -612,24 +612,30 @@ Override the `application:didFinishLaunchingWithOptions:` function and create
 a `FlutterMethodChannel` tied to the channel name
 `samples.flutter.dev/battery`:
 
+:::note
+If your app adopts the `UISceneDelegate` lifecycle (default in Flutter 3.41+),
+`window` will be `nil` during `application(_:didFinishLaunchingWithOptions:)`.
+To avoid a crash, use the `FlutterImplicitEngineDelegate` protocol and
+create your `FlutterMethodChannel` in the `didInitializeImplicitFlutterEngine` method.
+:::
+
 ```swift title="AppDelegate.swift"
 @main
-@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)
+@objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
+   
+  func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
+    GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
+
+    let batteryChannel = FlutterMethodChannel(
+      name: "samples.flutter.dev/battery",
+      binaryMessenger: engineBridge.applicationRegistrar.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: self)
-    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
   }
 }
 ```
@@ -695,26 +701,32 @@ didFinishLaunchingWithOptions:` method.
 Make sure to use the same channel name
 as was used on the Flutter client side.
 
+:::note
+If your app adopts the `UISceneDelegate` lifecycle (default in Flutter 3.41+),
+`window` will be `nil` during `application:didFinishLaunchingWithOptions:`.
+To avoid a crash, use the `FlutterImplicitEngineDelegate` protocol and
+create your `FlutterMethodChannel` in the `didInitializeImplicitFlutterEngine` method.
+:::
+
 ```objc title="AppDelegate.m"
 #import <Flutter/Flutter.h>
 #import "GeneratedPluginRegistrant.h"
 
 @implementation AppDelegate
-- (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
-  FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;
+
+- (void)didInitializeImplicitFlutterEngine:(NSObject<FlutterImplicitEngineBridge>*)engineBridge {
+  [GeneratedPluginRegistrant registerWithRegistry:engineBridge.pluginRegistry];
 
   FlutterMethodChannel* batteryChannel = [FlutterMethodChannel
-                                          methodChannelWithName:@"samples.flutter.dev/battery"
-                                          binaryMessenger:controller.binaryMessenger];
+                                        methodChannelWithName:@"samples.flutter.dev/battery"
+                                        binaryMessenger:engineBridge.applicationRegistrar.messenger];
 
   [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
 ```
 
 Next, add the iOS ObjectiveC code that uses the iOS battery APIs to