[iOS] FlutterViewController Memory Leak

[JackCostigan]

Steps to reproduce

I am adding flutter screens to an existing iOS app using the add-to-app process.
I am using a subclass of FlutterViewController, and have found that it doesn't get collected by ARC after the view controller is popped off the navigation stack, as expected.

This behaviour is also present in the multiple flutters add-to-app sample code here.

Steps to reproduce:

1. Build and run the "multiple flutters iOS" project as described at the link above.
2. Tap the "Next" button to push an instance of SingleFlutterViewController onto the navigation stack.
3. Press the back button to pop the SingleFlutterViewController off the navigation stack.
4. Use the "Debug Memory Graph" feature on Xcode, and search for SingleFlutterViewController.

Expected result:
The SingleFlutterViewController has been collected by ARC and is not present in the memory graph.

Actual result:
The SingleFlutterViewController is present in the memory graph, even after it has been removed from the navigation controller.

Also note that pushing and popping multiple instances of SingleFlutterViewController will result in multiple instances being kept in the memory graph.

See attached screenshot of the Xcode memory graph.

Experimentally, I found that calling destroyContext() on the FlutterViewControllers engine instance will cause the FlutterViewController to be collected.

So reworking the sample code as below fixes the issue, however I don't think I should have to manually call destroyContext.

class SingleFlutterViewController: UIViewController, DataModelObserver {
  private var channel: FlutterMethodChannel?
  private let flutterViewController: FlutterViewController

  init(withEntrypoint entryPoint: String?) {
    let appDelegate: AppDelegate = UIApplication.shared.delegate as! AppDelegate
    let newEngine = appDelegate.engines.makeEngine(withEntrypoint: entryPoint, libraryURI: nil)
    GeneratedPluginRegistrant.register(with: newEngine)
    flutterViewController = FlutterViewController(engine: newEngine, nibName: nil, bundle: nil)
    super.init(nibName: nil, bundle: nil)
    DataModel.shared.addObserver(observer: self)
  }

  deinit {
    DataModel.shared.removeObserver(observer: self)
    flutterViewController.engine.destroyContext()
  }

  required init(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  func onCountUpdate(newCount: Int64) {
    if let channel = channel {
      channel.invokeMethod("setCount", arguments: newCount)
    }
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    view.addSubview(flutterViewController.view)
    flutterViewController.view.frame = view.bounds
    addChild(flutterViewController)
    flutterViewController.didMove(toParent: self)
    channel = FlutterMethodChannel(
        name: "multiple-flutters", binaryMessenger: flutterViewController.engine.binaryMessenger)
    channel!.invokeMethod("setCount", arguments: DataModel.shared.count)
    let navController = self.navigationController!
    channel!.setMethodCallHandler { (call: FlutterMethodCall, result: @escaping FlutterResult) in
      if call.method == "incrementCount" {
        DataModel.shared.count = DataModel.shared.count + 1
        result(nil)
      } else if call.method == "next" {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: "NativeViewCount")
        navController.pushViewController(vc, animated: true)
        result(nil)
      } else {
        result(FlutterMethodNotImplemented)
      }
    }
  }
}

Code sample

Code sample

As described above, see the add to app multiple flutters example.

What target platforms are you seeing this bug on?

iOS

OS/Browser name and version | Device information

I'm building using Xcode 16.2 and Mac OS 15.3.1.
I'm using Flutter 3.29.0.
I am running on an iPhone 16 Pro simulator, using iOS 18.3

Does the problem occur on emulator/simulator as well as on physical devices?

Unknown

Logs

Logs

[Paste your logs here]

Flutter Doctor output

Doctor output

[✓] Flutter (Channel stable, 3.29.0, on macOS 15.3.1 24D70 darwin-arm64 (Rosetta), locale en-GB) [895ms]
    • Flutter version 3.29.0 on channel stable at /Users/jackcostigan/development/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 35c388afb5 (11 days ago), 2025-02-10 12:48:41 -0800
    • Engine revision f73bfc4522
    • Dart version 3.7.0
    • DevTools version 2.42.2

[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0) [933ms]
    • Android SDK at /Users/jackcostigan/Library/Android/sdk
    ✗ cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    ✗ Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/to/macos-android-setup for more details.

[✓] Xcode - develop for iOS and macOS (Xcode 16.2) [1,694ms]
    • Xcode at /Applications/Xcode-16.2.0.app/Contents/Developer
    • Build 16C5032a
    • CocoaPods version 1.16.2

[✗] Chrome - develop for the web (Cannot find Chrome executable at /Applications/Google Chrome.app/Contents/MacOS/Google
    Chrome) [47ms]
    ! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.

[✓] Android Studio (version 2023.1) [46ms]
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.7+0-17.0.7b1000.6-10550314)

[✓] VS Code (version 1.90.0) [42ms]
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension can be installed from:
      🔨 https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[✓] Connected device (3 available) [7.4s]
    • iPhone 16 Pro (mobile)          • C292E601-ED3D-4EFD-BC77-517D624BD6C7 • ios          • com.apple.CoreSimulator.SimRuntime.iOS-18-3
      (simulator)
    • macOS (desktop)                 • macos                                • darwin-arm64 • macOS 15.3.1 24D70 darwin-arm64 (Rosetta)
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad                • darwin       • macOS 15.3.1 24D70 darwin-arm64 (Rosetta)

[✓] Network resources [913ms]
    • All expected network resources are available.

! Doctor found issues in 2 categories.

[EvanMasterson]

+1 seeing the exact same issue

[huycozy]

Hi @JackCostigan
This looks similar to #77621 that you please check and confirm?

[JackCostigan]

@huycozy Thats interesting. The issue could be related.

From my reading of the other issue, the high memory usage occurs in debug mode, and in release/profile mode the issue does not occur.

I re-tested my code using a profile build, and I do not see the memory leak anymore.

However, this behaviour is still very surprising to me. I understand that the dart vm runs JIT (rather than AOT) when run in debug mode, but FlutterViewController is an objc class. I would have assumed that its memory would be managed on the iOS side, using ARC.

Can you offer any insight into why the dart vm behaviour effects the reference counting of objc objects?

[huycozy]

Thanks for the update. Labeling this issue for further input from team.

Reproduced this on Flutter stable 3.29.0 using add_to_app/multiple_flutters sample code. On master channel, I encountered another issue as below:

error: [+1853 ms] ../../../../../../GitHub/flutter_master/packages/flutter/lib/src/widgets/table.dart:443:50: Error: Member not found: 'cell'.

Another observation: When I see lldb from the output console, I add bt to see if can get full trace log and it's here:

Output log

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
  * frame #0: 0x000000010ce3bf0e libsystem_kernel.dylib`mach_msg2_trap + 10
    frame #1: 0x000000010ce4a5fa libsystem_kernel.dylib`mach_msg2_internal + 84
    frame #2: 0x000000010ce43016 libsystem_kernel.dylib`mach_msg_overwrite + 649
    frame #3: 0x000000010ce3c1ff libsystem_kernel.dylib`mach_msg + 19
    frame #4: 0x00007ff80042f23f CoreFoundation`__CFRunLoopServiceMachPort + 143
    frame #5: 0x00007ff8004297c3 CoreFoundation`__CFRunLoopRun + 1393
    frame #6: 0x00007ff800428e11 CoreFoundation`CFRunLoopRunSpecific + 550
    frame #7: 0x00007ff811d2b0cb GraphicsServices`GSEventRunModal + 137
    frame #8: 0x00007ff8064a5840 UIKitCore`-[UIApplication _run] + 875
    frame #9: 0x00007ff8064aa781 UIKitCore`UIApplicationMain + 123
    frame #10: 0x00007ff805413c33 UIKitCore`UIKit.UIApplicationMain(Swift.Int32, Swift.Optional<Swift.UnsafeMutablePointer<Swift.UnsafeMutablePointer<Swift.Int8>>>, Swift.Optional<Swift.String>, Swift.Optional<Swift.String>) -> Swift.Int32 + 99
    frame #11: 0x000000010cb9492b MultipleFluttersIos.debug.dylib`static UIApplicationDelegate.main() at <compiler-generated>:0
    frame #12: 0x000000010cb948a7 MultipleFluttersIos.debug.dylib`static AppDelegate.$main() at <compiler-generated>:0
    frame #13: 0x000000010cb949d8 MultipleFluttersIos.debug.dylib`main at AppDelegate.swift:10:7
    frame #14: 0x000000010cc38478 dyld_sim`start_sim + 10
    frame #15: 0x0000000111c442cd dyld`start + 1805

flutter version

[✓] Flutter (Channel stable, 3.29.0, on macOS 15.3.1 24D70 darwin-x64, locale en-VN) [701ms]
    • Flutter version 3.29.0 on channel stable at /Users/huynq/Documents/GitHub/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 35c388afb5 (2 days ago), 2025-02-10 12:48:41 -0800
    • Engine revision f73bfc4522
    • Dart version 3.7.0
    • DevTools version 2.42.2