[iOS]: Plugin Registration crash when adopting UISceneDelegate due to nil FlutterEngine #168228
Description
When following Apple's best practices of adopting UISceneDelegate, if the project uses any swift plugins, the project will crash at launch when plugins are registered because the objc bridge classes for swift FlutterPlugin subclasses will be nil.
I ran into this crash while trying to implement #167267, but I've also seen users in the wild running into this crash as well ( https://developer.apple.com/forums/thread/748671 ).
reproduction steps
flutter create -t plugin --platform=ios swiftplugincd swiftplugin- Add the following to
example/ios/Runner/Info.plist(Note that the value of the fields don't need to be valid because startup will crash before it is used).<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>$(PRODUCT_MODULE_NAME).AppDelegate</string> <key>UISceneConfigurationName</key> <string>flutter</string> <key>UISceneStoryboardFile</key> <string>Main</string> </dict> </array> </dict> </dict>
cd example; flutter run
crash
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
frame #0: 0x0000000194f85b08 libswiftCore.dylib`swift_getObjectType + 36
frame #1: 0x000000010329935c plugintest`static PlugintestPlugin.register(registrar=__C.FlutterPluginRegistrar @ 0x000000016ce08b88) at PlugintestPlugin.swift:0
* frame #3: 0x000000010325d834 Runner.debug.dylib`+[GeneratedPluginRegistrant registerWithRegistry:](self=GeneratedPluginRegistrant, _cmd="registerWithRegistry:", registry=0x0000600000c0daa0) at GeneratedPluginRegistrant.m:25:3
frame #4: 0x000000010325d8c4 Runner.debug.dylib`AppDelegate.application(application=0x0000000103f05a80, launchOptions=nil) at AppDelegate.swift:10:31
frame #6: 0x0000000185b2e30c UIKitCore`-[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 312
frame #7: 0x0000000185b2f804 UIKitCore`-[UIApplication _callInitializationDelegatesWithActions:forCanvas:payload:fromOriginatingProcess:] + 2936
frame #8: 0x0000000185b34984 UIKitCore`-[UIApplication _runWithMainScene:transitionContext:completion:] + 976
frame #9: 0x00000001851405ec UIKitCore`-[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:] + 148
frame #10: 0x0000000185b316b0 UIKitCore`-[UIApplication _compellApplicationLaunchToCompleteUnconditionally] + 44
frame #11: 0x0000000185b319b8 UIKitCore`-[UIApplication _run] + 760
frame #12: 0x0000000185b35bd4 UIKitCore`UIApplicationMain + 124
frame #13: 0x0000000184f0a334 UIKitCore`UIKit.UIApplicationMain(Swift.Int32, Swift.Optional<Swift.UnsafeMutablePointer<Swift.UnsafeMutablePointer<Swift.Int8>>>, Swift.Optional<Swift.String>, Swift.Optional<Swift.String>) -> Swift.Int32 + 100
frame #16: 0x000000010325de10 Runner.debug.dylib`main at <compiler-generated>:0
frame #17: 0x0000000103009410 dyld_sim`start_sim + 20
frame #18: 0x00000001030d6b4c dyld`start + 6000
Inspecting the type in the debugger after the crash looks like this:
(lldb) po PlugintestPlugin.self
note: error: No module map file in /Users/aaclarke/Library/Developer/Xcode/DerivedData/Runner-akumchbkelcnzlcblbxzpccssdcp/Build/Products/Debug-iphonesimulator/Flutter.framework
error: Error [IRForTarget]: Couldn't resolve the class for an Objective-C static method call
doctor
[!] Flutter (Channel [user-branch], 3.32.0-1.0.pre.382, on macOS 15.4.1 24E263 darwin-arm64, locale en) [551ms]
! Flutter version 3.32.0-1.0.pre.382 on channel [user-branch] at /Users/aaclarke/dev/flutter
Currently on an unknown channel. Run `flutter channel` to switch to an official channel.
If that doesn't fix the issue, reinstall Flutter by following instructions at https://flutter.dev/setup.
! Upstream repository unknown source is not a standard remote.
Set environment variable "FLUTTER_GIT_URL" to unknown source to dismiss this error.
• Framework revision 448e3036e0 (28 minutes ago), 2025-05-02 09:38:10 -0700
• Engine revision 9ffc2d9ef3
• Dart version 3.9.0 (build 3.9.0-76.0.dev)
• DevTools version 2.46.0-dev.0
• If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and upgrades.
[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0-rc4) [1,093ms]
• Android SDK at /Users/aaclarke/Library/Android/sdk
• Emulator version 35.2.10.0 (build_id 12414864) (CL:N/A)
• Platform android-35, build-tools 35.0.0-rc4
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To change the current JDK, run: `flutter config --jdk-dir="path/to/jdk"`.
✗ Cannot execute path/to/jdk/bin/java to determine the version
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• Xcode at /Applications/Xcode.app/Contents/Developer
• Build 16E140
! CocoaPods 1.15.2 out of date (1.16.2 is recommended).
CocoaPods is a package manager for iOS or macOS platform code.
Without CocoaPods, plugins will not work on iOS or macOS.
For more info, see https://flutter.dev/to/platform-plugins
To update CocoaPods, see https://guides.cocoapods.org/using/getting-started.html#updating-cocoapods
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[✓] Connected device (4 available) [6.3s]
• iPhone (5) (wireless) (mobile) • 00008110-001524D40A10401E • ios • iOS 18.4.1 22E252
• iPhone 16 Pro (mobile) • 9DA578E6-E85A-44FA-9673-D01C31F3B779 • ios • com.apple.CoreSimulator.SimRuntime.iOS-18-2 (simulator)
• macOS (desktop) • macos • darwin-arm64 • macOS 15.4.1 24E263 darwin-arm64
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